Engine Cooling System Buick Century VI

Fastener Tightening Specifications

Fastener Tightening Specifications

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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 modules which command the system
2. The ability of the control modules 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. 2. 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. 3. Determine if the Instrument Cluster or Powertrain Control Modules have set DTCs which may affect Engine Cooling operation are present.
3. 4. 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.

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Scan Tool Data Definitions

IPC - Inputs - Coolant Hot Lamp: The scan tool displays On or Off. The state of the engine coolant temperature indicator as commanded by the IPC.

PCM - ECT: The scan tool displays -40 to +151°C (-40 to +304°F). The Engine Coolant Temperature (ECT) sensor is mounted in the coolant stream. The PCM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the PCM monitors a high signal voltage and interprets it as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.

PCM - FC Relay 1 Circuit Status: The scan tool displays OK or Fault. This parameter indicates the state of the driver circuit for this device.

PCM - FC Relay 1 Command: The scan tool displays On or Off. This parameter indicates the state of the low speed fan relay driver.

PCM - FC Relay 2 and 3 Circuit Status: The scan tool displays OK or Fault. This parameter indicates the state of the driver circuit for this device.

PCM - FC Relay 2 and 3 Command: The scan tool displays On or Off. This parameter indicates the state of the high speed fan relay driver.

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Circuit Description

The following DTC's are for the cooling fan relay control circuits controlled by the powertrain control module (PCM).

1. P0480 - low speed cooling fan relay control circuit
2. P0481 - high speed cooling fan relay control circuit

Battery positive voltage is supplied to the cool fan 1 relay from the cool fan 1 fuse. The PCM controls the low speed cooling fan relay by grounding the low speed cooling fan relay control circuit.

Battery positive voltage is supplied to the cool fan 2 relay and the cool fan 3 relay from the cool fan 2 fuse. The PCM controls the high speed cooling fan relays by grounding the high speed cooling fan relay control circuit.

The PCM grounds the cooling fan relay control circuits through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the PCM. When the PCM is commanding a component on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM is commanding the control circuit to a component off, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the DTC will set.

The PCM will monitor the control circuit for the following

1. A short to ground
2. A short to voltage
3. An open circuit
4. An open relay coil
5. An internally shorted or excessively low resistance relay coil

When the PCM detects any of the above conditions, the DTC will set and the effected driver will be disabled.

Conditions for Running the DTC

1. The ignition is ON.
2. The system voltage is between 9.0 and 18.0 volts.

Conditions for Setting the DTC

1. An improper voltage level has been detected on the cooling fan relay control circuit.
2. The condition is present for at least 30 seconds.

Action Taken When the DTC Sets

1. The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The PCM will store the conditions that were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC

1. The PCM will turn OFF the MIL during the third consecutive trip in which 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.

Diagnostic Aids

1. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(/buick/century/vi-1997-2005/remont/body-electrical/#wiring-systems__testing-for-intermittent-and-poor-connections) in Wiring Systems.
2. Review the Freeze/Failure Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be occurs.

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

1. 2. Listen for an audible click when the cooling fan 1 relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3. Listen for an audible click when the cooling fan 2 and the cooling fan 3 relays operate. Command both the ON and OFF states. Repeat the commands as necessary.
3. 4. Tests for voltage at the coil side of the cooling fan 1 relay. The cool fan 1 fuse supplies battery positive voltage to the coil side of the cooling fan 1 relay.
4. 5. Verifies that the PCM is providing ground to the cooling fan 1 relay.
5. 6. Tests for voltage at the coil side of the cooling fan 2 relay. The cool fan 2 fuse supplies battery positive voltage to the coil side of the cooling fan 2 and cooling fan 3 relays.
6. 7. Verifies that the PCM is providing ground to the cooling fan 2 relay.
7. 8. Verifies that the PCM is providing ground to the cooling fan 3 relay.
8. 9. Tests if ground is constantly being applied to the cooling fan relays.
9. 10. Test the control circuit of the cooling fan relays for a short to voltage or an open.
10. 11. Test the control circuit of the cooling fan relays for a short to ground.
11. 12. Test the battery positive voltage circuit for a short to ground.

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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»(/buick/century/vi-1997-2005/remont/body-electrical/#wiring-systems__checking-aftermarket-accessories) in Wiring Systems.
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 in Wiring Systems.

Symptom List

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

1. «ENGINE COOLANT TEMPERATURE INDICATOR ALWAYS ON»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)
2. «COOLING FAN ALWAYS ON»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)
3. «COOLING FAN INOPERATIVE»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)
4. «COOLANT HEATER INOPERATIVE»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)
5. «ENGINE OVERHEATING»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)
6. «LOSS OF COOLANT»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)
7. «THERMOSTAT DIAGNOSIS (OVERHEATING)»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) or «THERMOSTAT DIAGNOSIS (SLOW TO HEAT)»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)
8. «ENGINE FAILS TO REACH NORMAL OPERATING TEMPERATURE»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system)

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Pressure Cap Testing

Tools Required

J 24460-01 Cooling System Pressure Tester. See Special Tools and Equipment .

