Engine Cooling System GMC Yukon Denali GMT800

Fastener Tightening Specifications

Fastener Tightening Specifications

Scheme 30

Scheme 31

Scheme 32

Cooling System Connector End Views

Coolant Level Switch Connector End Connector Part Information 12052644 2-Way F Metri-Pack 150 Series Sealed (GRY) Pin Wire Color Circuit No. Function A LT GRN 1478 Coolant Level Switch Signal B BLK 550 Ground

Engine Coolant Temperature (ECT) Sensor Connector End Connector Part Information 12162194 2-Way F Metri-Pack 150.2 Series Sealed (BLK) Pin Wire Color Circuit No. Function A GRY 720 Low Reference B YEL 410 ECT Sensor Signal

Diagnostic Starting Point - Engine Cooling

Begin the system diagnosis with the DIAGNOSTIC SYSTEM CHECK - Engine Cooling . The Diagnostic System Check will provide the following information

1. The identification of the control module(s) which command the system.
2. The ability of the control module(s) to communicate through the serial data circuit.
3. The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 3: Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
2. 4: Determine if the Instrument Cluster or Powertrain Control Modules have set DTCs which may affect Engine Cooling operation are present.
3. 5: The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

Diagnostic System Check - Engine Cooling

Scan Tool Output Controls

Instrument Cluster Scan Tool Output Controls

Scan Tool Data List

Instrument Panel Cluster (IPC) Scan Tool Data List

Powertrain Control Module (PCM) 4.3L Scan Tool Data List

Powertrain Control Module (PCM) 4.8L, 5.3L, and 6.0L Scan Tool Data List

Powertrain Control Module (PCM) 8.1L Scan Tool Data List

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

The PCM uses the ECT sensor to monitor the engine for an over temperature condition. This condition occurs when the coolant temperature is above 132°C (270°F). When an over temperature condition is present, DTC P1258 will set. The PCM will disable two groups of four cylinders by turning OFF the fuel injectors. By switching between the two groups of cylinders, the PCM is able to reduce the temperature of the coolant.

Conditions for Running the DTC

1. DTCs P0117, P0118, P1114, and P1115 are not active.
2. The engine is running.

Conditions for Setting the DTC

The engine coolant temperature is above 132°C (270°F) for 10 seconds or more.

Action Taken When the DTC Sets

1. The PCM will illuminate the malfunction indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
2. The PCM will signal the IPC to turn ON the Service Engine Soon indicator.
3. The PCM will alternately disable two groups of four cylinders by turning OFF the fuel injectors.
4. The PCM will store conditions which were present when the DTC set as Freeze Frame and File Records data.

Conditions for Clearing the MIL/DTC

1. The PCM will turn the MIL OFF after 3 consecutive trips that the diagnostic has been run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using the scan tool Clear DTC Information function.

DTC P1258

Symptoms - Engine Cooling

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the Cooling System. Refer to «CHECKING AFTERMARKET ACCESSORIES»(/gmc/yukon-denali/gmt800-1999-2006/remont/accessories-control-systems/#wiring-systems-general-information__checking-aftermarket-accessories) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Inspect the surge tank reservoir for the proper coolant level.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Engine Overheated Indicator Always On»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__engine-overheated-indicator-always-on)
2. «Engine Coolant Temperature Indicator Always On»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__engine-coolant-temperature-indicator-always-on)
3. «Low Engine Coolant Indicator Always On»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__low-engine-coolant-indicator-always-on)
4. «Coolant Heater Inoperative»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__coolant-heater-inoperative)
5. «Engine Overheating»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__engine-overheating)
6. «Loss of Coolant»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__loss-of-coolant)
7. «Thermostat Diagnosis»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system)
8. «Engine Fails To Reach Normal Operating Temperature»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__engine-fails-to-reach-normal-operating)
9. «Fan Clutch Diagnosis»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-diagnosis)

Engine Overheated Indicator Always On

Engine Overheated Indicator Always On

Engine Coolant Temperature Indicator Always On

Engine Coolant Temperature Indicator Always On

Low Engine Coolant Indicator Always On

Low Engine Coolant Indicator Always On

Engine Overheating

Engine Overheating

Loss of Coolant

Loss of Coolant

Tools Required

J 24731 Tempil Stick

Use one of the following procedures in testing for a malfunctioning thermostat.

Thermostat Test Procedure Using Tempil Sticks

The coolant thermostat can be tested using a temperature (tempil) stick. The temperature stick is a pencil like device. It has a wax material containing certain chemicals which melt at a given temperature. Temperature sticks can be used to determine a thermostat's operating range, by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing.

1. Use a tempil stick in order to find the opening and the closing temperatures of the coolant thermostat. J 24731 -188 tempil stick melts at 87°C (188°F). The thermostat should begin to open. J 24731 -206 tempil stick melts at 97°C (206°F). The thermostat should be fully open.
2. Replace the coolant thermostat if it does not operate properly between this temperature range.

Thermostat Test Procedure Using Glycol

Inspect the operation of the thermostat by hanging the thermostat on a hook in a 50/50 percent solution of DEX-COOL® and clean drinkable water.

In order to inspect if the thermostat valve is opening properly, perform the following test

1. Completely submerge the thermostat in the glycol solution. The solution should be 11°C (22°F) above the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should open.

In order to inspect if the thermostat valve is closing properly, perform the following test

1. Completely submerge the thermostat in a glycol solution. The solution should be 6°C (10°F) below the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.

Coolant Heater Inoperative

Coolant Heater Inoperative

Engine Fails To Reach Normal Operating Temperature

Engine Fails To Reach Normal Operating Temperature

Pressure Cap Testing

Tools Required

J 24460-01 Cooling System Pressure Tester

1. Remove the pressure cap.
2. Wash the pressure cap sealing surface with water.
3. Use the J 24460-01 in order to test the pressure cap.
4. Test the pressure cap for the following conditions: Pressure release when the J 24460-01 exceeds the pressure rating of the pressure cap. Maintain the rated pressure for at least 10 seconds.
5. Replace the pressure cap under the following conditions: The pressure cap does not release pressure which exceeds the rated pressure of the cap. The pressure cap does not hold the rated pressure.

Cooling System Leak Testing

Tools Required

J 24460-01 Cooling System Pressure Tester

1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__pressure-cap-testing) .
3. Use the J 24460-01 in order to apply pressure to the cooling system. Do not exceed the pressure cap rating.
4. The cooling system should hold the rated pressure for at least 2 minutes. Observe the gage for any pressure loss.
5. Repair any leaks as required.

Fan Clutch Diagnosis

Fan Clutch Diagnosis

Drain and Fill Procedure

Note. The procedure below must be followed. Improper coolant level could result in a low or high coolant level condition, causing engine damage.

1. Park the vehicle on a level surface.
2. Follow the steps below in order to remove the surge tank fill cap: Slowly rotate the cap counterclockwise. Stop rotating and allow the hissing to stop. After all hissing stops, continue turning counterclockwise in order to remove the cap.
3. Open the radiator drain cock.
4. Allow the system to drain completely.
5. Inspect the engine coolant for the following: Discolored - follow the flush procedure below. Normal in appearance - continue with the next step. NOTE: When adding coolant, use DEX-COOL® coolant. If silicated coolant is added to the system, premature engine, heater core or radiator corrosion may result. In addition, the engine coolant will require change sooner-at 50 000 km (30,000 mi) or 24 months.
6. Close the radiator drain cock.
7. Fill the system through the surge tank opening.
8. Pre-mix a 50 to 60 percent solution of DEX-COOL® and clean, drinkable water.
9. Slowly add the pre-mixed solution to the surge tank until the level is slightly above the COLD FILL mark.
10. Start the engine.
11. Idle the engine for 1 minute.
12. Loosely install the surge tank cap. DO NOT allow the system to build up pressure.
13. Cycle the engine from idle to 3,000 RPM in 30 second intervals until the engine coolant reaches 99°C (210°F) and the thermostat opens.
14. Shut off the engine.
15. Refer to step 2 in order to remove the surge tank cap.
16. Start the engine.
17. Idle the engine for 1 minute. Fill the surge tank to 12.7 mm (1/2 in) above the COLD FILL mark on the surge tank.
18. Install the radiator surge tank cap.
19. Cycle the engine from idle to 3,000 RPM in 30 second intervals until the engine coolant reaches 99°C (210°F) and the thermostat opens.
20. Shut off the engine.
21. Top off the coolant, as necessary, to 12.7 mm (1/2 in) above the COLD FILL mark on the surge tank.
22. Rinse away any excess coolant from the engine and the engine compartment.
23. Inspect the concentration of the coolant.

