8.1L oil consumption fix

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jlj1267

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So I’ve been doing a lot of intensive research on the intake manifold/PCV system on these engines. I’m getting fed up with oil consumption and I’d like to share what I’ve found. The intake manifold has an integrated PCV system (no PCV valve), in which crankcase vapors are pushed through a small tube on the belly of the intake. The blow-by gases are pushed into the plenum by air coming into the lifter valley from the PCV inlet port (~1/4” hole in throttle body). GM has used a design like this on many smaller platforms (I believe the late 90’s 3800’s and maybe some version of an Ecotec?) The manifold acts as the oil separator, and in a way serves as a sort of “catch-can”. GM didn’t notice an issue with this design, due to its application being mostly on smaller displacement engines. Gm finally caught the consumption on the 8.1, an issue many 8.1 owners were told wasn’t an issue. GM specifies that oil consumption should not be more than 1qt per 100 gallons of fuel burned. Finally, General Motors caught the problem, and fixed it. So they thought. GM our our a Technical Service Bulletin on the consumption, telling owners to replace intake manifold gaskets and bolts, with updated part numbers. While this slowed consumption, it never fixed it completely. this as a problem. The only way to stop oil from getting into the intake is to run an external PCV system. Some have been able to weld a 45° tube on the small tube under the belly to keep oil from splashing up and being sucked in so easy, but this only slows consumption. Others say you can add a check valve to the tube. But once again, this only slows it. The true fix would be to first, pull the intake, cut the belly open and do the normal modifications inside while you have the manifold off. Next, cut the tube off and weld it shut. On the throttle body, tap the small hole (1/4” NPT) and plug the port. Be careful, the material here is very thin and soft cast aluminum. You must be sure to of course clean the intake spotless before welding it back up and setting it back on top of the engine. As for the PCV, you can either drill the valve cover for a PCV valve, or on the rear of the manifold next to where the EGR housing bolts down, you can weld a bung, and add a PCV valve. Then on the neck of the intake (driver side slightly under throttle body is easiest to access) weld another bung and add hose barb. Run a hose from the barb to the PCV valve either in the valve cover, or the one on the back of the manifold (whichever route you go.) Do not attempt to just “block off” the factory PCV system and run with it!!! In a normal PCV system, a breather on one side of the engine (valve cover), let’s fresh air into the crankcase. The blow-by gases are then flushed out through the PCV valve (check valve) then through a hose into the breather/air filter housing. Just plugging the hole in the throttle body would “seal” the crankcase, and not allow any blow-by gases to be filtered by the PCV then introduces into the intake to be cleanly burned. This can cause major problems. Your oil will sludge much quicker. You may notice excessive engine heat, and noise as well. The PCV system’s sole purpose is to filter blow-by and introduce unburned gases back into the intake, to be burned completely, and cleanly. I hope this clears up a lot of headaches for people. I plan to run tall traditional style Big Block valve covers with PCV grommets, so welding bungs and tapping the intake wouldn’t have to be done. Thanks!
 

Cantrepeat

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I appreciate the information but when you just copy and paste without formatting it makes the post very difficult to read. No offense intended.
 
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jlj1267

jlj1267

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I wonder if this would be a good application for one of those self draining catch cans that return to the oil galley
I have already built a DIY catch can (made mine out of an aluminum water bottle, but a catch can is a lot more effective than just a check-valve.
 
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jlj1267

jlj1267

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I appreciate the information but when you just copy and paste without formatting it makes the post very difficult to read. No offense intended.
I’m sorry it’s all in one giant conglomerate paragraph. I typed this whole thing at 2:00 in the morning and since I’m relatively new to this forum, I couldn’t figure out how to edit my original thread. No offense taken though. Thanks!
 

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