oil burn after engine warms up

[silvergig]

This was in the regular Mustang forum, should have been here. Sorry guys....


Hello, I'm working on a '65 Mustang with a 302 engine, somewhere between 380-400 horsepower, (performer rpm cam, intake and heads, 9:5:1 compression), Holley fuel-injection. Engine has about 500 miles on it, and is built on a Jasper class II shortblock, (i.e. - it was built by someone who knew what they were doing

I'm trying to find an oil burning problem. The engine doesn't throw any blue on start-up, but will gradually start to blow blue smoke out one pipe as the engine warms up. It didn't do this after it was built. Sometimes the smoke is just a little, sometimes it is a lot. I can really get it going sometimes by turning on the air-conditioner and loading it down at idle. I've added an oil/air separator to the PCV system, with little change. Which valvecover should the pcv/oil/air separator be in? I'm pulling about 14 inches of fairly steady vacuum with the fuel injection, which is pretty good for such a radical camshaft. I'm running 15w-50 mobile 1 performance synthetic for oil. Compression looked good across all of the cylinders when I last checked. I'm pretty easy on this engine, rev-limited to 6000 rpm, never race. Just like to cruise around town every so often.

My current ideas are:

PCV issue
Intake manifold gasket.

I would really like to think that the rings are okay, if I had broken a ring, I should be seeing blue smoke all of the time, right? I should also see a drastic change in compression on that cylinder, correct?

Any ideas would be greatly appreciated!

- Eric

[Mendari]

Originally Posted by silvergig

Compression looked good across all of the cylinders when I last checked. ... I would really like to think that the rings are okay, if I had broken a ring, I should be seeing blue smoke all of the time, right? I should also see a drastic change in compression on that cylinder, correct?

You're right. Compression would be wonky on the bad cylinder. Is it possible that oil is leaking from the cylinder head down into the exhaust valve instead of from the crankcase up into the cylinder?
Try testing this by steadily holding the engine at different RPMs. Start at idle and slowly step it up in 500 RPM increments.

The key is to replicate the problem. We have a saying in the Software industry... "If you're testing for bugs and can't find them, it doesn't mean that the software is bug free. It just means that you're not testing hard enough". This applies to the engine in question because it is burning oil, we just don't know where it's happening, yet.
Good Luck.

[carnut]

I have a similar problem on my 302. I have the same 14 inch vacuum at idle, but with a 600 Holley and a mild Crane hydraulic roller cam. I tried two breathers, one breather and one PCV valve and now two PCV valves, still the same. It only smokes heavily when I get on it in first and second gear. One of my gearhead buddies said it might be piston slap. My compression is 130 lbs. on all eight cylinders. A Ford website noticed a lot of blow by on a racing motor and was told to try a vacuum pump, but being that mine is just a mild street motor, I'm looking into the vacuum theory through other avenues. Good luck.

[silvergig]

I feel sheepish today, because I found the problem - loose intake manifold bolts. 4 of them had come loose. I carefully retorqued them down, and the smoke went away. I'm going to watch them now for awhile and if they loosen again. Looking at Edelbrocks' website, they recommend certain gaskets for aluminum intakes. I will have to check that to make sure the right gasket is under there.

Makes sense. Idle = high vacuum. The high vacuum in the cylinder allows the leak in the intake to suck oil from the lifter valley right into the cylinders. That's why the compression checks out, but the engine is burning oil anyway.

- Eric