Positive Crankcase Ventilation: Description and Operation

Typical PCV Air Flow Diagram:

PURPOSE
The crankcase emission control system (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.

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 (ACL) 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.

NOTE: Do not remove the PCV system from the engine. Removal of the PCV system will adversely affect fuel economy and engine ventilation resulting in shorter engine life.