2004 2005 6.6L LLY Engine Oil Leak at Rear Housing Cover Bolt - kw C4500 C5500 diesel GMT800 GMT560 flywheel housing rear main seal

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

04 05 6.6L LLY engine oil leak at rear housing cover bolt. There may be Porosity in the block drillings between the rear main bearing cap side bolt bore and the flywheel housing bolt bore. This can cause leakage from the flywheel housing cover area.

If the leak is found coming from the flywheel housing cover area the oil may be coming from the flywheel housing to block retaining bolts. These bolts are the second bolt from the bottom when viewing the flywheel housing from the back. The lowest (first bolt from the bottom) flywheel housing bolts go into the upper oil pan.

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1. 1. Remove the rearmost main bearing cap side bolt on the same side of the engine where the leakage at flywheel housing bolt is noted.
2. 2. Properly clean and degrease the engine block side bolt holes, flywheel housing bolt bores, rear housing cover bolts, and rear housing cover. Use GM P/N 12377981 brake cleaner or equivalent.
3. 3. Dry the area with compressed air.
4. 4. Use pipe sealer part number 12346004 (in Canada, 10953480) on the threads and the flanges of the bolts.
5. 5. After the flanges and the threads of the bolts have sealer on them reinstall the bolts and torque to proper specifications.
6. 6. Let sealer dry 4 to 6 hours and then evaluate leak.

Note: If the rear housing cover has already been removed reinstall the flywheel housing cover as directed in SI. Be sure to add pipe sealer to the lower flywheel housing cover bolts and the main bearing cap side bolt as described above.

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

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(04 05 C2 C3 K2 K3 6.6 LLY Chevrolet Silverado GMC Sierra) and (04 05 C4 C5 E4 E5 D4 D5 6.6 LLY Chevrolet Kodiak GMC Topkick)