The PCV system is beneficial to overall engine health and service life. The PCV valve purges crankcase vapors, which are a mixture of air, oil, moisture, and combustion chamber vapors that escape past the piston rings and imposes a slight vacuum on the crankcase (CC). It helps control moisture accumulation that leads to acid and sludge formation. The PCV valve fits between either valve cover (or the lifter valley roof) and a balanced manifold vacuum port via a reinforced-wall 3/8" rubber hose. The valve body contains a spring-loaded sliding check pintle that regulates the flow of CC vapors into the intake manifold where it mixes with the incoming intake charge for subsequent combustion in the cylinders. The pintle is designed to float between opposing seats against light spring pressure such that it closes toward its inlet (valve cover side) when manifold vacuum is low (e.g., engine off, WOT, and intake backfire) or closes toward its outlet (intake manifold side) when manifold vacuum is greatest (e.g., engine idle RPM and deceleration). The spring modulates the pintle position between its seats according to the pressure differential on either side of the valve, hence PCV valves are calibrated according to application. For the greatest CC ventilation benefit, the PCV valve is inserted into a small baffled chamber in the roof of one valve cover and a vented breather is inserted into a small baffled chamber in the roof of the opposite valve cover. Alternatively, the PCV valve can be centrally located in the lifter valley roof and then both valve covers are vented. The baffled chambers in the roofs of the valve covers help to isolate the valve and breather from direct exposure to liquid oil thrown from rapidly moving valve train components. The best valve cover breathers filter incoming air to minimize oil contamination by abrasive particles. Filters can be internal or external to the breather, however, external filters are more easily serviced. Due to currently governing emissions laws, the OEM plumbing configuration must be maintained.
Fixed orifice CC ventilation is unique to select engine applications such as the Jeep 4.0L inline six. IMO PCV systems are superior since they are dynamic and adjust to variable operating conditions on a real-time basis.
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