Engine Cooling System: Other GMC Terrain I

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «COMPONENT CONNECTOR END VIEWS - INDEX»(ref-493129-S29400264122012080800000)
2. «Electrical Center Identification Views»(ref-491213-S19440762712012073000000)

Description and Operation

Cooling Fan Description and Operation (3.0L) , Cooling Fan Description and Operation (2.4L)

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-491170-S23088445062012073000000)
4. «Wiring Repairs»(ref-491170-S24000289392012073000000)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Engine operating, command the cooling fans ON and OFF at high speed. Verify both fans operate as commanded.
2. Engine operating, observe the DTC information with a scan tool. DTC P0480, P0481, P0691, P0692, P0693, or P0694 should not set.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(ref-491162-S05710312252012073000000) , «Relay Replacement (Attached to Wire Harness)»(ref-491162-S38963856272012073000000)
2. «Control Module References»(ref-491163-S28884786072012073000000) for ECM replacement, setup, and programming

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «COMPONENT CONNECTOR END VIEWS - INDEX»(ref-493129-S29400264122012080800000)
2. «Electrical Center Identification Views»(ref-491213-S19440762712012073000000)

Description and Operation

Cooling Fan Description and Operation (3.0L) , Cooling Fan Description and Operation (2.4L)

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-491170-S23088445062012073000000)
4. «Wiring Repairs»(ref-491170-S24000289392012073000000)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, command the appropriate Cooling Fan Relay ON and OFF with a scan tool. You should hear the relay click when commanded ON and OFF.
2. Engine operating, observe the DTC information with a scan tool. DTC P0480, P0481, P0691, P0692, P0693, or P0694 should not set.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(ref-491162-S05710312252012073000000) , «Relay Replacement (Attached to Wire Harness)»(ref-491162-S38963856272012073000000)
2. «Control Module References»(ref-491163-S28884786072012073000000) for ECM replacement, setup, and programming

Schematic Reference

Engine Controls Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Cooling Fan Description and Operation (3.0L)»(ref-491221-S17614761102012073000000) , «Cooling Fan Description and Operation (2.4L)»(ref-491221-S03062725782012073000000)
2. «Instrument Cluster Description and Operation»(ref-491159-S38460012292012073000000)
3. «Indicator/Warning Message Description and Operation»(ref-491159-S06972001192012073000000)

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Wiring Repairs»(ref-491170-S24000289392012073000000)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Engine Control Module Scan Tool Information (LFX or LFW) , Engine Control Module Scan Tool Information (LEA) for scan tool information

Note. If DTC P0480, P0481, P0691, P0692, P0693, or P0694 is set, diagnose that DTC first.

1. Observe the engine coolant level. The engine coolant level should be within the operating range. Refer to «Cooling System Draining and Filling (GE 47716)»(ref-491221-S11227726582012073000000) , «Cooling System Draining and Filling (Static LF1 or LFW)»(ref-491221-S01432179932012073000000) , «Cooling System Draining and Filling (Static LAF or LEA)»(ref-491221-S24420276232012073000000) .
2. Ensure that the vehicle has the correct engine coolant with correct concentration and is not old, contaminated, or contains additives. Refer to «Cooling System Draining and Filling (GE 47716)»(ref-491221-S11227726582012073000000) , «Cooling System Draining and Filling (Static LF1 or LFW)»(ref-491221-S01432179932012073000000) , «Cooling System Draining and Filling (Static LAF or LEA)»(ref-491221-S24420276232012073000000) .
3. Inspect the cooling system for the following: Leaks Kinked or pinched hoses, especially at the radiator Loose, missing, or damaged radiator air seals or deflectors Air flow obstructions or bent fins at the radiator or the A/C condenser-Refer to «Symptoms - Engine Cooling»(ref-491221-S32934727172012073000000) .
4. Command the cooling fans ON and OFF, low and high speed. The engine cooling fans should turn ON and OFF with each command. If the cooling fans do not function as indicated, refer to «Cooling Fan Inoperative (LEA)»(ref-491221-S32168532422012073000000) , «Cooling Fan Inoperative (LFW)»(ref-491221-S13580085482012073000000) .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Identifying Intermittent Conditions

Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movement of a component. Refer to the following for a list to help isolate an intermittent condition

1. Water intrusion in connectors, terminals, or components
2. Poor connector mating
3. Terminal contact
4. High circuit or component resistance-High resistance can include any resistance, regardless of the amount, which can interrupt the operation of the component.
5. Harness' that are routed too tight, or chaffed circuits
6. High or low ambient temperatures
7. High or low engine coolant temperatures
8. High underhood temperatures
9. Heat build up in components or circuits due to circuit resistance, poor terminal contact, or high electrical load
10. High or low system voltage
11. High vehicle load conditions
12. Rough road surface
13. Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge
14. Incorrect installation of non-factory, aftermarket, or after factory add on accessories

If an intermittent is detected, refer to Testing for Intermittent Conditions and Poor Connections for specific strategies in diagnosing intermittent conditions.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «COMPONENT CONNECTOR END VIEWS - INDEX»(ref-493129-S29400264122012080800000)
2. «Electrical Center Identification Views»(ref-491213-S19440762712012073000000)

