Mailbag: Causes and Cures for Engine Oil Mist
Q: I have a 1955 Chevy with a 383 motor, a four-speed transmission, and a 3.73-geared 12-bolt rear axle. The engine is a four-bolt with nodular iron crank, 9.5:1 compression forged pistons, Airflow Research heads, and Edelbrock Performer RPM intake, a 750 cfm Holley double pumper carburetor, 1 5/8-inch Hooker headers, a hydraulic roller cam (.525-inch lift), and roller rocker arms. The motor has about 2,000 miles on it.
I’ve noticed a slight oil mist coming from the passenger side valve cover breather, while the driver’s side is bone dry. There are rubber baffles molded into the bottom of the breather grommets. What causes this misting (almost like oil smoke)? Shouldn’t both breathers exhibit the same problem?
A: Your breather cap oil problem could be caused by a number of things.
For example, the intake gaskets might not be sealing, and the resulting vacuum leak could be sucking oil into the breathers from the lifter valley. The misting oil could also be due to crankcase windage and the resulting pressure. The pressure will find its own path out of the engine, which may be why one side is misting and not the other. Anything you can do to relieve the crankcase pressure will cut down on the oiling through your breathers. Putting a PCV valve in line to the carburetor would help. We would also do a cylinder leakdown test to verify that the oil control rings are sealing properly in the bores.
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hi have a 400 1969 Pontiac , yd , oil pressure went down, changed oil, cold first start 40+ then as moter reaches temp, goes down to 10/15 . it does go up while shifting , I ran a very heavy oil then the cold hit , I did remove but the problem is still here , replaced filter, could it be the pump, or the pick up blocked, thanks
Generally, when you see a pressure fluctuation when going from cold to hot, it is an oil clearance issue on the main & rod bearings. A blocked pick up tube would show low pressure all the time.