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Oil Filler Necks

I have a 2002 Chevy Tahoe, 5.3L. It has been losing oil between changes and I have to add about 1.5 to 2 quarts every 1500-2000 miles. We cannot physically find the leak and have never had oil spots on the driveway. When doing some recent repairs to the water pump, I noticed a black buildup sprayed from the base of the oil filler neck. The tube has always been loose, but I have never lost pressure so never thought anything of it. In doing some research, I see that there are a few things that can be done: an o-ring inside the oil filler neck can be replaced, the tube can be replaced, or the whole filler neck can be done away with and the cap can be screwed directly into the engine. Just wanted to hear some feedback before I order some parts or melt my cap to the engine.

Love my truck and want it running as long as I can!

I’d repair it to stock, either new O ring or O ring + filler neck.

Check the PCV system: the valve and make sure there’s vacuum present in the hose to it.
If the crankcase is pressurizing oil will leak out of places it wouldn’t normally.
However, I think if you were losing quarts of oil from around the filler there would be more than black buildup.
It would be wet with oil in the area.
It might be burning the oil. 1qt/1000 miles is not desirable, but not unusual for a high mileage engine.

Thanks. It has about 200,000 miles now, so I expect to lose some oil. We switched to full synthetic a few years ago.

What viscosity are you using, and what did Chevy originally recommend?
Unless you’re in a very cold climate I wouldn’t use anything thinner than 5w-30 at this point in the engine’s life.