Positive Crankcase Ventilation: Description and Operation

Typical PCV System:

PURPOSE
The Positive Crankcase Ventilation (PCV) system returns harmful combustion blow-by gases from crankcase into air intake for burning with normal air/fuel mixture and maximizes the oil cleanliness by venting moisture and corrosion from the crankcase.


OPERATION
Fresh air from the air cleaner passes through the inlet hose to the crankcase. The fresh air mixes with the crankcase vapors and passes through a PCV valve before being drawn into the intake manifold. Vapors that back up under certain conditions cannot escape from the closed system. If manifold vacuum drops or if the system becomes clogged, extra crankcase vapors will reverse direction. These excess vapors flow back to the air cleaner, instead of passing out of the engine into the atmosphere. Once in the air cleaner, they mix with incoming air and pass through the intake manifold to be burned in the combustion chamber.