Engine Oil Cooler

This procedure covers removal and replacement of the engine oil cooler on the 5.9L Cummins diesel engine, including coolant and oil system drainage and refill.

Warnings

Tools required

Parts

• Engine oil cooler assembly × 1 — Use OEM specification
• Oil cooler gasket/seal kit × 1 — Use OEM specification
• Engine oil filter × 1 — Cummins 3101869 or equivalent
• Coolant hose clamps (if damaged) × 2 — As needed

Fluids

• 15W-40 diesel oil or 5W-40 synthetic — 12 qt
• HOAT coolant 50/50 — 4 qt

Preparation

1. Ensure engine is completely cool to the touch
2. Park vehicle on level ground and engage parking brake
3. Disconnect negative battery cable
4. Place large drain pans under engine to catch oil and coolant
5. Remove engine cover or beauty cover if equipped
6. Locate the oil cooler on the driver side of the engine block, below the fuel filter housing

Procedure

1. 1

   Drain engine oil
   Remove the oil drain plug from the oil pan and drain engine oil completely into a suitable container. Once drained, reinstall the drain plug. This reduces the amount of oil that will spill during oil cooler removal.
2. 2

   Drain cooling system
   Open the radiator petcock or remove the lower radiator hose to drain coolant into an appropriate container. Drain enough coolant to bring the level below the oil cooler inlet and outlet connections. This is approximately 4-6 quarts.
3. 3

   Remove oil filter
   Using an oil filter wrench, remove the engine oil filter. Position a drain pan beneath the filter as residual oil will drain out. This provides better access to the oil cooler and prevents contamination during removal. Engine oil filter (verify correct part; Fleetguard LF3894 or LF16035 for the 5.9L Cummins, or OEM equivalent)
4. 4

   Disconnect coolant lines from oil cooler
   Locate the coolant inlet and outlet hoses connected to the oil cooler housing. Using hose clamp pliers or a screwdriver, loosen the hose clamps and carefully slide them back on the hoses. Twist and pull the hoses off the oil cooler fittings. Have shop towels ready to catch residual coolant. Inspect hoses for cracks or deterioration.
5. 5

   Disconnect oil supply and return lines
   The 5.9L Cummins oil cooler bundle mounts inside its housing on the block and uses internal oil passages rather than external oil supply and return lines, so there are typically no separate threaded oil lines to disconnect. Verify against the service manual whether your configuration routes oil through the housing internally before proceeding.
6. 6

   Remove oil cooler mounting fasteners
   Locate the bolts securing the oil cooler assembly to the engine block (typically 2-4 bolts depending on configuration). Using a socket or wrench, remove all mounting bolts. Support the oil cooler as you remove the last bolt to prevent it from falling.
7. 7

   Remove oil cooler assembly
   Carefully pull the oil cooler assembly away from the engine block. You may need to gently pry or wiggle it to break the gasket seal. Be careful not to damage the mounting surface on the engine block. Remove the old gasket material from both the oil cooler mounting surface and the engine block.
8. 8

   Clean mounting surfaces
   Using a gasket scraper and shop towels, thoroughly clean all gasket material and residue from the engine block mounting surface and oil cooler mating surface (if reusing housing). Ensure surfaces are completely clean, dry, and free of debris. Any contamination can cause leaks.
9. 9

   Install new oil cooler gaskets
   Install new gaskets or O-rings onto the replacement oil cooler assembly according to the gasket kit instructions. Ensure all sealing surfaces are properly positioned and gaskets are seated correctly in their grooves. Apply a light coat of engine oil to rubber O-rings to aid installation and sealing.
10. 10

    Install new oil cooler assembly
    Carefully position the new oil cooler assembly onto the engine block, aligning it with the mounting holes and oil/coolant ports. Ensure gaskets remain properly seated during installation. Thread in the mounting bolts by hand first to ensure proper alignment.
11. 11

    Torque oil cooler mounting bolts
    Tighten the oil cooler mounting bolts in a crisscross pattern to ensure even seating. Torque the oil cooler mounting bolts to the factory specification (verify in the service manual; typical M8 fasteners are approximately 18 ft-lbs), tightening in a crisscross pattern and being careful not to overtighten and crack the housing. Verify proper seating and no gaps.
12. 12

    Reconnect oil supply and return lines
    Reconnect the oil supply and return lines to the new oil cooler, ensuring threads are clean and undamaged. Thread fittings by hand first to prevent cross-threading. Tighten securely with wrenches, being careful not to overtighten aluminum fittings.
13. 13

    Reconnect coolant hoses
    Reconnect the coolant inlet and outlet hoses to the oil cooler fittings. Ensure hoses are fully seated onto the fittings. Position hose clamps over the hose connections and tighten securely. Replace clamps if they are damaged or corroded.
14. 14

    Install new oil filter and refill engine oil
    Install a new oil filter after lubricating the gasket with clean engine oil. Hand-tighten the filter according to manufacturer instructions (typically 3/4 turn after gasket contact). Refill the engine with approximately 12 quarts (verify against the dipstick and factory spec) of 15W-40 diesel oil or 5W-40 synthetic oil through the oil fill cap.
15. 15

    Refill cooling system
    Close the radiator petcock or reinstall the lower radiator hose if removed. Refill the cooling system with HOAT 50/50 coolant mixture. Fill the radiator and overflow tank to proper levels. Leave the radiator cap off for now to allow air bleeding.

Reassembly

1. Reinstall engine cover or beauty cover if removed
2. Reconnect negative battery cable
3. Double-check all connections for proper tightness and alignment

Verification

• Start engine and allow it to reach operating temperature while monitoring for leaks around the oil cooler connections
• Check for oil leaks at the oil supply/return lines and oil cooler mounting surfaces
• Check for coolant leaks at the coolant hose connections and oil cooler housing
• Monitor engine oil pressure gauge to ensure normal pressure readings
• Check engine temperature gauge for normal operating temperature
• After engine reaches operating temperature, shut off and allow to cool slightly, then recheck coolant level and top off as needed
• Bleed any remaining air from cooling system by squeezing upper radiator hose while engine is running and coolant is flowing
• Recheck oil level after engine has run and settled for 5 minutes, top off if needed
• Inspect under vehicle for any fluid drips or leaks after test drive
• Monitor oil pressure and engine temperature during a test drive to ensure proper operation

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