Crankcase Ventilation System Description: Notes

A closed crankcase ventilation system is used in order to provide a more complete scavenging of crankcase vapors. Fresh air from the throttle body is supplied to the crankcase, mixed with the blow-by vapors and then passed through a crankcase ventilation valve and into the intake manifold. The primary component in the positive crankcase ventilation (PCV) system is the PCV valve, the valve meters the flow of blow-by vapors at a certain rate depending on manifold vacuum. To maintain idle quality, the PCV valve restricts the vapor flow when manifold vacuum is high. If abnormal operating conditions arise, the PCV system is designed to allow excessive amounts of blow-by vapors to back flow through the crankcase vent tube and into the engine air inlet to be consumed be normal combustion. The engine ventilation system was developed to minimize oil consumption and ensure that oil ingestion could not occur during vehicle limit handling maneuvers.