Engine Block Draining

1. Drain the cooling system, refer to the above procedure.
2. If equipped with the 4.8L, 5.3L or 6.0L engine, remove the left and right engine block coolant drain plugs.
3. If equipped with the 8.1L engine, remove the left and right engine block coolant drain plugs.
4. Remove the engine block coolant heater, if equipped. Refer to «COOLANT HEATER REPLACEMENT (DEALER INSTALLATION - 6.0L Engine)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «Coolant Heater Replacement (4.8L, 5.3L, and 6.0L Engines)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «Coolant Heater Replacement (8.1L Engine)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Allow the engine block to drain completely.
6. Apply sealant GM P/N 12346004 (Canadian P/N 10953480) or equivalent to the drain plugs.
7. Reinstall the engine block coolant drain plugs. Tighten: Tighten the 4.8L, 5.3L or 6.0L engine block coolant drain plug to 60 N.m (44 lb ft). Tighten the 8.1L engine block coolant drain plug to 60 N.m (44 lb ft).
8. Install the engine block coolant heater, if equipped. Refer to «COOLANT HEATER REPLACEMENT (DEALER INSTALLATION - 6.0L Engine)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «Coolant Heater Replacement (4.8L, 5.3L, and 6.0L Engines)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «Coolant Heater Replacement (8.1L Engine)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
9. Fill the cooling system, refer to the above procedure.

Flushing

Radiator Cleaning

Note. The radiator fins are necessary for good heat transfer. Do not brush the fins. This may cause damage to the fins, reducing heat transfer.

1. Some conditions may require the use of warm water and a mild detergent.
2. Clean the A/C condenser fins.
3. Clean between the A/C condenser and radiator.
4. Clean the radiator cooling fins.
5. Straighten any damaged cooling fins.

Removal Procedure

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the air cleaner assembly.
3. Remove the surge tank overflow hose from the surge tank.
4. Disconnect the low coolant level switch electrical connector (3).
5. Reposition the surge tank inlet hose clamp.
6. Remove the surge tank inlet (1) hose from the surge tank.
7. Reposition the surge tank outlet hose clamp.
8. Remove the surge tank outlet hose (2) from the surge tank.
9. Remove the bolt from the surge tank.
10. Remove the nut from the surge tank.
11. Remove the surge tank.

Installation Procedure

1. Install the surge tank.
2. Install the bolt to the surge tank. Tighten: Tighten the bolt to 9 N.m (80 lb in).
3. Install the nut to the surge tank. Tighten: Tighten the nut to 9 N.m (80 lb in).
4. Install the surge tank outlet hose (2) to the surge tank.
5. Position the surge tank outlet hose clamp.
6. Install the surge tank inlet hose (1) to the surge tank.
7. Position the surge tank inlet hose clamp.
8. Connect the low coolant level switch electrical connector (3).
9. Install the surge tank overflow hose.
10. Install the air cleaner assembly.
11. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Reposition the surge tank inlet hose clamp from the radiator.
3. Remove the surge tank inlet hose from the radiator.
4. Reposition the surge tank inlet hose clamp at the surge tank.
5. Remove the surge tank inlet hose (1) from the surge tank.

1. Install the surge tank inlet hose (1) to the surge tank.
2. Position the surge tank inlet hose clamp to the surge tank.
3. Install the surge tank inlet hose to the radiator.
4. Position the surge tank inlet hose clamp to the radiator.
5. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

Surge Tank Hose/Pipe Replacement - Outlet (4.8L, 5.3L, and 6.0L Engines)

J 43181 Heater Line Quick Connect Release Tool

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Loosen the air cleaner outlet duct clamps at the following locations: Throttle body Mass airflow/intake air temperature (MAF/IAT) sensor
3. Remove the air cleaner outlet duct.
4. If equipped without regular production option (RPO) C36 auxiliary heater, remove the surge tank/heater outlet hose (1) from the mounting clip.
5. If equipped with RPO C36 auxiliary heater, remove the surge tank/heater outlet hose (1) from the mounting clip.
6. Install the J 43181 to the surge tank outlet hose.
7. Close the J 43181 around the surge tank outlet hose.
8. Firmly pull the J 43181 into the quick connect end of the outlet hose.
9. If equipped without RPO C36 auxiliary heater, firmly grasp the outlet hose. Pull the outlet hose in order to disengage the hose from the heater and blower module.
10. If equipped with RPO C36 auxiliary heater, firmly grasp the outlet hose. Pull the outlet hose in order to disengage the hose from the heater and blower module.
11. Reposition the surge tank outlet hose clamp at the surge tank.
12. Remove the surge tank outlet hose (2) from the surge tank.
13. Reposition the surge tank outlet hose clamp at the water pump.
14. Remove the surge tank outlet hose from the water pump.
15. Remove the surge tank outlet hose.

1. Install the surge tank outlet hose.
2. Install the surge tank outlet hose to the water pump.
3. Position the surge tank outlet hose clamp to the water pump.
4. Install the surge tank outlet hose (2) to the surge tank.
5. Position the surge tank outlet hose clamp to the surge tank.
6. If equipped with RPO C36 auxiliary heater, connect the surge tank outlet hose to the heater and blower module.
7. If equipped without RPO C36 auxiliary heater, connect the surge tank outlet hose to the heater and blower module. Firmly push the hose onto the heater and blower module pipe until an audible click is heard.
8. If equipped with RPO C36 auxiliary heater, install the surge tank/heater outlet hose (1) to the mounting clip.
9. If equipped without RPO C36 auxiliary heater, install the surge tank/heater outlet hose (1) to the mounting clip.
10. Install the air cleaner outlet duct.
11. Tighten the air cleaner outlet duct clamps at the following locations: Throttle body MAF/IAT sensor Tighten: Tighten the air cleaner outlet duct clamp screws to 7 N.m (62 lb in).
12. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Loosen the air cleaner outlet duct clamps at the following locations: Throttle body Mass airflow/intake air temperature (MAF/IAT) sensor
3. Remove the air cleaner outlet duct.
4. If necessary, remove the engine sight shield. Refer to «ENGINE SIGHT SHIELD REPLACEMENT (4.8L, 5.3L, 6.0L (LQW4))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) or «ENGINE SIGHT SHIELD REPLACEMENT (6.0L (LQ9))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
5. Remove the radiator vent inlet hose from the radiator inlet hose clips.
6. Reposition the inlet hose clamp from the radiator.
7. Remove the inlet hose from the radiator.
8. Remove the inlet hose clip from the fan shroud.
9. Reposition the inlet hose clamp from the water outlet.
10. Remove the inlet hose from the water outlet.

1. Install the inlet hose to the water outlet.
2. Reposition the inlet hose clamp to the water outlet.
3. Install the inlet hose clip to the fan shroud.
4. Install the inlet hose to the radiator.
5. Reposition the inlet hose clamp to the radiator.
6. Install the radiator vent inlet hose to the radiator inlet hose clips.
7. If necessary, install the engine sight shield. Refer to «ENGINE SIGHT SHIELD REPLACEMENT (4.8L, 5.3L, 6.0L (LQ4))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) or «ENGINE SIGHT SHIELD REPLACEMENT (6.0L (LQ9))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
8. Install the air cleaner outlet duct.
9. Tighten the air cleaner outlet duct clamps at the following locations: Throttle body MAF/IAT sensor Tighten: Tighten the air cleaner outlet duct clamp screws to 7 N.m (62 lb in).
10. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Reposition the inlet hose clamp from the radiator.
3. Remove the inlet hose from the radiator.
4. Reposition the inlet hose clamp from the water outlet.
5. Remove the inlet hose from the water outlet.