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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. Note the rate of pressure loss.
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. See Special Tools and Equipment .

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1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «PRESSURE CAP TESTING»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system__pressure-cap-testing) .
3. Wash the pressure cap mating surface with water.
4. Use the J 24460-01 in order to apply pressure to the cooling system. Do not exceed the pressure cap rating.
5. The cooling system should hold the rated pressure for at least 2 minutes. Observe the gage for any pressure loss.
6. Repair any leaks as required.

Draining Procedure

1. Park the vehicle on a level surface.
2. Remove the coolant pressure cap.
3. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
4. Place a drain pan under the drain cock.
5. Open the radiator drain cock.
6. Drain the cooling system.
7. If a complete engine block drain is required, remove the engine block drain plug.
8. Inspect the coolant.
9. Follow the appropriate procedure based on the condition of the coolant. Normal in appearance - follow the filling procedure. Discolored - follow the flush procedure. Refer to «FLUSHING»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system__flushing) .

Filling Procedure

Tools Required

J 23688 Coolant and Battery Fluid Tester. See Special Tools and Equipment .

Note. Refer to FASTENER NOTICE in Cautions and Notices.

1. Close the radiator drain cock. Tighten Tighten the radiator drain cock to 2 N.m (18 lb in).
2. If the engine block drain plug was removed, perform the following: 2.1. Apply pipe sealer to the drain plug. 2.2. Install the drain plug. Tighten Tighten the drain plug to 22 N.m (16 lb ft).
3. Lower the vehicle.
4. Open the cooling system bleeder screws. IMPORTANT: Use a 50/50 mixture of DEX-COOL antifreeze and deionized water.
5. Slowly fill the cooling system with a 50/50 coolant mixture.
6. Close the cooling system bleeder screws.
7. Install the coolant pressure cap.
8. Start the engine.
9. Run the engine at 2,000 - 2,500 RPM until the engine reaches normal operating temperature.
10. Allow the engine to idle for 3 minutes.
11. Shut the engine off.
12. Allow the engine to cool.
13. Top off the coolant as necessary.
14. Inspect the concentration of the engine coolant. Using the J 23688 .
15. Rinse away any excess coolant from the engine and the engine compartment.
16. Inspect the cooling system for leaks.

Flushing

Store used coolant in a properly labeled container. Do not pour used coolant down a drain. Ethylene glycol antifreeze is a very toxic chemical. Do not dispose of coolant into the sewer system or ground water. This is illegal and ecologically unsound.

Various methods and equipment can be used to flush the cooling system. If special equipment is used, such as a back flusher, follow the manufacturer's instruction.

When the cooling system becomes contaminated, the cooling system should be flushed thoroughly to remove the contaminants before the engine is seriously damaged.

1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the coolant recovery reservoir. Refer to «COOLANT RECOVERY RESERVOIR REPLACEMENT»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Clean and flush the coolant recovery reservoir with clean, drinkable water.
4. Install the coolant recovery reservoir. Refer to «COOLANT RECOVERY RESERVOIR REPLACEMENT»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Follow the drain and fill procedure using only clean, drinkable water. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
6. Run the engine for 20 minutes.
7. Stop the engine.
8. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
9. Repeat the procedure if necessary, until the fluid is nearly colorless.
10. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

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.

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1. Reposition the coolant reservoir hose clamp (1) at the radiator overflow fitting.
2. Remove the coolant reservoir hose from the radiator overflow fitting.
3. Remove the nuts (2) from the shock tower studs.
4. Remove the coolant recovery reservoir (3) from the lower retainer and the shock tower studs.
5. Drain the coolant from the recovery reservoir in to a clean container.

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1. Install the coolant recovery reservoir (3) to the lower retainer and the shock tower studs. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the nuts (2) to the shock tower studs. Tighten Tighten the nuts to 3.3 N.m (29 lb in).
3. Lubricate the reservoir hose with clean water. Route the hose to the radiator overflow neck fitting.
4. Install the coolant reservoir hose (1), to the radiator overflow fitting. IMPORTANT: The hose end must be flush against the radiator filler neck. Seat the clamp squarely between the radiator filler neck and the flared end of the fitting.
5. Reposition the coolant reservoir hose clamp to the radiator overflow fitting.
6. Fill the coolant recovery reservoir to the proper level.

Radiator Hose Replacement - Inlet (3.1L)

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

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1. Partially drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the left diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
3. Use the J 38185 in order to reposition the hose clamp at the thermostat housing.
4. Disconnect the radiator inlet hose from the thermostat housing.
5. Use the J 38185 in order to reposition the hose clamp at the radiator.
6. Disconnect the radiator inlet hose from the radiator.
7. Remove the radiator inlet hose.

