How does a PCV valve work?

When your vehicle’s engine is running, thousands of small but powerful explosions are occuring that produce different gases. The PCV valve plays a crucial role in redirecting these gases away from the key areas in your engine to keep it from doing damage.

The PCV valve, or positive crankcase ventilation valve, works to recycle the harmful gases created in your car engine’s combustion process, and in doing so protects your vehicle’s crankcase, its oil, the engine, and the environment.

It's an older technology that’s been around since the 1940s, and is still used in most cars today. Let’s take a closer look at what it does, and why it’s so important to know if it’s faulty.

What is a PCV valve?

A PCV valve is a valve that opens or closes due to vacuum pressure created in your vehicle’s crankcase.

It’s made up of a tapered cylindrical metal or plastic centrepiece, which sits inside an outer housing with holes at the top and bottom. The centrepiece is held in place with a tension spring and is opened and closed according to how much gas and therefore pressure is inside the crankcase.

It’s part of a closed system that circulates gas, air, and fuel through your engine that would otherwise be spewed out into the atmosphere.

When your car is idling, the valve stays shut, only letting a small amount of gas out of the crankcase. When you’re driving along, the vacuum created by air coming into the system through the air intake manifold opens the valve to draw more gas through. It’s then fed back into the combustion chamber to be burnt.

What does a PCV valve do?

In short, the PCV valve redirects unwanted and harmful gases away from the engine. When your vehicle’s engine combusts fuel and air inside its cylinders, gases are formed. These are a mixture of unburnt fuel and exhaust, and are known as ‘blow-by’ gases. This is because they ‘blow by’ the piston rings into the crankcase on the downstroke of the pistons.

The valve, which is attached to the crankcase, works to stop any stray engine gases from remaining in the crankcase where they would mix with the oil and form a sludge, which can clog your car’s engine. It also works to relieve pressure in the crankcase, which otherwise would cause oil leaks and damage your engine’s seals.

Where is PCV valve located

The PCV valve location differs from vehicle to vehicle, but it’s generally attached to the valve cover near the air intake. If you’re looking at the crankcase, the valve is attached to a rubber tube that connects to the intake manifold.

How do you know if your PCV valve is bad?

If your PCV valve fails, it generally fails in either the closed or the open position. The closed position means that too much pressure will build up in your crankcase, causing oil leaks and letting the oil become contaminated with gases. If it sticks open, your engine will use a lot more oil and not run as efficiently.

Signs of a bad PCV valve

You may notice different signs if your PCV valve is stuck open or shut. Here’s a quick overview of what to expect in each case:

Symptoms of PCV valve stuck closed

Signs of PCV valve stuck open

What happens if the PCV valve is disconnected?

If your vehicle’s PCV valve gets disconnected it will cause a vacuum leak, and you’re likely to hear whistling or hissing noises coming from your engine. Your engine also won’t perform well as you’ll have air intake problems, resulting in declining idle quality.

While it’s possible for the valve to become damaged or split through wear, a disconnection is unlikely to happen by itself.

How often should you replace the PCV valve?

If your PCV valve cannot be serviced, it should be replaced, however there are no specific intervals of replacement.

Everything you need to know about your engine

If you’ve enjoyed learning more about this impressive but simple piece of machinery, why not check out our other blogs? There’s a great one about how to check your car’s oil, or just have a browse and see what takes your fancy.

And if you have any questions about your car’s PCV valve or think it may need a new one, give us a call at mycar where our friendly team is always happy to get you moving!