Engine Oil Cooler

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

Warnings

Tools required

Parts

• Engine oil cooler assembly × 1 — Use OEM or quality aftermarket
• Oil cooler gaskets/O-rings × 1 — Usually included with cooler
• Engine oil filter × 1 — Use quality diesel-rated filter
• Coolant (as needed for top-off) × 1 — Match existing coolant type

Fluids

• 15W-40 diesel engine oil — 2 qt
• Ethylene glycol 50/50 coolant — 4 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely (minimum 2 hours)
3. Disconnect negative battery cable
4. Remove engine cover if equipped
5. Place large drain pan under engine oil drain plug and oil filter area

Procedure

1. 1

   Drain engine coolant
   Open the radiator drain petcock at the bottom of the radiator and drain coolant into a suitable container. If equipped, also remove the coolant drain plug from the engine block for complete drainage. Allow coolant to drain completely.
   Torque spec

   Drain Petcock7 Nm (5 lb-ft)

   Coolant Drain Plug15 Nm (11 lb-ft)
2. 2

   Drain engine oil
   Remove the engine oil drain plug and drain oil into a suitable container. Allow oil to drain completely. This step is prudent because the oil cooler housing retains both engine oil and coolant that can spill during removal.
   ⚠Ensure drain pan is positioned to catch all oil as the cooler will drain when removed.
3. 3

   Remove oil filter
   Use an oil filter wrench to remove the engine oil filter. Position drain pan to catch oil that will drain from the filter housing. The oil cooler is integrated with the oil filter housing/lube filter head on the passenger's side of the engine block.
   ℹ️Note the orientation of the oil filter for proper reinstallation.
4. 4

   Disconnect coolant lines
   Locate the coolant inlet and outlet lines connected to the oil cooler. Loosen the hose clamps and carefully disconnect the coolant hoses from the oil cooler. Be prepared for residual coolant to drain. Inspect hoses for cracks or deterioration and replace if necessary.
   ⚠Coolant hoses may be brittle on older vehicles. Use care when removing to avoid breaking hose connections.
   Torque spec

   Hose Clamps3 Nm (2 lb-ft)
5. 5

   Remove oil cooler mounting bolts
   Locate and remove the oil cooler cover/housing bolts that secure the oil cooler assembly to the block. Refer to the factory service manual for the exact bolt count and pattern for your engine variant (12-valve vs 24-valve differ). Keep track of bolt locations as lengths may vary.
6. 6

   Remove oil cooler assembly
   Carefully pull the oil cooler assembly away from the engine block. You may need to gently twist or use a small pry bar to break the gasket seal. Be careful not to damage the sealing surface on the engine block. Allow any remaining oil to drain into your catch pan.
   ⚠Do not pry against machined sealing surfaces. Only pry against casting surfaces or mounting boss areas.
7. 7

   Clean mounting surfaces
   Thoroughly clean the oil cooler mounting surface on the engine block using a gasket scraper and wire brush. Remove all traces of old gasket material, oil residue, and debris. The surface must be completely clean and smooth for proper sealing. Clean the coolant hose connections as well.
   ℹ️Avoid using abrasive pads that could score the sealing surface. Use plastic scrapers on machined aluminum surfaces.
8. 8

   Prepare new oil cooler
   Unpack the new oil cooler assembly and verify it matches the old unit. Install new O-rings or gaskets onto the new cooler, lightly lubricating them with clean engine oil. Ensure all sealing surfaces on the new cooler are clean and free of debris.
   ℹ️Compare old and new coolers side-by-side to ensure correct replacement part before installation.
9. 9

   Install new oil cooler
   Position the new oil cooler assembly onto the engine block, carefully aligning the mounting holes and ensuring gaskets are properly seated. Start all housing bolts by hand to ensure proper threading and alignment, then tighten in a crosswise pattern to the factory-specified torque (typically ~18 ft-lbs for M8 fasteners — verify against service manual).
   ⚠Do not force bolts. If resistance is felt, remove and check for proper alignment or cross-threading.
10. 10

    Reconnect coolant lines
    Reconnect the coolant inlet and outlet hoses to the oil cooler. Ensure hoses are fully seated onto the connections. Install hose clamps and position them properly over the hose bead. Tighten clamps securely but avoid overtightening which can cut into hoses.
    Torque spec

    Hose Clamps3 Nm (2 lb-ft)
11. 11

    Install new oil filter
    Install a new oil filter. Lightly oil the filter gasket with clean engine oil before installation. Hand-tighten the filter according to instructions on the filter (typically 3/4 turn after gasket contact).
    ℹ️Do not use an oil filter wrench to tighten. Over-tightening can damage the filter gasket and cause leaks.
12. 12

    Refill engine oil
    Reinstall the engine oil drain plug and torque to specification. Refill the engine with the appropriate amount of 15W-40 diesel engine oil (approximately 11 quarts total capacity with filter — verify against your specific engine build). Check dipstick to verify proper level.
    ℹ️Account for oil retained in oil cooler and filter when refilling. Check level after running engine.
13. 13

    Refill coolant system
    Close radiator drain petcock and reinstall coolant drain plug if removed. Fill the cooling system with the appropriate coolant type through the radiator cap. Fill slowly to allow air to escape. Top off to proper level.
    ⚠Use only the correct coolant type for your vehicle year. Mixing coolant types can cause damage.
    Torque spec

    Drain Petcock7 Nm (5 lb-ft)

    Coolant Drain Plug15 Nm (11 lb-ft)
14. 14

    Bleed cooling system and check for leaks
    With radiator cap still off, start the engine and allow it to warm up to operating temperature. Watch for coolant circulation and top off as needed. Squeeze upper radiator hose to help purge air bubbles. Once the thermostat opens and coolant circulates, top off and install radiator cap. Check all connections around the oil cooler for oil and coolant leaks.
    ⚠️Keep hands and tools away from moving fan and belts while engine is running.
    ⚠Monitor engine temperature closely during bleeding process. Shut down if overheating occurs.

Reassembly

1. Reinstall engine cover if equipped
2. Reconnect negative battery cable
3. Double-check all connections and fasteners for proper tightness
4. Clean up any spilled fluids from engine and surrounding areas

Verification

• Start engine and verify no oil leaks around oil cooler housing and oil filter
• Check for coolant leaks at all hose connections while engine is at operating temperature
• Verify engine oil pressure is normal on gauge or warning light is off
• Verify coolant temperature remains in normal operating range
• After initial test run, shut down engine, allow to cool slightly, and recheck oil and coolant levels
• Test drive vehicle and recheck for leaks after 50-100 miles of operation

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