1. Install the inlet hose to the water outlet.
2. Reposition the inlet hose clamp to the water outlet.
3. Install the inlet hose to the radiator.
4. Reposition the inlet hose clamp to the radiator.
5. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Loosen the air cleaner outlet duct clamps at the following locations: Throttle body Mass airflow/intake air temperature (MAF/IAT) sensor
3. Remove the air cleaner outlet duct.
4. Reposition the outlet hose clamp from the water pump.
5. Remove the outlet hose from the water pump.
6. Reposition the outlet hose clamp from the radiator.
7. Remove the outlet hose from the radiator.

1. Install the outlet hose to the radiator.
2. Reposition the outlet hose clamp to the radiator.
3. Install the outlet hose to the water pump.
4. Reposition the outlet hose clamp to the water pump.
5. Install the air cleaner outlet duct.
6. Install the radiator inlet hose clip to the outlet duct.
7. Tighten the air cleaner outlet duct clamps at the following locations: Throttle body MAF/IAT sensor Tighten: Tighten the air cleaner outlet duct clamp screws to 7 N.m (62 lb in).
8. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Reposition the outlet hose clamp from the radiator.
3. Remove the radiator outlet hose from the radiator.
4. Reposition the surge tank outlet hose clamp from the surge tank.
5. Remove the surge tank outlet hose (2) from the surge tank.
6. Reposition the outlet hose clamp from the water pump.
7. Remove the outlet hose from the water pump.

1. Install the outlet hose to the water pump.
2. Reposition the outlet hose clamp to the water pump.
3. Install the surge tank outlet hose (2) to the surge tank.
4. Reposition the surge tank outlet hose clamp to the surge tank.
5. Install the radiator outlet hose to the radiator.
6. Reposition the outlet hose clamp to the radiator.
7. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Reposition the vent inlet hose clamp from the radiator.
3. Remove the vent inlet hose from the radiator.
4. Reposition the vent inlet hose clamp from the surge tank.
5. Remove the vent inlet hose from the surge tank.

1. Install the vent inlet hose to the surge tank.
2. Reposition the vent inlet hose clamp to the surge tank.
3. Install the vent inlet hose to the radiator.
4. Reposition the vent inlet hose clamp to the radiator.
5. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Disengage the plastic caps from the quick connect fittings. Pull the caps back along the pipe.
2. Using a bent-tip screwdriver or equivalent, pull on one of the open ends of the retaining ring in order to rotate the retaining ring.
3. Rotate the retaining ring around the quick connector until the retaining ring is out of position and can be completely removed. Discard the retaining rings.
4. Remove the engine oil cooler line from the quick connector fitting at the radiator. Pull the lines straight out from the connectors.
5. Clean all of the components in a suitable solvent, and dry them with compressed air.
6. Inspect the fittings, the connectors, the cooler lines, and the cooler for damage, distortion, or restriction. Replace parts as necessary.

1. Install a new retaining ring into each quick connector fitting.
2. Hook one of the open ends of the retaining ring in one of the slots in the quick connector.
3. Rotate the retaining ring around the connector until the retaining ring is positioned with all 3 ears through the 3 slots.
4. Ensure the 3 retaining ring ears can be seen from the inside of the connector and the retaining ring can move freely in the slots.
5. Install the engine oil cooler line into the quick connector fitting until a click is heard or felt. Pull back on the engine oil cooler lines to ensure a proper connection.
6. Snap the plastic cap onto the quick connect fitting.
7. Ensure that the plastic cap is fully seated against the fitting.
8. Ensure that no gap is present between the cap and the fitting.
9. Inspect and fill the engine oil to the proper level.

The optional oil cooler is either an integral part of the radiator or a separate unit placed in front of the radiator. The cooler lines and hoses are serviceable.

1. Disconnect the engine oil cooler quick connect fittings. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. If equipped with a 5.3L, or 6.0L engine, perform the following: Open the oil cooler hose clip located on the lower fan shroud. Remove the oil cooler hoses from the clip. Gently pull the oil cooler pipe fittings straight out from the radiator quick connect fittings.
3. If equipped with a 8.1L engine, remove the oil cooler hoses from the clip
4. Raise and suitably support the vehicle. Refer to «LIFTING & JACKING THE VEHICLE»(/gmc/yukon-denali/gmt800-1999-2006/remont/hoistjack/#lifting-jacking-the-vehicle) .
5. If equipped, remove the engine shield bolts.
6. Remove the engine shield.
7. If equipped with a 5.3L, or 6.0L engine, perform the following: Remove the oil cooler hose bracket bolt (1). Remove the oil cooler hose adapter bolts (2). Remove the oil cooler hose assembly and gasket. Discard the gasket. Inspect the fittings, connectors and cooler hoses for damage or distortion.
8. If equipped with a 8.1L engine, perform the following: Remove the oil cooler hose bracket bolt. Disconnect the quick connect fittings (1) at the engine. Remove the oil cooler hose assembly. Discard the gasket. Inspect the fittings, connectors and cooler hoses for damage or distortion.

1. If equipped with a 8.1L engine, perform the following: Remove the oil cooler hose assembly. Connect the quick connect fittings (1) at the engine. NOTE: Refer to «FASTENER NOTICE»(/gmc/yukon-denali/gmt800-1999-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) . Install the oil cooler hose bracket bolt. Tighten: Tighten the bolt to 50 N.m (37 lb ft).
2. If equipped with a 5.3L, or 6.0L engine, perform the following: Install the oil cooler hose assembly and a new gasket. Install the oil cooler hose adapter bolts (2). Tighten: Tighten the bolts to 12 N.m (106 lb in). Install the oil cooler hose bracket bolt (1). Tighten: Tighten the bolt to 25 N.m (18 lb ft).
3. If equipped, install the engine shield.
4. Install the engine shield bolts. Tighten: Tighten the bolts to 20 N.m (15 lb ft).
5. Lower the vehicle.
6. If equipped with a 5.3L, or 6.0L engine, perform the following: Install the oil cooler hoses to the hose clip on the fan shroud. Snap the oil cooler hose clip shut.
7. If equipped with a 8.1L engine, install the oil cooler hoses to the clip.
8. Connect the engine oil cooler quick connect fittings. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

The optional oil cooler is either an integral part of the radiator or a separate unit placed in front of the radiator. The cooler lines and hoses are serviceable.

1. Disconnect the engine oil cooler quick connect fittings. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. If equipped with a 5.3L or 6.0L engine, perform the following: Open the oil cooler hose clip located on the lower fan shroud. Remove the oil cooler hoses from the clip.
3. If equipped with a 8.1L engine, remove the oil cooler hoses from the clip.
4. Raise and suitably support the vehicle. Refer to «LIFTING & JACKING THE VEHICLE»(/gmc/yukon-denali/gmt800-1999-2006/remont/hoistjack/#lifting-jacking-the-vehicle) .
5. Place jack or utility stands at the rear of the vehicle.
6. If equipped, remove the engine protection shield. Refer to «ENGINE PROTECTION SHIELD REPLACEMENT»(/gmc/yukon-denali/gmt800-1999-2006/remont/frames-subframes-crossmembers/#frame-underbody) .
7. If equipped, remove the front differential carrier shield. Refer to «SHIELD REPLACEMENT»(/gmc/yukon-denali/gmt800-1999-2006/remont/differentials-drive-axles/#drive-axles-front) .
8. Place an adjustable jack under the front differential carrier.
9. Remove the inner axle housing nuts and washers from the bracket.
10. Remove the differential carrier upper mounting bolt and nut.
11. Pivot the differential carrier forward and down on the lower mount bolt while it is being supported by the adjustable jack.
12. Secure the differential carrier to the jack.
13. Remove the differential carrier lower mounting bolt and nut.
14. Lower the jack 4 to 6 inches.
15. If equipped with a 5.3L or 6.0L engine, perform the following: Remove the oil cooler hose bracket bolt (1). Remove the oil cooler hose adapter bolts (2). Remove the oil cooler hose assembly and gasket. Discard the gasket. Inspect the fittings, connectors and cooler hoses for damage or distortion.
16. If equipped with a 8.1L engine, perform the following: Remove the oil cooler hose bracket bolt. Disconnect the quick connect fittings (1) at the engine. Remove the oil cooler hose assembly. Discard the gasket. Inspect the fittings, connectors and cooler hoses for damage or distortion.

