Positive Crankcase Ventilation: Description and Operation

PURPOSE
The Positive Crankcase Ventilation (PCV) system is a closed ventilation system that is designed to prevent crankcase fumes or combustion gases from escaping through the engine oil filler cap to the atmosphere.

Typical PCV Air Flow Diagram:

OPERATION
The ventilation process is as follows:
- The crankcase control system controls these fumes or vapors (blow by) by directing them back into the engine where they are consumed in the normal combustion process.
- The crankcase ventilating vacuum source is the upper intake manifold.
- The fresh air passes through the engine air cleaner and then through the crankcase ventilation tubes which connect to the valve covers.
- Ventilating air moves through the crankcase ventilation tubes and down through the oil return passage into the lower crankcase.
- The air and crankcase gas mixture flows from the crankcase through the oil separator and oil separator hose to the PCV valve and then into the upper intake manifold.