Oil Separator/PCV

This procedure covers removal and replacement of the oil separator/PCV valve assembly on the 5.9L Cummins diesel engine to restore proper crankcase ventilation and reduce oil consumption.

Warnings

Tools required

Parts

• Oil separator/PCV valve assembly × 1 — Mopar 68004583AA or equivalent
• Oil separator mounting gasket × 1 — Use OEM specification
• Crankcase breather hose (if damaged) × 1 — Use OEM specification
• Hose clamps (if reusing is not possible) × 2 — Use OEM specification

Preparation

1. Park vehicle on level ground and engage parking brake
2. Allow engine to cool completely (minimum 2 hours)
3. Disconnect negative battery cable to prevent accidental starter engagement
4. Place drain pan under work area to catch any oil spillage
5. Remove engine cover by pulling upward on the front edge to release clips

Procedure

1. 1

   Access the oil separator assembly
   Locate the oil separator/crankcase ventilation assembly on the engine per the factory service manual for the 5.9L Cummins; confirm its exact mounting location and orientation before proceeding. The separator is a cylindrical canister with hoses connected to the top and bottom. Remove any wiring harnesses or cables that may obstruct access by carefully unclipping them from their mounting points.
2. 2

   Disconnect the upper breather hose
   Locate the upper breather hose connecting the oil separator to the intake horn. Use needle-nose pliers to squeeze and slide the hose clamp away from the separator connection point. Twist the hose gently while pulling to disconnect it from the oil separator nipple. Expect a small amount of oil to drain from the hose.
3. 3

   Disconnect the lower oil return hose
   Locate the lower hose that returns oil from the separator to the engine block. Position the drain pan directly beneath this connection. Use pliers to slide the hose clamp back along the hose, then carefully twist and pull the hose off the separator. Allow oil to drain completely from both the hose and separator.
4. 4

   Disconnect the crankcase vent hose
   Identify the crankcase ventilation hose connected to the side or rear of the oil separator assembly. Release the hose clamp and disconnect this hose from the separator. Note the routing of all hoses for proper reinstallation.
5. 5

   Remove separator mounting fasteners
   Locate the mounting bolts or bracket securing the oil separator to the engine or intake. Typically there are two bolts holding a mounting bracket. Use the appropriate socket (usually 10mm or 12mm) to remove these fasteners completely. Support the separator while removing the last fastener.
6. 6

   Remove the oil separator assembly
   Carefully lift the oil separator assembly away from the engine, tilting it to drain any remaining oil into the drain pan. Remove the old mounting gasket from the mating surface on the engine block if applicable. Inspect the separator for excessive sludge buildup or damage that confirms replacement is necessary.
7. 7

   Clean mounting surfaces and inspect hoses
   Use a wire brush to clean the mounting surface on the engine where the separator attaches. Remove all old gasket material and oil residue. Inspect all breather hoses for cracks, collapse, or excessive oil saturation. Replace any damaged hoses. Use compressed air to blow out debris from hose connections if available.
8. 8

   Install new oil separator gasket
   Position the new mounting gasket onto the engine block mounting surface or onto the base of the new oil separator assembly, depending on design. Ensure the gasket is properly aligned with all mounting holes and oil passage openings.
9. 9

   Install new oil separator assembly
   Position the new oil separator assembly onto the mounting location, ensuring the gasket remains properly seated. Align all mounting holes. Thread the mounting bolts by hand to prevent cross-threading, then tighten them evenly in a criss-cross pattern. Since no specific torque value is confirmed, verify the correct spec against factory service documentation before final tightening. For small M6 fasteners approximately 7 ft-lbs is typical, and for M8 fasteners approximately 17 ft-lbs; do not overtighten as the mounting boss may be plastic or aluminum.
10. 10

    Reconnect crankcase vent hose
    Reconnect the crankcase ventilation hose to the appropriate port on the new oil separator. Slide the hose clamp into position approximately 1/4 inch from the end of the hose and tighten securely. Ensure the hose is routed exactly as it was originally to prevent kinking.
11. 11

    Reconnect lower oil return hose
    Connect the lower oil return hose to the bottom of the oil separator, pushing it firmly onto the nipple. Position the hose clamp over the connection point and tighten securely. Verify the hose is seated fully to prevent oil leaks.
12. 12

    Reconnect upper breather hose
    Connect the upper breather hose from the intake horn to the top of the oil separator. Push the hose fully onto the separator nipple and position the hose clamp. Tighten the clamp securely. Double-check that the hose is not kinked or twisted.
13. 13

    Reinstall components and check connections
    Reinstall any wiring harnesses or cables that were moved for access. Verify all three hose connections are tight and properly clamped. Wipe down the assembly and surrounding area to remove any spilled oil, which will make leak detection easier during verification.

Reassembly

1. Reinstall the engine cover by aligning the rear clips first, then pressing down on the front until it clicks into place
2. Reconnect the negative battery cable
3. Verify all tools and parts have been removed from the engine bay

Verification

• Start the engine and allow it to idle for 5 minutes while monitoring the oil separator area for any oil leaks at the hose connections
• Check for proper crankcase ventilation by removing the oil filler cap while engine is idling - there should be minimal pressure release and no excessive blow-by
• Rev the engine to 2000 RPM briefly and recheck all connections for leaks
• Take a short test drive and recheck the oil separator assembly for any seepage or loose connections
• Monitor oil consumption over the next few hundred miles to confirm the repair resolved any excessive consumption issues

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