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1. Position the radiator inlet hose to the vehicle. Align the marks on the hose.
2. Install the radiator inlet hose to the radiator.
3. Use the J 38185 in order to reposition and install the hose clamp at the radiator.
4. Install the radiator inlet hose to the thermostat housing.
5. Use the J 38185 in order to reposition and install the hose clamp at the thermostat housing.
6. Install the left diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
7. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Radiator Hose Replacement - Inlet (3.8L)

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

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1. Partially drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the left diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
3. Use the J 38185 in order to reposition the hose clamp at the radiator.
4. Disconnect the radiator inlet hose from the radiator.
5. Use the J 38185 in order to reposition the hose clamp at the thermostat housing.
6. Disconnect the radiator inlet hose from the thermostat housing.
7. Remove the radiator inlet hose.

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1. Install the radiator inlet hose into position and align the marks on the hose.
2. Install the radiator inlet hose to the thermostat housing.
3. Use the J 38185 in order to reposition and install the hose clamp at the thermostat housing.
4. Install the radiator inlet hose to the radiator.
5. Use the J 38185 in order to reposition and install the hose clamp at the radiator.
6. Install the left diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
7. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Radiator Hose Replacement - Outlet (3.1L)

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

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1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Use the J 38185 in order to reposition the hose clamp from the water pump housing.
3. Disconnect the outlet hose (3) from the water pump housing (1).
4. Remove the lower radiator air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Use the J 38185 in order to reposition the hose clamp from the radiator.
6. Disconnect the outlet hose (3) from the radiator (2).
7. Remove the outlet hose.

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1. Align the marks on the radiator hose. Install the outlet hose to the radiator.
2. Install the outlet hose (3) to the radiator (2).
3. Use the J 38185 in order to reposition the hose clamp to the radiator.
4. Install the lower radiator air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Install the outlet hose (3) to the water pump housing (1).
6. Use the J 38185 in order to reposition the hose clamp to the water pump housing
7. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Radiator Hose Replacement - Outlet (3.8L)

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

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1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the lower radiator air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Use the J 38185 in order to reposition the hose clamp from the radiator.
4. Disconnect the outlet hose from the radiator.
5. Lower the vehicle.
6. Use the J 38185 in order to reposition the hose clamp from the water pump housing.
7. Disconnect the outlet hose from the water pump housing.
8. Remove the outlet hose.

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1. Align the marks on the hose. Install the outlet hose to the water pump housing.
2. Use the J 38185 in order to reposition the hose clamp to the water pump housing.
3. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
4. Install the outlet hose to the radiator.
5. Use the J 38185 in order to reposition the outlet hose to the radiator.
6. Install the lower radiator air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
7. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

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1. Remove the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.
2. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the throttle body inlet hose clamp and the hose (3) from the coolant pipe.
4. Remove the throttle body inlet hose clamp and the hose from the throttle body.
5. Remove the throttle body inlet hose (3).

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1. Install the throttle body inlet hose (3).
2. Install the throttle body inlet hose and the clamp to the throttle body.
3. Install the throttle body inlet hose (3) and the clamp to the coolant pipe.
4. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Install the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.

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1. Remove the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.
2. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the throttle body outlet hose clamp and the hose (4) from the coolant pipe.
4. Remove the throttle body outlet hose clamp and the hose from the throttle body.
5. Remove the throttle body outlet hose (4).

Scheme 51

1. Install the throttle body outlet hose (4).
2. Install the throttle body outlet hose and the clamp to the throttle body.
3. Install the throttle body outlet hose (4) and the clamp to the coolant pipe.
4. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
5. Install the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.

Removal Procedure

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1. Disconnect the negative battery cable. Refer to BATTERY NEGATIVE CABLE DISCONNECT/CONNECT PROCEDURE in Battery.
2. Disconnect the cooling fan electrical connector.
3. Partially drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Remove the LH and RH engine mount strut braces. Refer to ENGINE MOUNT STRUT REPLACEMENT in Engine Mechanical - 3.1L or ENGINE MOUNT STRUT REPLACEMENT - RIGHT and ENGINE MOUNT STRUT REPLACEMENT - LEFT in Engine Mechanical -3.8L.
5. Remove the left front fender upper diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
6. Remove the air cleaner and duct assembly.
7. Remove the radiator inlet hose from the radiator.
8. Remove the PCM harness from the fan shroud clip.
9. Remove the cooling fan shroud bolts.
10. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
11. Remove the push pin retainer from the lower left side of the fan shroud.
12. Remove the transmission oil cooler lines from the retainer clip at the bottom of the cooling fan shroud.
13. Lower the vehicle.
14. Remove the cooling fan shroud clip from the top of the radiator.
15. Remove the radiator upper support brackets that connect to the fan shroud.
16. Remove the fan motor heat shields.
17. Remove the cooling fan shroud.

