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Jim Grant's Tech Tips Chevy S-10, Oil in the Air Cleaner
Q:
I get
oil in the air cleaner of my Chevy S-10 after I use it on the highway.
Was there a change in head gaskets making oil drain holes smaller to keep
heads cooler from the manufacturer? Could that possibly be the problem?
The engine was just rebuilt and the spark plugs are clean, there is no
misfire and the engine runs smooth.
-
Dwayne D.
A:
All
engines have a condition that is called blow-by. Blow-by is the gases
of combustion that get around the piston rings and into the crankcase
of the engine. The Positive Crankcase Ventilation system is designed to
draw these blow-by gases out of the crankcase and burn them in the combustion
process. Simply put, it sucks that bad stuff out and feeds it back to
the engine so it can burn it. The engineers designed the PCV system to
handle a reasonable amount of blow-by gases. But, if the volume of blow-by
is greater than what the PCV system can remove, then the additional gas
is pushed back through the vent side of the system, which happens to be
in the air cleaner housing. You should also know that oil vapors hitch
a ride with the blow-by gases. It is common for carbon deposits to form
in the vacuum passages of the PCV system restricting the flow, resulting
in the vapors being pushed into the air cleaner housing. That’s one
of the reasons PCV valves are serviced/replaced regularly. If the PCV
system is operating correctly and you’re still getting oil building-up
inside the air cleaner housing, then you likely have internal engine problems.
Have the PCV system checked and serviced as needed. If oiling in the air
cleaner housing continues, go back to the engine rebuilder. Why? Something
wasn’t done right.
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