It seems to be a common known fact that a bad intake gasket causes oil to get into the combustion chamber. i dont doubt this fact, but how the hell does that happen?

 

when you say "intake gasket" are you reffering to the head gasket? head gasket and intake gasket are often times phrases that are interchanged. an intake manifold gasket shouldnt even be getting oil to it. a failed head gasket can allow oil and in some cases, coolant into the combustion chambers.

 

i am very familiar with motors in general and have done several rebuilds. i understand how a head gasket can get oil/water mixed up but a intake gasket only seals air/fuel flow into the head. sometimes they indirectly seal a water passage but oil?? other then a bad PCV valve i dont see how oil gets into the intake, and even then what does the gasket have to do with that? once again i dont doubt that this happens, more experienced people then i have brought it up. just how does it happen?

 

It's not the head to intake manifold gasket that fails, it's the intake plenum gasket that has problems.



That's the lifter valley - you can see holes where the camshaft, pushrods, and lifters all sit when the engine is assembled. Directly on top of those is going to sit the underside of the intake manifold. On an edelbrock or LA style manifold, it's just a solid piece and there's no way for oil to get inside the manifold. On the Magnum barrel intakes the underside of the intake is open because the long individual runners have to be cast and the production methods require being able to work from both sides, so the intake manifold is actually two pieces. Here's a picture of a Magnum intake manifold that has been turned upside down to display Hughes' "fix" for the leaky intake plenum gasket failure:




I've been looking for a better picture that shows the OEM stuff but I can't seem to find it.

Here's the TSB relating to it.

http://home.sc.rr.com/janet/TSB/09-05-00.htm

 

im pretty sure its not oil.. more like crappy blowback from the intake in the cylinder.... ive experienced it before... i forgot how it happens but... it may seem like oil but isnt.. its more watery.. just shoot some throttle body clearn down that beast... should clear part of it up... cause if u look at your TB... it has carbon build up... it could be somthing more complicated like the vaccuum system is blowing oil into the intake... not really sure.. just giving a few ideas

 

f0x672 - The intake plenum gasket failure is very common, especially in pre-2000 magnum motors. It does suck blow-by, but it also sucks oil and oil vapors from the lifter galley among other things. While it may not be, you can almost bank on the intake plenum gasket failing at some point.

 

i am not having this problem but i do have a 1999 5.2 magnum so this interested me seeing other people with that problem.

Horatio, thanks for the detailed and informative explination.

 

No prob.

My 02 360 did it earlier this year, and supposedly they had the problem "fixed" before mine was even made.

~4 hours book time at the local rate of $85/hr plus parts and misc. fees would have been almost $400 to get it fixed. Thank god I got that extended warranty. Used it for the intake as well as the electronic transfer case failing, so I'm about even on it.

 

great explaination Horatio... one thing to add is that when you fix it, make sure you use a felpro gasket... the updated stock ones fail as well (I had 2 of them fail). If you try to do it yourself, there is a DIY thread in the DIY forum on how to do it... check it out. it's easy... well ok mostly easy.

 

Yeah if I was fixing it myself I would have gone with one of the hughes modified manifolds, but since it only cost me $50 I'll just keep it stock for a while. 30k more miles (about a year at the current rate) and I'm out of warranty so then the fun begins.