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1. Install the cooling fan shroud.
2. Install the cooling fan shroud clip to the top of the radiator. Apply pressure in order to completely engage the clip onto the radiator. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the cooling fan shroud bolts. Tighten Tighten the bolts to 6 N.m (53 lb in).
4. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
5. Install the push pin retainer to the lower left side of the fan shroud.
6. Install the transmission oil cooler lines on to the retainer at the bottom of the cooling fan shroud.
7. Lower the vehicle.
8. Install the fan motor heat shields.
9. Install the radiator upper support brackets and bolts that hold the fan shroud. Tighten Tighten the bolts to 10 N.m (89 lb in).
10. Connect the cooling fan electrical connector.
11. Install the radiator inlet hose to the radiator.
12. Install the air cleaner and duct assembly. Refer to
13. Install the left front fender upper diagonal brace. Refer to BRACE REPLACEMENT - FRONT FENDER UPPER DIAGONAL in Body Front End.
14. Install the PCM harness on to the fan shroud clip.
15. Install the LH and RH engine mount strut braces. Refer to ENGINE MOUNT STRUT REPLACEMENT in Engine Mechanical - 3.1L or ENGINE MOUNT STRUT REPLACEMENT - RIGHT and ENGINE MOUNT STRUT REPLACEMENT - LEFT in Engine Mechanical -3.8L.
16. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
17. Connect the negative battery cable. Refer to BATTERY NEGATIVE CABLE DISCONNECT/CONNECT PROCEDURE in Battery.

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1. Remove the cooling fan assembly. Refer to «COOLING FAN REPLACEMENT - ELECTRIC»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Disconnect the cooling fan motors electrical connectors.
3. Remove the cooling fan blade nut.
4. Remove the cooling fan blade. CAUTION: If a fan blade is bent or damaged in any way, do not repair or reuse the damaged part. Always replace a bent or damaged fan blade. Fan blades that have been damaged can not be assured of proper balance and could fail and fly apart during subsequent use. This creates an extremely dangerous situation. The fan blades must remain in proper balance. You cannot assure fan blade balance once a fan blade has been bent or damaged. A fan blade that is not in proper balance could fail and fly apart during use, creating an extremely dangerous situation.
5. Inspect the cooling fan for the following conditions: Bent or cracked cooling fan blades Smoothness of the cooling fan blade mating surfaces Remove burrs or other imperfections as necessary
6. Remove the cooling fan motor bolts.
7. Remove the cooling fan motor.

Scheme 60

Scheme 61

1. Install the cooling fan motor. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the cooling fan motor bolts. Tighten Tighten the bolts to 6 N.m (53 lb in).
3. Install the cooling fan blade.
4. Install the cooling fan blade nut. Tighten Tighten the nut to 6 N.m (53 lb in).
5. Connect the cooling fan motors electrical connectors.
6. Install the cooling fan assembly. Refer to «COOLING FAN REPLACEMENT - ELECTRIC»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Thermostat Replacement (3.1L)

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

Scheme 62

Scheme 63

Scheme 64

1. Remove the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.
2. Partially drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Use the J 38185 in order to reposition the hose clamp from the water outlet housing.
4. Remove the radiator inlet hose from the water outlet housing.
5. Remove the exhaust crossover pipe. Refer to EXHAUST CROSSOVER PIPE REPLACEMENT (3.1L) or EXHAUST CROSSOVER PIPE REPLACEMENT (3.8L) in Engine Exhaust.
6. Remove the water outlet housing bolts.
7. Remove the water outlet housing and the gasket.
8. Remove the thermostat.
9. Clean and inspect the water outlet housing gasket mating surfaces.

Scheme 65

Scheme 66

Scheme 67

1. Install the thermostat.
2. Install the water outlet gasket and the water outlet housing. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the water outlet housing bolts. Tighten Tighten the bolts to 25 N.m (18 lb ft).
4. Install the exhaust crossover pipe. Refer to EXHAUST CROSSOVER PIPE REPLACEMENT (3.1L) or EXHAUST CROSSOVER PIPE REPLACEMENT (3.8L) in Engine Exhaust.
5. Install the radiator inlet hose to the water outlet housing.
6. Use the J 38185 in order to reposition and install the hose clamp to the water outlet housing.
7. Install the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.
8. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Thermostat Replacement (3.8L)

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

Scheme 68

Scheme 69

1. Remove the fuel injector sight shield. Refer to FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L36) or FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L67) in Engine Mechanical - 3.8L.
2. Partially drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Use the J 38185 in order to reposition the hose clamp from the water outlet housing.
4. Remove the radiator inlet hose from the water outlet housing.
5. Remove the water outlet housing bolt and the stud. Remove the water outlet housing and the gasket.
6. Remove the thermostat.
7. Clean and Inspect the water outlet housing gasket mating surfaces.

Scheme 70

Scheme 71

1. Install the thermostat.
2. Install the gasket and the water outlet housing. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the water outlet housing bolt and the stud to the water outlet housing. Tighten Tighten the bolt and the stud to 27 N.m (20 lb ft).
4. Install the radiator inlet hose to the water outlet housing.
5. Use the J 38185 in order to reposition and install the hose clamp to the water outlet housing.
6. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
7. Install the fuel injector sight shield. Refer to FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L36) or FUEL INJECTOR SIGHT SHIELD REPLACEMENT (L67) in Engine Mechanical - 3.8L.

