Engine Nightmare- Part III

[Robert G.]

Ok, the nail is out of the engine, I was able to get the manifold on without any leaks on the end. I used Fel-Pro gaskets rather than the factory correct ones.

Now the car won't start, possibly due to poor cable connections. We'll worry about that later.

What I want to ask now is where is all my oil going. Way back in 1988 the backside of almost all intake valves were covered with very heavy carbon deposits. I cleaned them all off. This time-no carbon at all. I use/lose a quart of oil every 100 miles. Back when I bought the car I asked an ex-GM mechanic about it and he said don't worry, those big blocks always use oil. I recently asked a GM employee who was involved with engine development and he insists it's the PCV valve. I doubt that very much. I've replaced every external gasket on the car and there are no oil puddles, so I guess it's burning the oil. I'd like the engine experts to weigh in on this and what I can do to remedy it or at least to reach a conclusion.

[William C.]

Re: Engine Nightmare- Part III

I'm not an expert. Back in the 80's I had a 327/350 rebuilt and had the same problem 1 gt. of oil in 100 miles. The problem was the valve guides. Replaced the guides and seals and problem resolved. Maybe, some experts will weigh in.

[Edward J.]

Re: Engine Nightmare- Part III

Bob, I am with Bill, a really sloppy set of valve guides will do this, or the oil scrapper rings on the pistons. Is it possiabilty that the umbrella valve seals used were wrong diameter ?

The PCV will ingest oil if the wrong one was installed.

[Joe R.]

Re: Engine Nightmare- Part III

Robert,

A quart every 100 miles sure sounds excessive to me. You might try running a compression test. If the compression is low, you add oil to the bad cylinder(s) through the spark plug hole. If the compression goes up that means bad rings. If it doesn't go up, you have a valve problem (probably valve seals). I think I have that right!

Joe

[Jack H.]

Re: Engine Nightmare- Part III

Yes, that's the 'poor boys' way to do a leak-down test (feed oil in the cylinder to temporarily 'plug' piston rings) and it CAN provide insight. But, a professional leak-down test (inject compressed air into the cylinder in lieu of a spark plug) can NAIL the sources of compression loss (rings vs. intake valve, vs. exhaust valve)...

[Gene M.]

Re: Engine Nightmare- Part III

Robert,
Back in '88 did you replace the guides? If not the problem is still there. It may be covered up by valve seals but loose is loose and it will still pass oil down the valve stems.

Try Joe's compression check and report back. On startup do you have any blue smoke?

[Edward J.]

Re: Engine Nightmare- Part III

Joe & Jack, Sometimes compression test or great for find weak cylinders (Lower Compression). When theres a problem with oil useage its generally the last ring on the pistion which scraps the oil from the cylinder wall and returns the oil to pan, and you may not have any compression issues because the top two set of rings may be okay.

However when theres a oil useage problem, theres a way to tell and that would the outer edge of the piston or pistons has wetness which is oil, and that is a indicator of the third set of rings being a problem.

[Robert G.]

Re: Engine Nightmare- Part III

I put in the original pcv valve last night and also will do a compression test. I've never thought of a good way to get oil all the way around the rings since the pistons are 45 degrees off vertical and I have no good way to squirt oil into the cylinders. I think a professional leakdown test is best at this point, but if it's the oil control rings, then it won't tell us about that. Compression was ok, not great, the last time I checked it. I can't see any signs of blowby either.

I didn't replace the valve seals or valve guides back in '88, so that problem may still be there. (that's how this project got started- just an inspection of the valves and possible replacement of the valve seals). The back side of the valves looked pretty clean, which is why I didn't suspect them. I guess when I had the intake off I could have tried pouring oil on the valve stems to see how much got through to the intake ports.

I haven't driven the car much since 1997, so I will have to tread carefully as I give it a 100 mile drive to check the consumption and gas mileage.

[Joe T.]

Re: Engine Nightmare- Part III

If the engine is burning a quart every 100 miles, there has to be some smoke or oily tailpipe? I understand that there are no signs of a leak, but the oil has got to be going somewhere. Burning that much has to leave some visible evidence? Is it an automatic transmission (bad modulators can suck oil into the transamission as I recall?)

[Robert G.]

Re: Engine Nightmare- Part III

I'll try to get it on the road this summer-it's been 6 years. Right now, the plugs are sooty, so it's running rich. Nothing oily and the exhaust pipes are sooty too, but nothing wet. I think the engine is probably in need of a rebuild.
Compression testing and vacuum tests were ok, not great.
This website has great vacuum diagnostics information:

www.secondchancegarage.com/public/186.cfm

[Joe L.]

Re: Engine Nightmare- Part III

Ok, the nail is out of the engine, I was able to get the manifold on without any leaks on the end. I used Fel-Pro gaskets rather than the factory correct ones.

Now the car won't start, possibly due to poor cable connections. We'll worry about that later.

What I want to ask now is where is all my oil going. Way back in 1988 the backside of almost all intake valves were covered with very heavy carbon deposits. I cleaned them all off. This time-no carbon at all. I use/lose a quart of oil every 100 miles. Back when I bought the car I asked an ex-GM mechanic about it and he said don't worry, those big blocks always use oil. I recently asked a GM employee who was involved with engine development and he insists it's the PCV valve. I doubt that very much. I've replaced every external gasket on the car and there are no oil puddles, so I guess it's burning the oil. I'd like the engine experts to weigh in on this and what I can do to remedy it or at least to reach a conclusion.

Robert------


With this kind of consumption I'd expect one of the following:

1) Oil being drawn from the lifter valley via a poor seal at the bottom of the intake gaskets. This can be due to improper angular relationship between the head and manifold in turn due to head or manifold machining;

2) A problem with the PCV system. A lot of oil can be drawn through a PCV system.

[Robert G.]

Re: Engine Nightmare- Part III

Joe,
I've put in the original pcv valve that came with the car, which is the correct one, and I've replaced the gaskets. I had been concerned about the relationship between the manifold and the heads (after reading about a post you made several years ago) and the condition of the valve stems and seals, which is why I took the intake off in the first place. I could detect no problem with the gaskets, though I had used so much gasket sealant the first time I did this 20 years ago that they pretty much shredded as I removed the manifold.

Now that I'm back in running order I can get the car on the road and see if it's still happening. I have a junker that burns a quart every 200 miles and the smoke coming out of the pcv opening in the valve cover is quite noticeable, so I don't understand where all the oil is going on the vette. A leak should result in a puddle on the ground or the entire underside should be sprayed with a coating of oil if it's happening while running.