Both of my cars leak oil

Question:

Two years ago I purchased a 1980 Corvette with 48,000 miles. The car had not been driven for many years so I had to have the brakes replaced. The shop checked everything over and said it was OK. This fall I went on a 300-mile trip and I used three quarts of oil. There is no oil on the floor pans, the car does not smoke, and there is no visible sign as to where the oil is going.

What should I be looking for?

Also, I just purchased a 1965 Mustang with a 1967 V-8 that I was told had been rebuilt. I find that under the hood everything is covered with oil and oil is sitting on the engine. Where is all of this oil coming from?

Answer:

The solution to both of your problems is simple. The oil disappearing out of the Corvette engine is obviously ending up on top of the Mustang engine. Separate the two cars at night and all will be well.

OK, now that we’ve had our little joke, we’ll switch back to a more serious mode. Losing three quarts of oil over the course of 300 miles is obviously excessive. Though unlikely, make sure the oil is not getting into the coolant. You would readily see it if that much oil was somehow leaking into the coolant system.

Absent a leak, which would also be pretty apparent when you looked at the underside of the car, the only possibility left is that the oil is being burned inside the engine. Normally you would see telltale bluish smoke when you’re burning a quart every 100 miles but this is not always the case. Perform a leak down test on all of the cylinders (or a compression test if you don’t have access to a leak down tester) to help determine the condition of the piston ring to wall sealing capacity. If compression is abnormally low then you very well may have found the source of the problem. Bad valve seals and/or bad valve guides may also be the underlying cause of your high oil consumption.

As for the Mustang, there could be several reasons why oil is all over the engine. Very high crankcase pressure can cause oil to blow out all over the place. When the piston ring to cylinder wall seal is bad you get severe blowby. Instead of containing cylinder pressure in the combustion chamber on the compression stroke, the pressure “blows by” the rings and into the crankcase. This excessive internal pressure will normally cause various of the engine’s seals to fail, allowing oil to escape and make a mess.

Another possible cause of excess crankcase pressure is a blocked PCV system. Good old-fashioned oil leaks from the valve covers, intake manifold, etc. can be the cause or at least contributing factors as well.

Normally we expect oil leaking past gaskets to run down and make a mess on the ground and perhaps the underside of the car but sometimes the extent of the leak and the nature of airflow through the engine compartment can cause much of the escaping oil to be blown all over the place.