Description and Operation

Cooling Fan Description and Operation (3.0L) , Cooling Fan Description and Operation (2.4L)

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-491170-S23088445062012073000000)
4. «Wiring Repairs»(ref-491170-S24000289392012073000000)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480, P0481, P0691, P0692, P0693, or P0694 should not set. If a DTC is set, refer to «DTC P0480, P0481, P0691, P0692, P0693, or P0694 (LFW)»(ref-491221-S21396474462012073000000) , «DTC P0480, P0481, P0691, P0692, P0693, or P0694 (LEA)»(ref-491221-S17712502082012073000000) .
2. Ignition ON, observe the scan tool parameters listed below. Verify that both parameters display OFF. Cooling Fan Relay 1 Command Cooling Fan Relays 2 Command
3. Ignition ON, observe that the fan is not activated.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement (Within an Electrical Center) , Relay Replacement (Attached to Wire Harness)

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «COMPONENT CONNECTOR END VIEWS - INDEX»(ref-493129-S29400264122012080800000)
2. «Electrical Center Identification Views»(ref-491213-S19440762712012073000000)

Description and Operation

Cooling Fan Description and Operation (3.0L) , Cooling Fan Description and Operation (2.4L)

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-491170-S23088445062012073000000)
4. «Wiring Repairs»(ref-491170-S24000289392012073000000)

Scan Tool Reference

Control Module References for scan tool information

1. ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480, P0481, P0691, P0692, P0693, or P0694 is not set. If a DTC is set, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(ref-491140-S28645929192012073000000) .
2. Ignition ON, observe the scan tool Cooling Fan Relay 1 and Cooling Fan Relays 2 and 3 Command parameters. The parameters should display OFF.
3. Ignition ON, observe that the fan is not activated.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement (Within an Electrical Center) , Relay Replacement (Attached to Wire Harness)

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «COMPONENT CONNECTOR END VIEWS - INDEX»(ref-493129-S29400264122012080800000)
2. «Electrical Center Identification Views»(ref-491213-S19440762712012073000000)

Description and Operation

Cooling Fan Description and Operation (3.0L) , Cooling Fan Description and Operation (2.4L)

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-491170-S23088445062012073000000)
4. «Wiring Repairs»(ref-491170-S24000289392012073000000)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480, P0481, P0691, P0692, P0693, or P0694 should not set. If a DTC is set, refer to «DTC P0480, P0481, P0691, P0692, P0693, or P0694 (LFW)»(ref-491221-S21396474462012073000000) , «DTC P0480, P0481, P0691, P0692, P0693, or P0694 (LEA)»(ref-491221-S17712502082012073000000) .
2. Command the cooling fan ON and OFF at Low and High speed with a scan tool. The cooling fan should turn ON and OFF in each of the commanded states.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(ref-491162-S05710312252012073000000) , «Relay Replacement (Attached to Wire Harness)»(ref-491162-S38963856272012073000000)
2. «Engine Coolant Fan Resistor Replacement (LEA)»(ref-491221-S22843843662012073000000)
3. «Engine Coolant Fan Replacement (LEA)»(ref-491221-S34703948032012073000000) , «Engine Coolant Fan Replacement (LF1 or LFW)»(ref-491221-S26458593542012073000000)

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

1. «COMPONENT CONNECTOR END VIEWS - INDEX»(ref-493129-S29400264122012080800000)
2. «Electrical Center Identification Views»(ref-491213-S19440762712012073000000)

Description and Operation

Cooling Fan Description and Operation (3.0L) , Cooling Fan Description and Operation (2.4L)

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-491170-S23088445062012073000000)
4. «Wiring Repairs»(ref-491170-S24000289392012073000000)

Scan Tool Reference

Control Module References for scan tool information

1. Verify that DTC P0480, P0481, P0691, P0692, P0693, or P0694 is not set. If a DTC is set, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(ref-491140-S28645929192012073000000) .
2. Ignition ON, command the appropriate fan relay ON and OFF with a scan tool. Verify that the fans turn ON and OFF when changing between the commanded states.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(ref-491162-S05710312252012073000000) , «Relay Replacement (Attached to Wire Harness)»(ref-491162-S38963856272012073000000)
2. «Engine Coolant Fan Replacement (LEA)»(ref-491221-S34703948032012073000000) , «Engine Coolant Fan Replacement (LF1 or LFW)»(ref-491221-S26458593542012073000000)

Engine Overheating

Engine Overheating

Loss of Coolant

Loss of Coolant

Electrical Information Reference

1. «Circuit Testing»(ref-491170-S01761107082012073000000)
2. «Connector Repairs»(ref-491170-S29468502572012073000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-491170-S23088445062012073000000)
4. «Wiring Repairs»(ref-491170-S24000289392012073000000)

