Crankcase Ventilation Systems: Operation

Air enters system through vented oil filler cap and circulates through engine. Ventilated air mixes with crankcase fumes and are drawn into the intake manifold through ventilator valve by intake manifold vacuum. Ventilator valve, located between crankcase and manifold, insures that the air-fuel mixture will not be leaned excessively under conditions of high manifold vacuum during engine idle. At higher engine speeds, manifold vacuum lowers and the regulator valve opens to admit more air flow. At full throttle, excess fumes escape through filler cap.