1. If equipped with a 8.1L engine, perform the following: Install the oil cooler hose assembly and a NEW gasket. Connect the quick connect fittings (1) at the engine. NOTE: Refer to «FASTENER NOTICE»(/gmc/yukon-denali/gmt800-1999-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) . Install the oil cooler hose bracket bolt. Tighten: Tighten the bolt to 50 N.m (37 lb ft).
2. If equipped with a 5.3L or 6.0L engine, perform the following: Install the oil cooler hose assembly and a NEW gasket. Install the oil cooler hose adapter bolts (2). Tighten: Tighten the bolts to 12 N.m (106 lb in). Install the oil cooler hose bracket bolt (1). Tighten: Tighten the bolt to 25 N.m (18 lb ft).
3. Raise the jack in order to position the differential carrier.
4. Install the differential carrier lower mounting bolt and nut. Do not tighten the bolt at this time.
5. Pivot the differential carrier up and back on the lower mount bolt while it is being supported by the jack.
6. Install the differential carrier upper mounting bolt and nut. Do not tighten the bolt at this time.
7. Install the inner axle housing washers and nuts to the brackets. Tighten: The inner axle housing bolts to 100 N.m (75 lb ft). The upper and lower differential carrier bolts to 100 N.m (75 lb ft).
8. Remove the adjustable jack from under the front differential carrier.
9. If equipped, install the front differential carrier shield. Refer to «SHIELD REPLACEMENT»(/gmc/yukon-denali/gmt800-1999-2006/remont/differentials-drive-axles/#drive-axles-front) .
10. If equipped, install the engine protection shield. Refer to «ENGINE PROTECTION SHIELD REPLACEMENT»(/gmc/yukon-denali/gmt800-1999-2006/remont/frames-subframes-crossmembers/#frame-underbody) .
11. Remove the jack or utility stands from the rear of the vehicle.
12. Lower the vehicle.
13. If equipped with a 8.1L engine perform the following
14. Install the oil cooler hoses to the clip.
15. If equipped with a 5.3L or 6.0L engine, perform the following: Install the oil cooler hoses to the hose clip on the fan shroud. Snap the oil cooler hose clip shut.
16. Connect the engine oil cooler quick connect fittings. Refer to «Engine Oil Cooler Pipe/Hose Quick Connect Fitting»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

Fan Replacement

Tools Required

1. J 46406 Fan Clutch Remover and Installer
2. J 41240-5A Fan Clutch Wrench

1. Remove the upper fan shroud. Refer to «FAN SHROUD REPLACEMENT - Upper (W/O M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «FAN SHROUD REPLACEMENT - Upper (W/M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Install the J 46406 and the J 41240-5A to the fan clutch.
3. Remove the fan hub nut from the water pump in a counterclockwise rotation.
4. Lay the fan blade face down on a workbench.
5. Remove the fan clutch bolts from the rear of the fan blade, if necessary.
6. Separate the fan clutch from the fan blade.

1. Install the fan clutch bolts.
2. Install the fan clutch onto the fan blade, if necessary. NOTE: Refer to «FASTENER NOTICE»(/gmc/yukon-denali/gmt800-1999-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) .
3. Install the fan clutch bolts. Tighten: Tighten the bolts to 23 N.m (17 lb ft).
4. Install the fan blade.
5. Install the J 46406 and the J 41240-5A to the fan clutch. Tighten: Tighten the fan clutch nut clockwise to 56 N.m (41 lb ft).
6. Install the upper fan shroud. Refer to «FAN SHROUD REPLACEMENT - Upper (W/O M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «FAN SHROUD REPLACEMENT - Upper (W/M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

Fan Clutch Replacement

Tools Required

1. J 46406 Fan Clutch Remover and Installer
2. J 41240-5A Fan Clutch Wrench

1. Remove the upper fan shroud. Refer to «FAN SHROUD REPLACEMENT - Upper (W/O M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «FAN SHROUD REPLACEMENT - Upper (W/M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Install the J 46406 and the J 41240-5A to the fan clutch.
3. Remove the fan hub nut from the water pump in a counterclockwise rotation.
4. Lay the fan blade face down on a workbench.
5. Remove the fan clutch bolts from the rear of the fan blade.
6. Separate the fan clutch from the fan blade.

1. Install the fan clutch bolts.
2. Install the fan clutch onto the fan blade. NOTE: Refer to «FASTENER NOTICE»(/gmc/yukon-denali/gmt800-1999-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) .
3. Install the fan clutch bolts. Tighten: Tighten the bolts to 23 N.m (17 lb ft).
4. Install the fan blade.
5. Install the J 46406 and the J 41240-5A to the fan clutch. Tighten: Tighten the fan clutch nut clockwise to 56 N.m (41 lb ft).
6. Install the upper fan shroud. Refer to «FAN SHROUD REPLACEMENT - Upper (W/O M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «FAN SHROUD REPLACEMENT - Upper (W/M74)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Remove the radiator outlet hose. Refer to «RADIATOR HOSE REPLACEMENT - Inlet (4.8L, 5.3L, and 6.0L Engines)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «RADIATOR HOSE REPLACEMENT - Inlet (8.1L Engine)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the water pump inlet bolts.
3. Remove the water pump inlet and thermostat from the water pump.

1. Install the thermostat and water pump inlet to the water pump.
2. Install the water pump inlet bolts. Tighten: Tighten the water pump inlet bolts to 15 N.m (11 lb ft).
3. Install the radiator outlet hose. Refer to «RADIATOR HOSE REPLACEMENT - Inlet (4.8L, 5.3L, and 6.0L Engines)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «RADIATOR HOSE REPLACEMENT - Inlet (8.1L Engine)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Reposition the inlet hose clamp at the water outlet.
3. Remove the inlet hose from the water outlet.
4. Remove the water outlet bolts (2).
5. Remove the water outlet (1).
6. Remove the thermostat (3).

1. Install the thermostat (3).
2. Install the water outlet (1). NOTE: Refer to «FASTENER NOTICE»(/gmc/yukon-denali/gmt800-1999-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) .
3. Install the water outlet bolts (2). Tighten: Tighten the water outlet bolts to 30 N.m (22 lb ft).
4. Install the inlet hose to the water outlet.
5. Position the inlet hose clamp at the water outlet.
6. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the drive belt tensioner. Refer to «DRIVE BELT TENSIONER REPLACEMENT -- ACCESSORY»(ref-176772-S20278798422005051100000) .
3. Reposition the inlet hose clamp at the water crossover.
4. Remove the inlet hose from the water crossover.
5. Reposition the heater inlet hose clamp at the water crossover.
6. Remove the heater inlet hose from the water crossover.
7. Reposition the bypass hose clamps at the water crossover and water pump.
8. Remove the bypass hose.
9. Remove the generator. Refer to «GENERATOR (4.8L, 5.3L & 6.0L ENGINES)»(/gmc/yukon-denali/gmt800-1999-2006/remont/charging-system/#charging-system) or «GENERATOR (8.1L ENGINE)»(/gmc/yukon-denali/gmt800-1999-2006/remont/charging-system/#charging-system) .
10. Remove the power steering pump. Refer to «POWER STEERING PUMP REPLACEMENT (4.8 L, 5.3 L, & 6.0L)»(/gmc/yukon-denali/gmt800-1999-2006/remont/manual-power-steering/#power-steering-system) or «POWER STEERING PUMP REPLACEMENT (8.1 L)»(/gmc/yukon-denali/gmt800-1999-2006/remont/manual-power-steering/#power-steering-system) .
11. Remove the generator bracket bolts and nut.
12. Remove the generator bracket stud.
13. Remove the generator bracket.
14. Remove the water crossover bolts.
15. Remove the water crossover.
16. Remove and discard the water crossover gaskets.
17. If replacing the water crossover remove the following: Water outlet bolts (2) Water outlet (1) Thermostat (3)

