Engine Maintenance

What is a PCV valve? How to test the PCV valve?

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To keep it short, a PCV valve controls emissions and prevents oil sludge. And you can test it by taking it out and shaking it: if you can’t hear any rattle, it’s probably broken, and you need to replace it.

To find out more about the PCV valve, read on.

PCV stands for positive crankcase ventilation. It’s basically a one-way valve, and it’s attached to your engine’s crankcase. The crankcase holds your motor oil and is located at the bottom of your engine. When your vehicle burns fuel, it produces gases – these gases due to emission standards nowadays cannot be just released.

Besides this, sometimes those gases go between the pistons and into the crankcase. This can lead to a dangerous mix: those gases and your engine’s oil mix and can create corrosive, engine-clogging sludge. Not cool.

So in order to prevent sludge and to protect the environment, the PCV valve was created.

When to replace the PCV valve?

Usually, if its working, everything is alright. Like I said in the beginning of this article, just remove it from the engine and shake it. If you can’t hear any rattle, it’s time to replace it.

But every 30.000 miles or so, on some car models, it makes sense to replace it as a prevention measure. Why? Because it’s dirt cheap and a good way to just avoid any problem altogether.

However, once you spot a symptom (see below) or just have an extra 5 minutes, just take a look at the valve and the hoses surrounding it. They can go bad, and you can get a vacuum leak. You’d want to fix that even if the actual valve is not broken.

What are the symptoms of a bad PCV valve?

There are a lot of symptoms, and some of them might be because of a bad PCV valve, some not. That’s why I recommend actually testing it (shake it!), and inspecting the hoses around it.

Symptoms of a stuck closed PCV valve

  • engine oil leaks
  • moisture and sludge buildup inside the engine
  • low whistling or event a… moaning – like noise
  • failure of one or more oil seals or gaskets (increase in internal engine pressure)

Symptoms of a stuck open PCV valve

  • engine misfire at idle
  • increased oil consumption
  • rough idle
  • spark plugs contaminated with oil
  • hart start-up
  • engine oil in the PCV valve or hose

Please be aware that a PCV valve that is broken as in stuck open, can even trigger the ‘check engine’ light due to the increased airflow. Some computers may blame this on a mass airflow sensor or oxygen sensor. Do check the PCV valve also, I wouldn’t be surprised if you’d find out the MAF or O2 sensors are ok, and the PCV valve decided to break.

The bottom line

Just look up how to take out the PCV valve on your specific car model – google it and if you’re planning to keep that car for a couple of years it may make sense to buy a service manual as it can help you save a lot of cash if you like DIY-ing. It can have a lot of nasty symptoms and sometimes even the computer wrongly blames other parts. This is definitely an easy DIY in most cases, and it can spare you a lot of headaches besides saving you some pretty pennies.

note: if you need to find your engine’s code, you can do so using your VIN number.

Car enthusiast. I am dedicated to maintaining my cars as best as I can. I love things that work, and I love keeping them in a good state.

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