Thermostat Bypass Pipes Replacement

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

Scheme 72

Scheme 73

Scheme 74

Scheme 75

Scheme 76

1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) in Engine Cooling.
2. Remove the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.
3. Remove the LH engine mount strut. Refer to ENGINE MOUNT STRUT REPLACEMENT in Engine Mechanical - 3.1L.
4. Remove the spark plug wires from the left bank.
5. Use the J 38185 in order to reposition the hose clamp from the water outlet housing.
6. Remove the upper radiator inlet hose from the water outlet housing.
7. Remove the heater outlet hose (2) from the thermostat bypass pipe.
8. Remove the throttle body inlet and outlet hoses (1) from the thermostat bypass pipe.
9. Remove the thermostat bypass pipe nut.
10. Use the J 38185 to reposition the hose clamp from the thermostat bypass pipe.
11. Remove the thermostat bypass pipe hose from the pipe.
12. Remove the thermostat bypass pipe bolt.
13. Remove the thermostat bypass pipe.

Scheme 77

Scheme 78

Scheme 79

Scheme 80

Scheme 81

1. Install the thermostat bypass pipe. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the thermostat bypass pipe bolt. Tighten Tighten the bolt to 11 N.m (98 lb in).
3. Install the thermostat bypass hose to the pipe.
4. Use the J 38185 to reposition and install the hose clamp to the thermostat bypass pipe.
5. Install the thermostat bypass pipe nut. Tighten Tighten the nut to 25 N.m (18 lb ft).
6. Install the heater outlet hose (2) to the thermostat bypass pipe.
7. Install the throttle body inlet and outlet hoses (1) to the thermostat bypass pipe.
8. Install the radiator inlet hose to the water outlet housing.
9. Use the J 38185 to reposition and install the hose clamp to the water outlet housing.
10. Install the spark plug wires to the left bank.
11. Install the LH engine mount strut. Refer to ENGINE MOUNT STRUT REPLACEMENT in Engine Mechanical - 3.1L.
12. Install the air cleaner intake duct. Refer to «AIR CLEANER INTAKE DUCT»(/buick/century/vi-1997-2005/remont/automatic-trans/#automatic-transaxle-removal-installation) in Removal & Installation - A/T.
13. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) in Engine Cooling.

Scheme 82

Scheme 83

1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the drive belt shield bolt and the shield.
3. Loosen the water pump pulley bolts.
4. Remove the drive belt. Refer to DRIVE BELT REPLACEMENT in Engine Mechanical - 3.1L.
5. Remove the water pump pulley bolts.
6. Remove the water pump pulley.
7. Remove the water pump bolts.
8. Remove the water pump.
9. Remove the water pump gasket.
10. Clean the water pump mating surfaces.

Scheme 84

Scheme 85

1. Install the gasket.
2. Install the water pump. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the water pump bolts. Tighten Tighten the bolts to 10 N.m (89 lb in).
4. Install the water pump pulley.
5. Install the water pump pulley bolts. Tighten Tighten the bolts to 25 N.m (18 lb ft).
6. Install the drive belt. Refer to DRIVE BELT REPLACEMENT in Engine Mechanical - 3.1L.
7. Install the drive belt shield and the bolt. Tighten Tighten the bolt to 10 N.m (89 lb in).
8. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Scheme 86

Scheme 87

Scheme 88

1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Reposition the accessory wiring junction block.
3. Loosen the water pump pulley bolts.
4. Remove the drive belt. Refer to DRIVE BELT REPLACEMENT (L36) or DRIVE BELT REPLACEMENT (L67) in Engine Mechanical-3.8L.
5. Remove the water pump pulley bolts.
6. Remove the water pump pulley.
7. Remove the power steering pump mounting bolts and reposition. Refer to POWER STEERING PUMP REPLACEMENT (3.8L) or POWER STEERING PUMP REPLACEMENT (3.1L) in Power Steering System.
8. Remove the water pump bolts.
9. Remove the water pump.
10. Remove the water pump gasket.
11. Clean and inspect the water pump gasket mating surfaces.

Scheme 89

Scheme 90

1. Install the gasket and the water pump. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the water pump bolts. Tighten Tighten the long water pump bolts to 34 N.m (25 lb ft). Tighten the short water pump bolts to 22 N.m (16 lb ft).
3. Install the water pump pulley.
4. Install the water pump pulley bolts. Tighten Tighten the bolts to 13 N.m (115 lb in).
5. Install the power steering pump. Refer to POWER STEERING PUMP REPLACEMENT (3.8L) or POWER STEERING PUMP REPLACEMENT (3.1L) in Power Steering System.
6. Install the drive belt. Refer to DRIVE BELT REPLACEMENT (L36) or DRIVE BELT REPLACEMENT (L67) in Engine Mechanical-3.8L.
7. Install the accessory wiring junction block.
8. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Scheme 91

1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Remove the lower air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the radiator drain plug and seal. The seal usually comes out attached to the plug.
4. Remove the body of the drain plug. Use your fingers or needlenose pliers to disengage the locking tabs from the side tank.
5. Clean the drain cock and the drain cock plug.