1. If replacing the water crossover install the following: Thermostat (3) Water outlet (1) Water outlet bolts (2) Tighten: Tighten the water outlet bolts to 30 N.m (22 lb ft).
2. Install NEW water crossover gaskets.
3. Install the water crossover.
4. Install the water crossover bolts. Tighten: Tighten the water crossover bolts to 50 N.m (37 lb ft).
5. Install the generator bracket.
6. Install the generator bracket stud. Tighten: Tighten the generator bracket stud to 20 N.m (15 lb ft).
7. Install the generator bracket bolts and nut. Tighten: Tighten the generator bracket bolts and nut to 50 N.m (37 lb ft).
8. Install the power steering pump. Refer to «POWER STEERING PUMP REPLACEMENT (4.8 L, 5.3 L, & 6.0L)»(/gmc/yukon-denali/gmt800-1999-2006/remont/manual-power-steering/#power-steering-system) or «POWER STEERING PUMP REPLACEMENT (8.1 L)»(/gmc/yukon-denali/gmt800-1999-2006/remont/manual-power-steering/#power-steering-system) .
9. Install the generator. Refer to «GENERATOR (4.8L, 5.3L & 6.0L ENGINES)»(/gmc/yukon-denali/gmt800-1999-2006/remont/charging-system/#charging-system) or «GENERATOR (8.1L ENGINE)»(/gmc/yukon-denali/gmt800-1999-2006/remont/charging-system/#charging-system) .
10. Install the bypass hose.
11. Position the bypass hose clamps at the water crossover and water pump.
12. Install the heater inlet hose to the water crossover.
13. Position the heater inlet hose clamp at the water crossover.
14. Install the inlet hose to the water crossover.
15. Position the inlet hose clamp at the water crossover.
16. Install the drive belt tensioner. Refer to «DRIVE BELT TENSIONER REPLACEMENT -- ACCESSORY»(ref-176772-S20278798422005051100000) .
17. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the coolant air bleed pipe studs (1).
3. Remove the coolant air bleed pipe (2) with gaskets (3).
4. Remove the coolant air bleed pipe cover bolts (1) and covers (2).
5. Remove the gaskets from the coolant air bleed pipe and covers.
6. Discard the gaskets.
7. Remove the coolant air bleed hose (1) from the pipe (2).

1. Install the coolant air bleed hose (1) onto the pipe (2).
2. Install the gaskets onto the coolant air bleed pipe and covers.
3. Install the coolant air bleed pipe (2) and gaskets (3) onto the cylinder heads.
4. Install the coolant air bleed pipe studs (1). Tighten: Tighten the coolant air bleed pipe studs to 12 N.m (106 lb in).
5. Install the coolant air bleed pipe covers (2) and bolts (1). Tighten: Tighten the coolant air bleed pipe cover bolts to 12 N.m (106 lb in).
6. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. If necessary, remove the engine sight shield. Refer to «ENGINE SIGHT SHIELD REPLACEMENT (4.8L, 5.3L, 6.0L (LQ4))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) or «ENGINE SIGHT SHIELD REPLACEMENT (6.0L (LQ9))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
2. Reposition the coolant air bleed hose clamp at the throttle body.
3. Remove the coolant air bleed hose from the throttle body.
4. Reposition the hose clamp at the pipe.
5. Remove the coolant air bleed hose (1) from the pipe (2).

1. Install the coolant air bleed hose (1) to the pipe (2).
2. Position the hose clamp at the pipe.
3. Install the coolant air bleed hose to the throttle body.
4. Position the coolant air bleed hose clamp at the throttle body.
5. If necessary, install the engine sight shield. Refer to «ENGINE SIGHT SHIELD REPLACEMENT (4.8L, 5.3L, 6.0L (LQ4))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) or «ENGINE SIGHT SHIELD REPLACEMENT (6.0L (LQ9))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
6. Add engine coolant, if necessary.

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Loosen the air cleaner outlet duct clamps at the following locations: Throttle body Mass airflow/intake air temperature (MAF/IAT) sensor
3. Remove the radiator inlet hose clip from the outlet duct.
4. Remove the air cleaner outlet duct.
5. If necessary, remove the engine sight shield. Refer to «ENGINE SIGHT SHIELD REPLACEMENT (4.8L, 5.3L, 6.0L (LQ4))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) or «ENGINE SIGHT SHIELD REPLACEMENT (6.0L (LQ9))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
6. Remove the radiator vent inlet hose from the radiator hose clips.
7. Reposition the inlet hose clamp at the water pump.
8. Remove the inlet hose from the water pump.
9. Remove the fan blade. Refer to «Fan Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement) .
10. Remove the accessory drive belt. Refer to «DRIVE BELT REPLACEMENT -- ACCESSORY»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
11. Reposition the outlet hose clamp at the water pump.
12. Remove the outlet hose from the water pump.
13. Reposition the surge tank outlet hose clamp at the water pump.
14. Remove the surge tank outlet hose from the water pump.
15. Reposition the heater inlet hose clamp at the water pump.
16. Remove the heater inlet hose from the water pump.
17. Remove the water pump bolts.
18. Remove the water pump and gaskets.
19. Discard the water pump gaskets.

1. Install the water pump and NEW gaskets.
2. Install the water pump bolts. Tighten: Tighten the water pump bolts a first pass to 15 N.m (11 lb ft). Tighten the water pump bolts a final pass to 30 N.m (22 lb ft).
3. Install the heater inlet hose to the water pump.
4. Position the heater inlet hose clamp at the water pump.
5. Install the surge tank outlet hose to the water pump.
6. Position the surge tank outlet hose clamp at the water pump.
7. Install the outlet hose to the water pump.
8. Position the outlet hose clamp at the water pump.
9. Install the accessory drive belt. Refer to «DRIVE BELT REPLACEMENT -- ACCESSORY»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
10. Install the fan blade. Refer to «Fan Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement) .
11. Install the inlet hose to the water pump.
12. Position the inlet hose clamp at the water pump.
13. Install the engine vent inlet hose to the radiator hose clips.
14. If necessary, install the engine sight shield. Refer to «ENGINE SIGHT SHIELD REPLACEMENT (4.8L, 5.3L, 6.0L (LQ4))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) or «ENGINE SIGHT SHIELD REPLACEMENT (6.0L (LQ9))»(/gmc/yukon-denali/gmt800-1999-2006/remont/mechanical/#engine-mechanical-48l-53l-60l-on-vehicle-suv) .
15. Install the air cleaner outlet duct.
16. Install the radiator inlet hose clip to the outlet duct.
17. Tighten the air cleaner outlet duct clamps at the following locations: Throttle body MAF/IAT sensor Tighten: Tighten the air cleaner outlet duct clamp screws to 7 N.m (62 lb in).
18. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the drive belt. Refer to «DRIVE BELT TENSIONER REPLACEMENT -- ACCESSORY»(ref-176772-S20278798422005051100000) .
3. Remove the fan clutch. Refer to «Fan Clutch Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement) .
4. Reposition the outlet hose clamp at the water pump.
5. Remove the outlet hose from the water pump.
6. Reposition the bypass hose clamps at the water pump and water crossover.
7. Remove the bypass hose.
8. Remove the water pump bolts.
9. Remove the water pump.
10. Remove and discard the water pump gaskets.

1. Place NEW water pump gaskets into place.
2. Install the water pump. NOTE: Refer to «FASTENER NOTICE»(/gmc/yukon-denali/gmt800-1999-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) .
3. Install the water pump bolts. Tighten: Tighten the water pump bolts to 50 N.m (37 lb ft).
4. Install the bypass hose.
5. Position the bypass hose clamps at the water pump and water crossover.
6. Install the outlet hose to the water pump.
7. Position the outlet hose clamp at the water pump.
8. Install the fan clutch. Refer to «Fan Clutch Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__fan-clutch-replacement) .
9. Install the drive belt. Refer to «DRIVE BELT REPLACEMENT -- ACCESSORY»(ref-176772-S04987143402005051100000) .
10. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the radiator drain cock.

