Crankcase Ventilation System Description: Operation

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Crankcase Ventilation System Components

Courtesy of GENERAL MOTORS CORP.

Callout	Component Name
1	Intake Manifold
2	Low Pressure Chamber
3	Engine Blow-By Gases from Crankcase
4	Lower O-Ring, PCV Valve
5	Upper O-Ring, PCV Valve
6	PCV Valve
7	PCV Hose

The primary control of engine crankcase blow-by gas is the PCV valve. The PCV valve meters the flow of blow-by gas according to the manifold vacuum signal.

The section of the PCV valve that is below the lower O-ring is exposed to manifold vacuum, The section that is between the lower and upper O-rings is exposed to crankcase gases. The PCV valve allows some vacuum pressure to pass thru the valve internal orifice and create a low pressure condition in the crankcase. The blow-by gases in the crankcase are then drawn into the intake system and consumed in the normal combustion process. The volume of blow-by gas entering the intake manifold is precisely controlled In order to maintain idle quality. The correct PCV valve with the proper calibration must be used. The relationship between the flow of blow-by gas and the engine manifold vacuum is charted in the following table:

PCV Valve Operation

Manifold Vacuum	PCV Valve Opening	Blow-by Gas Flow
Low	Large	High
High	Small	Low