Symptoms of a Bad or Failing Positive Crankcase Ventilation (PCV) Valve

The positive crankcase ventilation (PCV) valve works to evacuate gas from the crankcase of the engine. The PCV valve directs these gases back into the combustion chambers via the intake manifold. This plays a large role in engine efficiency, improving emissions and the overall operation of your vehicle. A bad PCV valve will affect the performance of your vehicle, so there are a few signs to watch out for before the valve completely fails:

1. Excessive oil consumption and leak

A bad PCV valve may have a leak, which will cause excessive oil consumption. In addition, you may also notice oil leaking through the seals and dripping on to the floor of your garage. This is because the pressure in the crankcase may increase when the PCV valve fails, so the oil is pushed out through the seals and gaskets since there's no other way for the pressure to be released. The leak will cause your vehicle to burn oil and leak oil beneath your vehicle. If you notice either of these, consult a professional mechanic to have your PCV valve replaced.

2. Contaminated filter

A filter called a breather element may become contaminated with hydrocarbons and oil once the PCV valve starts failing. This is due to the increased pressure building up in the crankcase, which pushes water vapor through the breather element. The water gets mixed with the gas, which causes the buildup and can increase fuel consumption in your vehicle. One way to check this part is to physically inspect the filter for buildup. Another way is to measure the gas mileage on your vehicle. If it starts to go down seemingly without reason, the PCV valve may be going bad.

3. Overall poor performance

As the PCV valve starts going bad, the performance of your vehicle will get worse. This can be exhibited by a buildup of pressure in the exhaust or the engine could stall out. The bad PCV valve may not close all the way, so oxygen may get into the combustion chamber. When this happens, the fuel and air mixture is diluted causing your vehicle to run poorly and lean out.

If you notice your vehicle is leaking oil, consuming large amounts of oil, you have a contaminated filter, or the car is not working like it should, have the PCV valve looked at and replaced. This will keep your vehicle running smoothly and keep your fuel economy where it should be. YourMechanic makes getting repairs to your positive crankcase ventilation valve easy by coming to your location to diagnose or fix issues. YourMechanic’s experienced technicians are also available for any questions that may arise. You can book a service online 24/7.


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