Scheme 92

1. Install the seal on the drain cock plug stem.
2. Install the drain cock plug. Make sure that the body is fully seated in the side tank and that the locking tabs are engaged.
3. Install the lower air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Scheme 93

Scheme 94

1. Remove the cooling fans. Refer to «COOLING FAN REPLACEMENT - ELECTRIC»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Disconnect the cooling fan wiring harness from each cooling fan motor.
3. Remove the cooling fan electrical harness from the fan shroud.
4. Remove the cooling fan blade nuts.
5. Remove the cooling fan blades.
6. Remove the cooling fan motors bolts.
7. Remove the cooling fan motors from the fan shroud.

Scheme 95

Scheme 96

1. Install the cooling fan motors onto the fan shroud. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the cooling fan motors bolts. Tighten Tighten the bolts to 6 N.m (53 lb in). CAUTION: If a fan blade is bent or damaged in any way, do not repair or reuse the damaged part. Always replace a bent or damaged fan blade. Fan blades that have been damaged can not be assured of proper balance and could fail and fly apart during subsequent use. This creates an extremely dangerous situation. The fan blades must remain in proper balance. You cannot assure fan blade balance once a fan blade has been bent or damaged. A fan blade that is not in proper balance could fail and fly apart during use, creating an extremely dangerous situation.
3. Install the cooling fan blades.
4. Install the cooling fan blade nuts. Tighten Tighten the nuts to 6 N.m (53 lb in).
5. Install the cooling fan electrical harness to the fan shroud.
6. Connect the cooling fan wiring harness to each cooling fan motor.
7. Install the cooling fans. Refer to «COOLING FAN REPLACEMENT - ELECTRIC»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Radiator Replacement

Tools Required

J 38185 Hose Clamp Pliers. See Special Tools and Equipment .

Scheme 97

Scheme 98

Scheme 99

Scheme 100

Scheme 101

Scheme 102

1. Remove the battery. Refer to BATTERY REPLACEMENT in Battery.
2. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
3. Remove the cooling fan assembly. Refer to «COOLING FAN REPLACEMENT - ELECTRIC»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
4. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
5. Remove the lower air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
6. Use J 38185 to remove the outlet hose clamp from the radiator.
7. Remove the outlet hose from the radiator.
8. Lower the vehicle.
9. Disconnect the transaxle oil cooler pipes from the radiator.
10. Pull the plastic cap back from the quick connect fitting and down along the transaxle oil cooler pipe.
11. Using a bent-tip screwdriver, pull on one of the open ends of the retaining ring in order to rotate the retaining ring around the quick connect fitting until the retaining ring is out of position and can be completely removed.
12. Remove the retaining ring from the quick connect fitting.
13. Discard the retaining ring.
14. Pull the transaxle oil cooler pipe straight out from the quick connect fitting.
15. Remove the radiator.

Scheme 103

Scheme 104

Scheme 105

Scheme 106

Scheme 107

Scheme 108

Scheme 109

Scheme 110

Scheme 111

Scheme 112

Scheme 113

Scheme 114

Scheme 115

1. Install the radiator to the lower mounts.
2. Install the transaxle oil cooler pipes. IMPORTANT: Install new retaining rings into the quick connect fittings.
3. Ensure the following procedures are performed when installing the new retaining ring onto the fitting.
4. Hook one of the open ends of the retaining ring in one of the slots in the quick connect fitting.
5. Rotate the retaining ring around the fitting until the retaining ring is positioned with all three ears through the three slots on the fitting. IMPORTANT: DO NOT Push the new retaining ring onto the fitting.
6. Installing the retaining ring on to the fitting this way will bend the retaining ring.
7. Ensure that the three retaining ring ears are seen from inside the fitting and that the retaining ring moves freely in the fitting slots.
8. Install the transaxle oil cooler pipes into the radiator quick connect fitting.
9. Insert the transaxle oil cooler pipe ends into the quick connect fitting until you hear or feel a click.
10. Do not use the plastic cap on the transaxle oil cooler pipe in order to install the transaxle oil cooler pipe into the fitting.
11. Pull back sharply on the transaxle oil cooler pipe in order to ensure that the transaxle oil cooler pipe is fastened into the quick connect fitting.
12. Position the plastic cap onto the fitting. Do not manually depress the retaining ring when installing the plastic cap onto the quick connect fitting.
13. Fully seat the plastic cap against the fitting.
14. Allow no gap between the cap and the fitting.
15. Ensure that the yellow identification band on the tube is hidden within the quick connect fitting. A hidden yellow identification band indicates proper joint seating. NOTE: Do NOT overfill the transaxle. The overfilling of the transaxle causes foaming, loss of fluid, shift complaints, and possible damage to the transaxle.
16. Adjust the fluid level.
17. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
18. Install the outlet hose to the radiator.
19. Use J 38185 to install the outlet hose clamp to the radiator.
20. Install the lower air deflector. Refer to «RADIATOR AIR BAFFLE AND DEFLECTOR REPLACEMENT - LOWER»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
21. Lower the vehicle.
22. Install the cooling fan assembly. Refer to «COOLING FAN REPLACEMENT - ELECTRIC»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
23. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
24. Install the battery. Refer to BATTERY REPLACEMENT in Battery.

