Positive Crankcase Ventilation: Description and Operation

PURPOSE
The Positive Crankcase Ventilation (PCV) System prevents blow-by gasses in the crankcase from escaping into the atmosphere.

LOCATION
The PCV Valve is screwed into a vapor separator near the front cylinder head.

OPERATION
During part throttle opening, the manifold vacuum draws fresh air through the tube connected to the air cleaner, into the rocker cover and crankcase, drawing the blow-by gasses through the PCV valve into the intake air stream.

During low vacuum conditions (full throttle or heavy engine load) the manifold vacuum is insufficient to draw the gases through the valve, so the gases flow in the reverse direction, being drawn into the air cleaner and then into the intake air stream.

On engines with excessive blow-by some of the gases will flow into the air cleaner under all conditions.