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Figure 1 Use RTV sealant to fill in porosity leak...

Figure 2 Revised Mack 12.0L ASET exhaust manifold...

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We've had complaints of oil leaking from the rear cover area on some late model GM engines. Any ideas?
We've encountered some exhaust manifold leaks on a few Mack 12.0L ASETTM diesel engines, Have you heard of any updates or revisions to these manifolds?

Q: We've had complaints of oil leaking from the rear cover area on some late model GM engines. Any ideas?

    A: The AERA Technical Committee offers the following information regarding a rear engine oil leak on 2003-'06 GM 4.8, 5.3, 5.7, 6.0 and 7.0L engines. Upon initial inspection, this oil leak seems to be coming from the rear cover gasket area. This condition may be the result of engine block porosity on the sealing surface.

If the leak has been identified as coming from the rear cover gasket area, remove the cover area and inspect the cylinder block for any indications of porosity in the sealing areas. If porosity is found anywhere on the sealing surface, use RTV p/n 8-12778-521-0 to fill in these areas.

Wipe a small amount of the RTV sealant onto the surface using a plastic scraper to fill in the porosity holes on the mating surface of cylinder block. Remove any excessive RTV that may have been applied, especially from the high pressure oil passage as shown with arrow in Figure 1. Allow the RTV to cure 10 minutes before installing the rear cover. When installing the rear cover, tighten the engine rear cover bolts to 18 ft. lbs.

Q: We've encountered some exhaust manifold leaks on a few Mack 12.0L ASETTM diesel engines, Have you heard of any updates or revisions to these manifolds?

    A: The AERA Technical Committee offers the following information on revised exhaust manifold sections for 1997-2007 Mack 12.0L ASET™ AI and AMI diesel engines.

A revision has been made to the exhaust manifold sections used on these engines, in which the slip-joint clearances have been reduced to provide improved sealing of exhaust gases. Should exhaust leakage at the manifold slip joints occur, the three manifold sections (see Figure 2 and accompanying chart) should be replaced with the revised manifold sections having the tighter slip-joint tolerance.