Q&A

Mailbag: What Does a PCV Valve Do?

Q:

What is the purpose of a PCV valve?

A:

The PCV valve is an important part of your crankshaft ventilation system. It serves a few primary function related to regulating positive crankcase ventilation.

Your vehicle’s PCV valve works by stopping excessive amounts of oil from being drawn out of the crankcase and regulating the amount of vacuum applied to the crankcase. At low rpm, when vacuum is high, the valve closes slightly to reduce airflow. At higher rpm, when vacuum is reduced, the valve opens more to increase airflow.

The valve also acts as a one-way check valve to prevent forced induction or a backfire. In other words, it won’t allow the crankcase to be pressurized.

Here’s a useful diagram of a PCV valve working at low rpm, high rpm, and during a backfire event:

Image/Summit Racing

Now you know what a PCV valve does, but you might be wondering how it affects vehicle performance. The valve controls the PCV system, which—when properly maintained—can help the engine generate a little more power.

The slight vacuum in the crankcase improves the seal of the piston rings and valve stems, which keeps the compression in the chamber at the desired level. A PCV system also reduces windage and oil aeration, which can cause drag on the rotating assembly and rob your ride of some of its power.

Follow your maintenance schedule and make sure the PCV valve and hoses stay clean and clear to extend the life of your oil and engine.

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