87kevroc

I have what I believe to be an intake manifold leak that is causing me to burn a lot of oil, about a quart every thousand miles. I had the engine rebuilt a little over a year ago and as part of the rebuild the machine shop tanked and installed the intake manifold before delivering the engine to the mechanic for installation. They re-installed the intake gasket a month or so after the rebuild but I’m still burning oil.

Also, every few weeks I have to remove and clean the spark plug in number 1 cylinder. It appears this is where the oil is being burned. I did that tonight and noticed that instead of the entire electrode being loaded with what looks like burned oil, just one side of it has deposits on it. The other side of the electrode looks normal, a nice light tan color with no deposits.

Does this confirm my belief that the source of the oil is a leaking intake gasket, or give any other clue as to the source of the oil? Would a compression check help isolate the source? Thanks.

Edit: It's an 87 IROC L98


[This message has been edited by 87kevroc (edited December 06, 2001).]

iroc5speed

sounds like valve seals to me, donesn't sound like the intake is leaking at all

87kevroc

I can’t rule out the valve seals being the problem, but I don’t think that is where the oil’s coming from. If it were the seals, oil would continue to leak into the cylinder after shut off and I’d get a cloud of smoke on startup. The car does not smoke on startup, or any other time, but the exhaust sure smells like it’s burning oil. Also, the large amount of oil being consumed would tend to indicate some other source.

Pukka

Intake manifold gaskets are on the top of the block between the heads. I don't think its possible for this type of leak to form oil deposits that close to your spark plugs.

Most common oil leaks from intake manifolds are the front and back of the block.

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RB83L69

It is definitely possible for the intake manifold to leak oil into the cylinder; the bottom of each port is in direct contact with the crankcase. A gasket failure there will leak oil directly into the intake runner.

The oil from valve guides reaches the plugs by exactly the same path that oil from a bad intake gasket would. You couldn't tell by looking at the plug which source it came from.

A compression check might help identify whether you had a bad compression ring, or a damaged cylinder wall. It would be possible for an engine to test good that way but still have an oil control problem, especially a new one. An old worn out one might not do that, but an oil ring fornicated during assembly underneath 2 good compression rings might fool you.

Just swap the intake gasket and see what you've got. It's cheap and fairly easy.

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