Wednesday, August 16, 2017 Detailed Auto Topics
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Recent model General Motors engines have more than their share of oil leaks. The Generation III and IV V-8 engines are notorious for oil spots. A little known technical service bulletin sheds some light on one issue.

Rear main seal cover plate leaks

A leaking rear main seal cover

Not only are the oil-leaks a nuisance, leaking oil sometimes damages the rubber suspension components. The 5.3, 5.7, 6.0, 6.2 and 7.0 liter GM engines often leak at the rear main seal area. Technically the seal itself is usually not the culprit. General Motors uses a cover plate, on the rear of the engine, in which they mount the seal.

Defective castings of engine blocks and these covers, often result in major oil leaks. From 2004 through 2011, many of these engines left the factory with casting pits in the area where the rear cover attaches. The gasket can usually seal the oil, at least through the warranty period.

Repair involves removing the transmission from the vehicle. With the transmission removed, we take off the flexplate. On the rear of the engine, is a cover, attached by twelve bolts. They press the rear main seal into this cover.

Pitted castings in the cover and engine block on GM enignes

Remove the cover and inspect the mounting surface. If pitting is present, from a poor casting, we need to replace the cover. The GM replacement is part number 12633579. A pitted engine block is as common, but would be very expensive to replace. According the technical service bulletin 05-06-01-034L, GM feels RTV-sealant is acceptable as a repair.

At this time, beyond replacement of the gasket and seal, if the vehicle is in the warranty, GM offers no further assistance. If the vehicle is out of their warranty, as most are, the owner is on their own, as far as paying for repair.

Oil pan gaskets

Oil pan just starting to leak

While the transmission is out, the oil pan gasket should also be closely checked. These gaskets are also bad about failing and leak in the same area. Replacing the oil pan gasket is much easier with the transmission out. Because of the high failure rate, replacing the oil pan gasket, is a wise precaution, when having the rear cover repaired.

Oil-cooler block-off plate

Oil cooler block off plate gasket

Just above the oil filter, on the rear driver-side of the engine, is another common leak point. If the engine has an oil cooler, this is where it attaches. Engines without the oil cooler have a small block off plate, attached by two bolts. Replace this gasket also, to avoid a future leak. They too are a notorious leak point. The gasket is inexpensive and replacement is easy.

Donít be misled by the oil pressure sender unit leak

Rear view of major leakage points

The sender unit for the oil pressure gauge, is at the rear of the engine, mounted between the cylinder-heads. Oil leaking from the sender will run down the back of the engine. This often gives the appearance of a rear main seal leak, as both drip in the same spot. Always inspect the area above the bell housing, to see if oil is present. Oil above the bell housing means the leak is running down from higher on the engine.

As with the other issues, the sender units are common failure items. We can often trace an oil pressure gauge that drops to zero or pegs at maximum, to these parts. Unfortunately, the replacement is not better than the original and often fails within days of replacement. The only fix is to replace it again.

Before your General Motors vehicle gets out of their warranty, having a Pre-warranty Expiration Inspection, by an independent shop, is a good idea. Often, evidence of these leaks may show up in an inspection, before we otherwise note them. This may help the owner avoid paying for a major repair.





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