1. Install the radiator drain cock.
2. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Loosen the air cleaner outlet duct clamps from the throttle body.
2. Loosen the air cleaner outlet duct clamps from the mass airflow sensor.
3. Remove the air cleaner outlet duct.
4. If equipped remove the throttle body heater hose retainer from the fan shroud.
5. If equipped remove the inlet radiator hose retainer from the fan shroud.
6. Remove the fan shroud retainers.
7. Remove the fan shroud bolts
8. Remove the upper fan shroud.

1. Install the upper fan shroud.
2. Install the fan shroud bolts. Tighten: Tighten the bolts to 9 N.m (80 lb in).
3. Install the fan shroud retainers.
4. If equipped install the inlet radiator hose retainer to the fan shroud
5. If equipped install the throttle body heater hose retainer to the fan shroud.
6. Install the air cleaner outlet duct.
7. Tighten the air cleaner outlet duct clamp at the throttle body. Tighten: Tighten the clamp screw to 7 N.m (62 lb in).
8. Tighten the air cleaner outlet duct clamp at the mass airflow sensor. Tighten: Tighten the clamp screw to 7 N.m (62 lb in).

1. Loosen the air cleaner outlet duct clamps from the throttle body.
2. Loosen the air cleaner outlet duct clamps from the mass airflow sensor.
3. Remove the air cleaner outlet duct.
4. Remove the A/C line retainer from the fan shroud.
5. Remove the engine harness clip from the PCM cover.
6. Remove the TCM cover bolts.
7. Remove TCM cover from the fan shroud.
8. Loosen the TCM electrical connector bolts.
9. Disconnect the TCM electrical connectors (1).
10. Remove the TCM and cover.
11. Remove the fan shroud retainers.
12. Remove the fan shroud bolts
13. Remove the upper fan shroud.

1. Install the upper fan shroud.
2. Install the fan shroud bolts. Tighten: Tighten the bolts to 9 N.m (80 lb in).
3. Install the fan shroud retainers.
4. Connect the TCM electrical connectors (1).
5. Install the TCM and cover.
6. Tighten the TCM electrical connector bolts. Tighten: Tighten the bolts to 8 N.m (71 lb in).
7. Install the TCM cover to the fan shroud.
8. Install the TCM cover bolts. Tighten: Tighten the bolts to 9 N.m (80 lb in).
9. Install the engine harness clip to the PCM cover.
10. Install the A/C line retainer to the fan shroud.
11. Install the air cleaner outlet duct.
12. Tighten the air cleaner outlet duct clamp at the throttle body. Tighten: Tighten the clamp screws to 7 N.m (62 lb in).
13. Tighten the air cleaner outlet duct clamp at the mass airflow sensor. Tighten: Tighten the clamp screws to 7 N.m (62 lb in).

1. Remove the cooling fan. Refer to «Fan Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement) .
2. If equipped with engine oil cooler, remove the oil cooler hose clip from the lower fan shroud.
3. Lift the lower fan shroud up in order to disengage the fan shroud from the retaining clips on the radiator.

1. Install the lower fan shroud to the retaining clips on the radiator and firmly push down.
2. If equipped with the engine oil cooler, Install the oil cooler hose clip to the lower fan shroud.
3. Install the cooling fan. Refer to «Fan Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system__fan-replacement)

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system)
2. Reposition the inlet hose clamp from the radiator.
3. Remove the inlet hose from the radiator.
4. Reposition the outlet hose clamp from the radiator.
5. Remove the radiator outlet hose from the radiator.
6. Remove the lower fan shroud. Refer to «FAN SHROUD REPLACEMENT - Lower»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
7. Reposition the radiator vent inlet hose clamp from the radiator.
8. Remove the vent inlet hose from the radiator.
9. Remove the engine oil cooler lines from the radiator. Refer to «Engine Oil Cooler Hose/Pipe Replacement (2WD)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «Engine Oil Cooler Hose/Pipe Replacement (4WD)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
10. Remove the transmission oil cooler lines from the radiator. Refer to «TRANSMISSION OIL COOLER LINES»(/gmc/yukon-denali/gmt800-1999-2006/remont/automatic-trans/#automatic-transmission-servicing-except-allison) .
11. Remove the radiator bolts.
12. Remove the radiator from the vehicle.

1. Install the radiator to the vehicle.
2. Install the radiator bolts. Tighten: Tighten the bolts to 25 N.m (18 lb ft).
3. Install the engine oil cooler lines to the radiator. Refer to «Engine Oil Cooler Hose/Pipe Replacement (2WD)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) or «Engine Oil Cooler Hose/Pipe Replacement (4WD)»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Install the transmission oil cooler lines to the radiator. Refer to «TRANSMISSION OIL COOLER LINES»(/gmc/yukon-denali/gmt800-1999-2006/remont/automatic-trans/#automatic-transmission-servicing-except-allison) .
5. Install the radiator vent inlet hose to the radiator.
6. Reposition the radiator vent inlet hose clamp to the radiator.
7. Install the lower fan shroud. Refer to «FAN SHROUD REPLACEMENT - Lower»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
8. Install the outlet hose to the radiator.
9. Reposition the outlet hose clamp to the radiator.
10. Install the inlet hose to the radiator.
11. Reposition the inlet hose clamp to the radiator.
12. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system)

1. Remove the radiator. Refer to «Radiator Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system)
2. Remove the radiator air baffle retainers.
3. Remove the radiator air baffles.

1. Install the radiator air baffles.
2. Install the radiator air baffle retainers.
3. Install the radiator. Refer to «Radiator Replacement»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Remove the radiator air upper baffle retainers.
2. Remove the radiator air upper baffle.

1. Install the radiator air upper baffle.
2. Install the radiator air upper baffle retainers.

Dealer Installation Only

1. Drain the cooling system/engine block. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Raise and suitably support the vehicle. Refer to «LIFTING & JACKING THE VEHICLE»(/gmc/yukon-denali/gmt800-1999-2006/remont/hoistjack/#lifting-jacking-the-vehicle) .
3. Remove the oil pan skid plate bolts and plate.
4. Remove the oil cooler hose bracket bolt (1).
5. Remove the oil cooler hose adapter bolts (2).
6. Remove and discard the oil cooler hose adapter gasket.
7. Position the oil cooler hose adapter end out of the way.
8. Install the coolant heater in place of the drain plug. Tighten: Tighten the coolant heater to 50 N.m (37 lb ft).
9. Push the engine coolant heater cord electrical connector (2) firmly into the coolant heater (1).
10. Place the cord into position.
11. Install the heater cord bolt and retainer. Tighten: Tighten the heater cord bolt to 8 N.m (71 lb in).
12. Position the oil cooler hose adapter.
13. Install a NEW oil cooler hose adapter gasket.
14. Install the oil cooler hose adapter bolts (2). Tighten: Tighten the oil cooler hose adapter bolts to 12 N.m (106 lb in).
15. Install the oil cooler hose bracket bolt (1). Tighten: Tighten the oil cooler hose bracket bolt to 25 N.m (18 lb ft).
16. Install the oil pan skid plate and bolts. Tighten: Tighten the oil pan skid plate bolts to 20 N.m (15 lb ft).
17. Lower the vehicle.
18. Fill the cooling system/engine block. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system/engine block. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Raise and suitably support the vehicle. Refer to «LIFTING & JACKING THE VEHICLE»(/gmc/yukon-denali/gmt800-1999-2006/remont/hoistjack/#lifting-jacking-the-vehicle) .
3. Remove the oil pan skid plate bolts and plate.
4. Remove the oil cooler hose bracket bolt (1).
5. Remove the oil cooler hose adapter bolts (2).
6. Remove and discard the oil cooler hose adapter gasket.
7. Position the oil cooler hose adapter end out of the way.
8. Disconnect the coolant heater electrical connector (2).
9. Remove the coolant heater from the engine block.
10. Remove any burrs, sealer, or other rough spots.

