Concern: Engine oil leak on GM 5.3, 5.7, 6.0, 6.2 and 7.0L engines (Vortec Gen III or Gen IV V8, aluminum block). Upon initial diagnosis, it may be determined that the leak is coming from the rear engine cover gasket. However, this condition may be caused by engine block porosity on the sealing surface. This bulletin applies only to engines that feature an aluminum block.
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Follow the steps for Oil leak Diagnosis in the Service Manual to determine the source of the leak. If the leak has been diagnosed as coming from the engine rear cover assembly, refer to the Engine Rear Cover Replacement in the Service Manual and remove the rear cover. Inspect the engine block and rear cover for porosity on the mating surfaces.
If porosity is found on the rear cover, replace the rear cover assembly with GM P/N 12633579. If porosity is found on the engine block, use the following procedure to apply RTV to repair the porosity.
The porosity issue is in the gasket sealing surface at the top of the cover, near the high pressure oil crossover port. The oil leaks past the gasket and runs down the side of the cover, and may appear to be a leak at the T-joint area of the cover. The fix involves replacing the cover with P/N 12633579.
Also, if porosity is found anywhere on the sealing surface of the engine block, use the following procedure to apply RTV to repair the block’s porosity.
Clean any residual oil from the block and cover before applying sealant.
* Wipe a small amount of RTV, GM P/N 12378521 onto the surface using a plastic scraper to fill the porosity.
* Remove any excess RTV material, especially from inside the high pressure oil passage.
* The joint may be closed immediately after applying the RTV. Total joint time after the RTV has been applied must be under 20 minutes.
* Reinstall the rear engine cover assembly using a new gasket and a new crankshaft rear main seal. Be sure to refer to the Service Manual for proper procedures and fastener torque specifications. NOTE: When installing a new rear main seal, the seal is installed to the rear cover. A special nylon installation sleeve is then inserted into the seal prior to installing the rear cover and seal to the block and crankshaft. The nylon sleeve prevents the main seal lip from being distorted (bent) outward.