What Are the Symptoms of a Bad PCV Valve?

by Andrea Stein
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A PCV valve, or Positive Crankcase Ventilation valve, assists with the evacuation of gases from an internal combustion engine’s crankcase. A bad PCV valve can impair a car’s performance and may display certain symptoms indicating it needs service or replacement.

Oil Leakage

A bad PCV valve can cause excessive oil leakage and consumption. A PCV valve helps relieve pressure in the crankcase. If the PCV valve malfunctions, crankcase pressures can increase, forcing oil through seals and gaskets.

Air Filter Contamination

A buildup of pressure in the crankcase due to a faulty PCV valve also pushes water vapor through the breather element. A breather element is a filter used to trap excess oil from the crankcase system. This water vapor, mixed with combustion gases, leaves hydrocarbon and oil deposits on the air filter, which may result in greater fuel consumption and the need to clean or replace the air filter.

Decreased Engine Performance

A bad PCV valve may stick or not close properly. This allows an excess of oxygen to enter the combustion chamber. Excess oxygen dilutes the air/fuel mixture ratio, causing a “rich” fuel mixture. A rich mixture can lead to a build up of back pressure in the exhaust system, which can cause engine stalling and a decrease in overall engine performance.

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