Positive Crankcase Ventilation: Description and Operation

Fig. 55 Typical PCV system:

All engines produce small amounts of blow-by gases which seep past the piston rings and into the crankcase. These blow-by gases are the result of the high pressures developed within the combustion chamber during the combustion process, and contain undesirable pollutants. To prevent blow-by gases from entering the atmosphere while allowing proper crankcase ventilation, all engines use a PCV system.

The PCV system prevents blow-by gases from escaping by routing them through a vacuum controlled ventilating valve and a hose into the intake manifold. The blow-by gases mix with the air/fuel mixture and are burned in the combustion chambers. When the engine is running, fresh air is drawn into the crankcase through a tube or hose connected to the air cleaner housing.