Mailbag: What’s Causing Gasoline to Leak into My Oil?

Q: The 351 Cleveland engine in my 1974 Mercury Cougar is having a power problem. It has an Edelbrock intake manifold with a 600 cfm Holley four-barrel, 2V Cleveland heads, Crane RV-style cam, headers, and a points distributor. Timing is set to factory specs.

I think I can trace the problem to having a little gasoline in my oil. Oil pressure is high initially, then goes to normal as the engine warms up. I am also noticing oil blowby through the valve covers.

With almost 500 miles on the engine, shouldn’t the moly piston rings have seated by now? The engine seemed to make more power when it had the factory two-barrel carb manifold. Could having a four-barrel carburetor with 2V heads be the problem?

A: The oil pressure fluctuation isn’t really a problem, but having gasoline in the oil is. Like you said, the piston rings should have seated by now. Our guess is that because they have not seated, fuel is getting into the cylinders and your crankcase. You should perform a compression test and a leakdown test. The leakdown test will tell you if the rings have seated or not.

You also may be running the wrong intake manifold. Fords are notorious for having many different combinations of blocks, heads, and manifolds. The correct Edelbrock intake for a 351C with 2V heads is EDL-2750. If this is not the manifold you have, it may not be sealing to the block, or the intake gasket may have moved, causing a vacuum leak. That leak could be the source of your poor performance and the fuel in your oil.