Positive Crankcase Ventilation Valve: Description and Operation

The 3.7L V-6 and 4.7L V-8 engines are equipped with a closed crankcase ventilation system. The Positive Crankcase Ventilation (PCV) valve (6) is mounted to the oil filler housing (4).

The PCV valve is sealed to the oil filler housing with an O-ring (1).




Two interconnected breathers (1) threaded into the rear of each cylinder head are used with the system.
The system also includes the air cleaner housing and various tubes and hoses to connect the system components.




A typical enclosed crankcase ventilation system is shown in the graphic.

The PCV system operates by engine intake manifold vacuum. Filtered air is routed into the crankcase through the air cleaner hose. The metered air, along with crankcase vapors, are drawn through the PCV valve (4) and into a passage in the intake manifold. The PCV system manages crankcase pressure and meters blow by gases to the intake system, reducing engine sludge formation.

The PCV valve contains a spring loaded plunger. This plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum.




When the engine is not operating or during an engine pop-back, the spring forces the plunger back against the seat. This will prevent vapors from flowing through the valve.




During periods of high manifold vacuum, such as idle or cruising speeds, vacuum is sufficient to completely compress spring. It will then pull the plunger to the top of the valve. In this position there is minimal vapor flow through the valve.




During periods of moderate manifold vacuum, the plunger is only pulled part way back from inlet. This results in maximum vapor flow through the valve.