Scheme 116

1. Raise and suitably support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
2. Remove the radiator lower air deflector bolts.
3. Remove the radiator lower air deflector.

Scheme 117

1. Install the radiator lower air deflector. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the radiator lower air deflector bolts. Tighten Tighten the bolts to 20 N.m (15 lb ft).
3. Lower the vehicle.

Scheme 118

1. Remove the right and left side air baffle push-in retainers.
2. Remove the right and left side air baffles.

Scheme 119

1. Install the right and left side air baffles to the vehicle.
2. Install the right and left side air baffle push-in retainers.

Scheme 120

1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
3. Disconnect the engine coolant heater cord from the engine coolant heater.
4. Loosen the engine coolant heater bolt. Do not remove the engine coolant heater bolt.
5. Remove the engine coolant heater.
6. Clean the engine coolant heater opening.

Scheme 121

1. Apply GM P/N 12346004, (Canadian P/N 10953480) or the equivalent to the following: The engine block heater seal The cleaned surface of the engine block heater hole
2. Position the engine coolant heater element at the 3 o'clock position (2).
3. Install the engine coolant heater. Final installed position between 2 o'clock (1) and 4 o'clock (3) is acceptable. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Install the engine coolant heater bolt. Tighten Tighten the bolt to 2 N.m (18 lb in).
5. Connect the engine coolant heater cord to the engine coolant heater.
6. Lower the vehicle.
7. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Scheme 122

1. Drain the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .
2. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
3. Disconnect the coolant heater cord from the coolant heater.
4. Loosen the bolt at the coolant heater but DO NOT remove the coolant heater bolt.
5. Remove the coolant heater.
6. Remove and clean any burrs, compound, paint, or rough spots from the core plug hole.

Scheme 123

Scheme 124

1. Apply GM P/N 12346004, (Canadian P/N 10953480) or equivalent to the following: Engine block heater seal Cleaned surface of the engine block heater hole
2. Install the coolant heater by pushing tight to the block.
3. Position the engine coolant heater element at the 9 o'clock position (2). Final installed position between 10 o'clock (1) and 8 o'clock (3) is acceptable. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Tighten the coolant heater bolt until both locking wings draw tight against the inner wall of the engine block. Tighten Tighten the bolt to 2 N.m (17 lb in).
5. Connect the engine coolant heater cord to the engine coolant heater.
6. Fill the cooling system. Refer to «DRAINING AND FILLING COOLING SYSTEM»(/buick/century/vi-1997-2005/remont/cooling-system-mechanical/#engine-cooling-system) .

Scheme 125

1. Raise and support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/buick/century/vi-1997-2005/remont/hoistjack/#jacking-and-lifting__lifting-and-jacking-the-vehicle) in General Information.
2. Disconnect the engine block heater cord from the engine block heater.
3. Remove the engine block heater cord straps.
4. Disconnect the upper engine block heater cord from the diagonal brace strap.
5. Remove the engine block heater cord.

Installation Procedure

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.

Scheme 126

1. Install the engine block heater cord.
2. Connect the engine block heater cord to the diagonal brace strap.
3. Install the new engine block heater cord straps.
4. Connect the engine block heater cord to the engine block heater.
5. Lower the vehicle.

Scheme 127

1. Remove the coolant heater cord retainer from the upper radiator support.
2. Cut the coolant heater cord straps at the engine wiring harness.
3. Disconnect the coolant heater cord from the coolant heater.
4. Remove the coolant heater cord from the vehicle.

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.

Scheme 128

1. Install the coolant heater cord to the vehicle.
2. Connect the coolant heater cord to the coolant heater.
3. Install a new coolant heater cord straps at the engine wiring harness.
4. Install the coolant heater cord retainer to the upper radiator support.

Cooling Fan Control 3.1 L (LG8)

The engine cooling fan system consists of two electrical cooling fans and three 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 accessory wiring junction block. The ground path is provided at G117.

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 cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage from the cool fan 1 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 2 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 cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan 3 relay through the high speed cooling fan relay control circuit. This energizes the cooling fan 2 relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the cooling fan 3 relay coil is energized closing the relay contacts and provides battery positive voltage from the cool fan 2 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.

A diode is in parallel with each of the cooling fan motors. This diode absorbs a voltage surge and protects the vehicles electrical system. This surge results from the initial start-up of the cooling fan motor.

The PCM commands Low Speed Fans on under the following conditions

1. Engine coolant temperature exceeds approximately 106°C (223°F).
2. When A/C is requested and the ambient temperature is more than 50°C (122°F).
3. A/C refrigerant pressure exceeds 1310 kPa (190 psi).
4. After the vehicle is shut off if the engine coolant temperature at key-off is more than 140°C (284°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The PCM commands High Speed Fans on under the following conditions

1. Engine coolant temperature reaches 110°C (230°F).
2. A/C refrigerant pressure exceeds 1655 kPa (240 psi).
3. When certain DTCs set.