1. If reusing the old coolant heater, apply thread sealant GM P/N 12346004 (Canadian P/N 10953480) or equivalent to the threads.
2. Install the coolant heater to the engine block. Tighten: Tighten the coolant heater to 50 N.m (37 lb ft).
3. Connect the coolant heater electrical connector (2).
4. Position the oil cooler hose adapter end.
5. Install a NEW oil cooler hose adapter gasket.
6. Install the oil cooler hose adapter bolts (2). Tighten: Tighten the oil cooler hose adapter bolts to 12 N.m (106 lb in).
7. Install the oil cooler hose bracket bolt (1). Tighten: Tighten the oil cooler hose bracket bolt to 25 N.m (18 lb ft).
8. Install the oil pan skid plate and bolts. Tighten: Tighten the oil pan skid plate bolts to 20 N.m (15 lb ft).
9. Lower the vehicle.
10. Fill the cooling system/engine block. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Drain the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Disconnect the block heater cord from the block heater.
3. Remove the engine block heater.

1. Apply sealant GM P/N 12346004, Canadian P/N 10953480 or equivalent to the threads of the engine block heater.
2. Install the engine block heater into the block. Tighten: Tighten the engine block heater to 60 N.m (40 lb ft).
3. Connect the block heater cord to the block heater.
4. Fill the cooling system. Refer to «Draining and Filling Cooling System»(/gmc/yukon-denali/gmt800-1999-2006/remont/cooling-system-mechanical/#engine-cooling-system) .

1. Raise and suitably support the vehicle. Refer to «LIFTING & JACKING THE VEHICLE»(/gmc/yukon-denali/gmt800-1999-2006/remont/hoistjack/#lifting-jacking-the-vehicle) .
2. Disconnect the coolant heater electrical connector (2).
3. Remove the coolant heater cord retainer and bolts.
4. Remove the coolant heater cord.

Note. The heater cord must not touch the engine, hot pipes, manifold, or any moving parts. Route the cord to the left front of the engine compartment securing with tie straps as necessary to prevent damage.

1. Install the coolant heater cord.
2. Install the coolant heater cord bolts and retainer. Tighten: Tighten the coolant heater cord bolts to 8 N.m (71 lb in).
3. Connect the coolant heater electrical connector (2).
4. Lower the vehicle.

CHECK COOLANT TEMP

The instrument panel cluster (IPC) displays ENGINE COOLANT HOT message when the IPC receives a class 2 message from the powertrain control module (PCM) requesting illumination of this driver warning.

ENGINE OVERHEATED

The IPC displays ENGINE OVERHEATED message when the IPC receives a class 2 message from the PCM requesting illumination of this driver warning.

LOW COOLANT

The IPC displays LOW COOLANT LEVEL message when the IPC receives a class 2 message from the PCM requesting illumination of this driver warning.

REDUCED ENGINE POWER

The IPC displays REDUCED ENGINE POWER message when the IPC detects a reduced engine power condition from the PCM. The IPC receives a class 2 message from the PCM requesting illumination when the engine temperature reaches 132°C (270°F).

Cooling Fan Control - Two Fan System

The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

The PCM commands the low speed cooling fans ON under the following conditions

1. Engine coolant temperature exceeds approximately 94.5°C (202°F).
2. A/C refrigerant pressure exceeds 1447 kPa (210 psi).
3. After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 101°C (214°F) the low speed fans will run for a minimum of 60 seconds After 60 seconds, if the coolant temperature drops below 101°C (214°F) the fans will shut OFF. The fans will automatically shut OFF after 3 min. regardless of coolant temperature.

The PCM commands the high speed fans ON under the following conditions

1. Engine coolant temperature exceeds approximately 104.25°C (220°F).
2. A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi).
3. When certain DTCs set.

At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed if required. This insures idle stability by preventing the fans from cycling between high and low speed.

Coolant Level Control

The engine cooling system contains an engine coolant level switch to alert the driver in the event of a coolant loss. The powertrain control module (PCM) sends out a coolant loss signal over the coolant level switch signal circuit. When the engine coolant level switch reads a low coolant level in the fill tank, the switch opens. The message center receives its power from engine wiring harness junction block on the battery positive voltage circuit. Ground is provided by the ground circuits via the body wiring harness junction block and the engine wiring harness junction block. The cluster receives the class 2 message from the PCM indicating Low Coolant and displays the LOW COOLANT LEVEL message on the driver information center (DIC).

Coolant Heater

The optional engine coolant heater (RPO K05) operates using 110-volt AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather 29°C (20°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. A weather shield on the cord is provided to protect the plug when not in use.

The cooling system's function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly.

Cooling Cycle

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. Coolant will then be pumped through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders, where it absorbs heat.

Some coolant is also pumped from the water pump to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost.

The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

Coolant is also directed to the throttle body. There it circulates through passages in the casting. During initial start up, the coolant assists in warming the throttle body. During normal operating temperatures, the coolant assists in regulating the throttle body temperature.

Cooling Cycle (6.6L Diesel Engine)

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. The coolant flows to the heater core while the engine is running. This provides the passenger compartment with heat and defrost.

Coolant is then pumped through the water pump outlet and through the coolant pipe to the engine oil cooler. The coolant flows around the oil cooler element and to the rear engine cover. The rear engine cover distributes the coolant flow to both banks of the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

Coolant is also directed to the turbocharger. There it circulates through passages in the center housing. During engine warm-up cycle the bypass valve located in the turbocharger inlet hose at the outlet pipe prevents coolant flow. During normal operating temperatures, the coolant assists in keeping the turbocharger cool.

From the cylinder heads, the coolant flows to the thermostats. The coolant flows from the thermostat housing to the water pump through the bypass pipe until the engine reaches 85°C (185°F).

Operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components

Coolant

The engine coolant is a solution made up of a 50-50 mixture of DEX-COOL and suitable drinking water. The coolant solution carries excess heat away from the engine to the radiator, where the heat is dissipated to the atmosphere.

Radiator

The radiator is a heat exchanger. It consists of a core and two tanks. The aluminum core is a tube and fin crossflow design that extends from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer to the atmosphere.

The inlet and outlet tanks are a molded, high temperature, nylon reinforced plastic material. A high temperature rubber gasket seals the tank flange edge to the aluminum core. The tanks are clamped to the core with clinch tabs. The tabs are part of the aluminum header at each end of the core.

The radiator also has a drain cock located in the bottom of the left hand tank. The drain cock unit includes the drain cock and drain cock seal.

The radiator removes heat from the coolant passing through it. The fins on the core transfer heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant.

Surge Tank

The surge tank is a plastic tank with a threaded pressure cap. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system that allows the coolant to expand and contract. The surge tank provides a coolant fill point and a central air bleed location.

During vehicle use, the coolant heats and expands. The increased coolant volume flows into the surge tank. As the coolant circulates, any air is allowed to bubble out. Coolant without air bubbles absorbs heat much better than coolant with bubbles.

Pressure Cap

The pressure cap seals the cooling system. It contains a blow off or pressure relief valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring, which protects the radiator from excessive cooling system pressure. The vacuum valve is held against its seat by a spring, which permits opening of the valve to relieve vacuum created in the cooling system as it cools off. The vacuum, if not relieved, might cause the radiator and/or coolant hoses to collapse.

The pressure cap allows cooling system pressure to build up as the temperature increases. As the pressure builds, the boiling point of the coolant increases. Engine coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat transfers from the radiator to the cooler, passing air.

The pressure in the cooling system can get too high. When the cooling system pressure exceeds the rating of the pressure cap, it raises the pressure valve, venting the excess pressure.

As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the surge tank. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator and coolant hoses from collapsing.

Cooling Fan and Clutch

The engine cooling fan and clutch are driven by the crankshaft via the drive belt. The cooling fan draws air through the radiator to improve the transfer of heat from the coolant to the atmosphere. As the fan blades spin, they pull cool, outside air past the radiator core. The fan clutch drives the cooling fan. The fan clutch controls the amount of torque that is transmitted from the crankshaft to the fan blades. The clutch allows more torque to engage on the fan when the engine operating temperature increases and/or the vehicle speed is low. As the torque increases, the fan turns more quickly. The fan clutch decreases the torque applied to the cooling fan when the engine temperature decreases and/or the vehicle speed is high. As the torque decreases, the fan speed decreases.