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Coolant Heater Replacement (LFW)»(ref-491221-S02658547632012073000000) , «Coolant Heater Replacement (LEA)»(ref-491221-S09339534182012073000000)
2. «Coolant Heater Cord Replacement (LFW)»(ref-491221-S04923273852012073000000) , «Coolant Heater Cord Replacement (LAF)»(ref-491221-S42585547682012073000000)

Engine Fails To Reach Normal Operating Temperature

Engine Fails To Reach Normal Operating Temperature

Filling Procedure

1. Raise and support the vehicle.
2. Tighten the radiator drain cock to 2 N.m (18 lb in).
3. Lower the vehicle.
4. Slowly fill the radiator with a 50/50 coolant mixture until the coolant level reaches the base of the radiator surge tank. Refer to «Approximate Fluid Capacities»(ref-491137-S36562290632012073000000) .
5. Allow 30 seconds for the coolant level to stabilize and continue to fill the coolant filler neck until the level stabilizes for at least 2 minutes.
6. Start the engine and allow to the engine to idle in PARK or NEUTRAL with the parking brake engaged.
7. Slowly fill the coolant mixture until the level stabilizes at the base of the radiator surge tank.
8. Install the coolant pressure cap.
9. Raise the engine RPM to 2500 RPM for 30-40 seconds.
10. Shut the engine OFF.
11. Allow the engine to cool, remove coolant fill cap and repeat steps 4-10 until the coolant level has completely stabilized within the radiator surge tank.
12. Inspect the concentration of the engine coolant using the J 26568 Coolant and Battery Fluid Tester.
13. Inspect and if necessary, fill the coolant reservoir bottle as necessary.
14. Rinse away any excess coolant from the engine and the engine compartment
15. Inspect the cooling system for leaks.
16. Top off the radiator surge tank if necessary.

1. Tighten the radiator drain cock to 2 N.m (18 lb in).
2. Install the water pump drain plug and tighten to 10 N.m (89 lb in) if removed during the draining process.
3. Lower the vehicle.
4. Remove radiator inlet hose at the engine. Refer to «Radiator Inlet Hose Replacement (LEA)»(ref-491221-S36124773782012073000000) , «Radiator Inlet Hose Replacement (LF1 or LFW)»(ref-491221-S32308816982012073000000)
5. Slowly add mixture of 50/50 DEX-COOL antifreeze and clean, drinkable water to the engine and radiator. Fill the cooling system as indicated below: When the engine block is not drained, add 1.75 liters (1.85 qts) to the radiator through the radiator inlet hose. When the engine block is drained, add 2.0 liters (2.1 qts) to the engine, then add 1.75 liters (1.85 qts) to the radiator through the radiator inlet hose.
6. Install the radiator inlet hose at the engine. Refer to «Radiator Inlet Hose Replacement (LEA)»(ref-491221-S36124773782012073000000) , «Radiator Inlet Hose Replacement (LF1 or LFW)»(ref-491221-S32308816982012073000000)
7. Slowly add mixture of 50/50 DEX-COOL antifreeze and clean, drinkable water to the surge tank until the coolant level reaches the base of the radiator surge tank. Refer to «Approximate Fluid Capacities»(ref-491137-S36562290632012073000000)
8. Start the engine and check for leaks.
9. Run the engine and cycle the vehicle from idle to 3, 000 RPM in 30 second intervals until the engine cooling fan comes ON, the engine cooling fan turns ON at approximately 102°C (216°F). Repeat this process twice before the engine is turned OFF.
10. Return the engine to idle, and idle for 30 seconds, then turn the engine OFF.
11. Allow the vehicle to cool, before adding additional coolant.
12. Add additional coolant to the surge tank until the level is approximately 13 mm (0.5 in) above the surge tank seam.
13. Install the coolant surge tank cap.

Radiator Cleaning

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.

Scheme 33

Radiator Surge Tank Replacement

Engine Coolant Indicator(s)

LOW COOLANT LEVEL

The IPC illuminates the low coolant warning indicator when any of the following occur

1. The BCM detects a low coolant level condition for at least 30 seconds. The IPC receives a class 2 message from the BCM requesting illumination.
2. The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

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 power cord has a thermal element in the cord end that does not allow current to the heater until the ambient temperature reaches 0°F or -18°C.

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 flows from the radiator outlet and into the water pump inlet. Some coolant flows from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost capability as the coolant warms up.

Coolant also flows from 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 then flows 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.

From the cylinder heads, the coolant flows to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine reaches normal operating temperature, or it will flow through the thermostat and into the radiator where it is cooled. At this point, the coolant flow cycle is completed.

Efficient 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 end 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 end tanks are a molded, high temperature, nylon reinforced plastic material. A high temperature rubber gasket seals the end tank flange edge to the aluminum core. The end 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 utilizes a drain cock for coolant recovery during service. The drain cock is located at the bottom of the right hand or left hand end tank, depending on the powertrain option in the vehicle. 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.

Pressure Cap

The pressure cap seals 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, 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.

Surge Tank

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

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 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. 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 from the drive belt.

Thermostat

The thermostat is a coolant flow control component. Its 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.

Transmission Oil Cooler

The transmission oil cooler is a heat exchanger. It is located inside one of the radiator end tanks. 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.