Cooling Fan Control 3.8L (L36, L67)

The engine cooling fan system consists of two electrical cooling fans and three 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 accessory wiring junction block. The ground path is provided at G117.

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 cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage from the cool fan 1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the cooling fan 2 relay and the left 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 cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan 3 relay through the high speed cooling fan relay control circuit. This energizes the cooling fan 2 relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time the cooling fan 3 relay coil is energized closing the relay contacts and provides battery positive voltage from the cool fan 2 fuse on the cooling fan motor supply voltage circuit to the left 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 Low Speed Fans on under the following conditions

1. Engine coolant temperature exceeds approximately 106°C (223°F).
2. When A/C is requested and the ambient temperature is more than 50°C (122°F).
3. A/C refrigerant pressure exceeds 1310 kPa (190 psi).
4. After the vehicle is shut off if the engine coolant temperature at key-off is more than 140°C (284°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The PCM commands High Speed Fans on under the following conditions

1. Engine coolant temperature reaches 110°C (230°F).
2. A/C refrigerant pressure exceeds 1655 kPa (240 psi).
3. When certain DTCs set.

TEMP

1. The IPC illuminates the TEMP indicator when the PCM determines that the coolant temperature is more than 128°C (262°F). The IPC receives a discrete input from the PCM requesting illumination.
2. The IPC performs the displays test at the start of each ignition cycle. The IPC illuminates the TEMP indicator.

Coolant Heater

The optional engine coolant heater (RPO K05) operates using 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 system cools slowly or not at all. 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. Some coolant will then be pumped from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost.

Coolant is also pumped 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.

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 keeping the throttle body cool.

From the cylinder heads, the coolant is then forced to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine is warmed, or it will flow through the thermostat and into the radiator where it is cooled and the coolant cycle is completed.

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 clean drinkable 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 crossflow tube and fin design. This is a series of tubes that extend side to side from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer from the coolant to the atmosphere. The inlet and outlet tanks are molded with a high temperature, nylon reinforced plastic. A high temperature rubber gasket seals the tank flange edge. 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 which is located in the bottom of the left hand tank. The drain cock includes the drain cock and drain cock seal.

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

During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.

Pressure Cap

The pressure cap is a cap that seals and pressurizes the cooling system. It contains a blow off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring of predetermined strength, which protects the radiator by relieving pressure if it exceeds 15 psi. 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 to collapse.

The pressure cap allows pressure in the cooling system to build up. As the pressure builds, the boiling point of the coolant goes up as well. Therefore, the 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 moves from the radiator to the cooler, passing air. The pressure in the cooling system can get too high, however. When the pressure exceeds the strength of the spring, it raises the pressure valve so that the excess pressure can escape. 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 cooling system. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator from collapsing.

Coolant Recovery System

The coolant recovery system consists of a plastic coolant recovery reservoir and overflow tube. The recovery reservoir is also called a recovery tank or expansion tank. It is partially filled with coolant and is connected to the radiator fill neck with the overflow tube. Coolant can flow back and forth between the radiator and the reservoir.

In effect, a cooling system with a coolant recovery reservoir is a closed system. When the pressure in the cooling system gets too high, it will open the pressure valve in the pressure cap. This allows the coolant, which has expanded due to being heated, is allowed to flow through the overflow tube and into the recovery reservoir. As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum opens the vacuum valve in the pressure cap, allowing some of the coolant in the reservoir to be siphoned back into the radiator. Under normal operating conditions, no coolant is lost. Although the coolant level in the recovery reservoir goes up and down, the radiator and cooling system are kept full. An advantage to using a coolant recovery reservoir is that it eliminates almost all air bubbles from the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.

Air Baffles and Seals

The cooling system uses deflectors, air baffles and air seals to increase system cooling. Deflectors are installed under the vehicle to redirect airflow beneath the vehicle to flow through the radiator and increase cooling. Air baffles are also used to direct airflow into the radiator and increase cooling. Air seals prevent air from bypassing the radiator and A/C condenser. Air seals also prevent recirculation of the 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 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 one or more sealed bearings. These sealed bearings never need to be lubricated. With a sealed bearing, grease cannot leak out, and dirt and water cannot get in.

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.

Thermostat

The thermostat is a coolant flow control component. It's purpose is to regulate the operating temperature of the engine. It 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 diaphragm. 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 91 °C (195°F), the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 91 °C (195°F), 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, even 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.

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.

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 that surrounds the oil cooler as the transmission fluid passes down through the cooler.

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

Scheme 129

Scheme 130

See also:
• TESTING FOR INTERMITTENT AND POOR CONNECTIONS
• CHECKING AFTERMARKET ACCESSORIES
• LIFTING AND JACKING THE VEHICLE
• FASTENER NOTICE
• AIR CLEANER INTAKE DUCT
• DIAGNOSTIC SYSTEM CHECK - ENGINE COOLING
• PRESSURE CAP TESTING
• FLUSHING