Air Baffles and Seals

The cooling system uses deflectors, air baffles and air seals to increase cooling system capability. Deflectors are installed under the vehicle to redirect airflow beneath the vehicle and through the radiator to increase engine cooling. Air baffles are also used to direct airflow through the radiator and increase cooling capability. Air seals prevent air from bypassing the radiator and A/C condenser, and prevent recirculation of hot air for better hot weather cooling and A/C condenser performance.

Water Pump

The water pump is a centrifugal vane impeller type pump. The pump consists of a housing with coolant inlet and outlet passages and an impeller. The impeller is mounted on the pump shaft and consists of a series of flat or curved blades or vanes on a flat plate. When the impeller rotates, the coolant between the vanes is thrown outward by centrifugal force.

The impeller shaft is supported by one or more sealed bearings. The sealed bearings never need to be lubricated. Grease cannot leak out, dirt and water cannot get in as long as the seal is not damaged or worn.

The purpose of the water pump is to circulate coolant throughout the cooling system. The water pump is driven by the crankshaft via the drive belt.

Water Pump (6.6L Diesel Engine)

The water pump is a centrifugal vane impeller type pump. The water pump is gear driven by the crankshaft gear. The pump consists of a housing with coolant inlet and outlet passages and an impeller. The impeller is a flat plate mounted on the pump shaft with a series of flat or curved blades or vanes. When the impeller rotates, the coolant between the vanes is thrown outward by centrifugal force. The impeller shaft is supported by bearings. Splash of the engine oil lubricates the bearings. The bearings and shaft are sealed to prevent engine oil to mix with the coolant. If the seal fails, coolant will leak out the vent hole in the water pump housing.

The purpose of the water pump is to circulate coolant throughout the cooling system.

Thermostat

The thermostat is a coolant flow control component. It's purpose is to help regulate the operating temperature of the engine. It utilizes a temperature sensitive wax-pellet element. The element connects to a valve through a small piston. When the element is heated, it expands and exerts pressure against the small piston. This pressure forces the valve to open. As the element is cooled, it contracts. This contraction allows a spring to push the valve closed.

When the coolant temperature is below the rated thermostat opening temperature, the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up. After the coolant temperature reaches the rated thermostat opening temperature, the thermostat valve will open. The coolant is then allowed to circulate through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a restriction in the cooling system, after it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.

Thermostats (6.6L Diesel Engine)

The thermostats are coolant flow control components. The purpose of the thermostats are to regulate the correct operating temperature of the engine. The thermostats utilizes a temperature sensitive wax-pellet element. The element connects to a valve through a piston. When the element is heated, it expands and exerts pressure against a rubber piston. This pressure forces the valve to open. As the element is cooled, it contracts. This contraction allows a spring to push the valve closed.

The 6.6L diesel engine requires two thermostats for correct coolant flow. The front thermostat is a dual purpose thermostat. The front thermostat controls the coolant flow to the bypass port and to the water outlet. The rear thermostat only controls the coolant flow to the water outlet.

When the coolant temperature is below the rated thermostat opening temperature, the front thermostat valve remains closed to the water outlet and is opened to the bypass port. The bottom portion of the thermostat is raised off of the bypass port while at the same time the top portion closes the coolant flow to the water outlet. The rear thermostat also is closed to the water outlet during engine warm-up. This prevents circulation of the coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 82°C (180°F) the front thermostat primary valve opening temperature, the front thermostat primary valve will start to open. The coolant is then allowed to circulate through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. As the engine coolant reaches 85°C (185°F) and more coolant demand is required the front thermostat secondary valve begins to close the bypass port and the rear thermostat begins to open coolant flow to the water outlet. The thermostats will continue to control the coolant flow by opening and closing. The front thermostat will be fully open when the coolant temperature reaches 95°C (203°F) the rear thermostat will be fully open when the coolant temperature reaches 100°C (212°F). The thermostat also provides a restriction in the cooling system, even after the it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.

Engine Oil Cooler

The engine oil cooler is a heat exchanger. It is located inside the left side end tank of the radiator. The engine oil temperature is controlled by the temperature of the engine coolant that surrounds the oil cooler in the radiator.

The engine oil pump, pumps the oil through the engine oil cooler line to the oil cooler. The oil then flows through the cooler where the engine coolant absorbs heat from the oil. The oil is then pumped through the oil cooler return line, to the oil filter, to the engine block oil system.

Engine Oil Cooler (6.6L Diesel Engine)

The engine oil cooler is a heat exchanger. The engine oil cooler is mounted to the left lower corner of the engine. The oil filter is attached to the oil cooler housing. The engine coolant flows around the oil cooler element. The oil cooler element is a series of plates. The engine oil temperature is regulated by the temperature of the engine coolant that surrounds the oil cooler as the engine oil passes through the cooler.

The engine oil pump, pumps the oil through the engine oil feed line to the oil cooler. The oil then flows down through the cooler while the engine coolant absorbs heat from the oil. The oil is then pumped through the oil return line, to the oil filter, then to the main engine oil passage.

Transmission Oil Cooler

The transmission oil cooler is a heat exchanger. It is located inside the right side end tank of the radiator. The transmission fluid temperature is regulated by the temperature of the engine coolant in the radiator.

The transmission oil pump, pumps the fluid through the transmission oil cooler line to the transmission oil cooler. The fluid then flows through the cooler where the engine coolant absorbs heat from the fluid. The fluid is then pumped through the transmission oil cooler return line, to the transmission.

Turbocharger Bypass Valve (6.6L Diesel Engine)

The turbocharger bypass valve is a temperature control valve. The valve is located in the turbocharger coolant inlet hose at the water outlet tube.

The purpose of the valve is to close the coolant flow through the turbocharger. Closing off the coolant flow through the turbocharger avoids turbocharger overcooling.

Special Tools and Equipment

Special Tools Illustration Tool Number/ Description J 24731 Tempil Stick J 46406 Fan Clutch Remover and Installer J 24460-1 Cooling System Pressure Tester J 41240-5A Fan Clutch Wrench J 42401 Radiator Cap/Surge Tank Test Adapter J 43181 Heater Line Quick Connect Release Tool

Scheme 33

Scheme 34

Scheme 35

Scheme 36

See also:
• SCAN TOOL DOES NOT POWER UP
• SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L
• CHECKING AFTERMARKET ACCESSORIES
• TESTING FOR INTERMITTENT AND POOR CONNECTIONS
• INSTRUMENT PANEL CLUSTER (IPC) REPLACEMENT
• CIRCUIT TESTING
• WIRING REPAIRS
• POWERTRAIN CONTROL MODULE
• CONNECTOR REPAIRS
• FASTENER NOTICE
• ENGINE SIGHT SHIELD REPLACEMENT (4.8L, 5.3L, 6.0L (LQW4))
• LIFTING & JACKING THE VEHICLE
• ENGINE PROTECTION SHIELD REPLACEMENT
• SHIELD REPLACEMENT
• GENERATOR (4.8L, 5.3L & 6.0L ENGINES)
• POWER STEERING PUMP REPLACEMENT (4.8 L, 5.3 L, & 6.0L)
• TRANSMISSION OIL COOLER LINES
• DIAGNOSTIC SYSTEM CHECK - Engine Cooling
• DIAGNOSTIC STARTING POINT - Engine Cooling
• SYMPTOMS - Engine Cooling
• Diagnostic Trouble Code (DTC) List
• Cooling System Connector End Views
• Engine Overheating
• Engine Overheated Indicator Always On
• Engine Coolant Temperature Indicator Always On
• Low Engine Coolant Indicator Always On
• Coolant Heater Inoperative
• Loss of Coolant
• Engine Fails To Reach Normal Operating Temperature
• Fan Clutch Diagnosis
• Pressure Cap Testing
• Fastener Tightening Specifications
• Fan Clutch Replacement
• Fan Replacement