What Is a PCV Valve and How Do You Replace One?
You know that horrible little check engine light that shows up on your dashboard? The one that tells you a problem without telling you what the problem is? If you see this light, or if you notice your engine is idling roughly, or both, you might need to check your PCV valve.
The positive crankcase ventilation valve can get clogged and cause problems. This article will answer questions like what is a PCV valve, what PCV valve symptoms should you watch for, and how can you complete a PCV valve replacement.
What Is a PCV Valve?
The terms "PCV" and "crankcase breather" can be used interchangeably—they refer to the exact same engine part. The PCV stands for "positive crankcase ventilation."
The PCV valve is located inside the engine. Technically, it's part of the carburetor system. The PCV valve is a pipe that releases the gasses trapped in the engine.
Combustion engines create gasses that can escape the piston rings. The crankcase breather routs these gasses back to the carburetor preventing the gasses from escaping into the atmosphere.
Not every car has a PCV valve. If your vehicle doesn't have a carburetor, it doesn't have a PCV valve.
What Does a PCV Valve Do?
The PCV valve is designed to draw leftover gases created during the engine's combustion process and route them back into the engine. The gases get burned up in the combustion chambers.
This is what happens when the system works. When the system doesn't, those gases escape into the atmosphere or into other parts of the engine.
Symptoms of a Bad Crankcase Breather (How to Know When to Replace It)
When the PCV valve, or crankcase breather, is going bad because it's getting too clogged up, there will be symptoms. The check engine light might come on, the idling of the vehicle will be off and you may notice a general roughness in the engine where it doesn't run smoothly.
If the engine is allowed to pressurize, you can lose performance. This is when you'll notice rough idling, indicator lights, and possibly other issues. There will be a difference in the way the car drives. Ultimately, leaving this problem unchecked could lead to much larger engine problems.
When the PCV valve is clogged, the vehicle will consume more oil because of the pressure building up in the engine. The additional pressure might even force oil into seals and gaskets, where it doesn't belong. The air-to-fuel ratio of the engine will be out of whack, so to speak. This is what triggers the check engine light.
It's very easy to confuse the rough idling of the PCV valve with bad spark plugs. Before you replace the plugs, pull and clean the PCV valve and replace it as needed.
If your PCV valve is too far gone to be successfully cleaned up, it will affect engine performance and could cause leaks that end up creating much bigger problems. When the PCV valve is too dirty for air to flow properly even after cleaning, it must be replaced.
Once your PCV valve is pulled, shake it. You should hear a distinct rattle. If you don't hear this rattle even after the valve is cleaned, it's bad. You must toss out the valve and replace it with a brand-new one.
Even if you're not yet having a problem, you should replace the PCV valve every 20,000 to 50,000 miles. As the first sign of engine trouble, check this valve if it hasn't been replaced within 20,000 miles. This could very well be your entire problem.
How to Replace the PCV Valve
If you see that your valve is clogged, you need to take it out and clean it. If this does not work, you will need to replace the entire valve. Luckily, this is not a huge task. Even those who do not have extensive knowledge of vehicles can DIY this project.
Take pictures during every step of this process so you can put everything back the way it was. Work with care. You don't want to end up causing more damage to the engine simply because you weren't paying attention.
The PCV valve is an inexpensive engine part, particularly when compared to the cost of other parts. Typically, you can get a brand-new PCV valve for less than $20.
1. Find the PCV Valve
Locate your vehicle's carburetor and look for a hose connecting the PCV valve. The hose is usually held in place with a clamp. You'll be able to see how the whole PCV valve works at a glance if you follow the hoses.
2. Remove the Air Filter
Remove the entire housing cover, leaving the hose attached, by loosening the fasteners on the cover and lifting it off.
Once you have located the air filter housing, start loosening the fasteners holding the cover of the filter housing. The fasteners of the air filter housing can be a clip, nuts, or wing nuts.
After loosening the fasteners of the cover, you can now pry loose the cover of the air filter housing. Clean the cover with a cloth to remove any debris stuck on the filter. Hang on to those fasteners. You will certainly need them later.
3. Check the PCV Valve Parts
Inspect any and all clamps, nuts, and grommets that held the PCV valve in place. Try to clean off any gunk as best you can.
If these fasteners don't clean up well, replace them. These are very affordable auto parts that are easy to replace, so don't attempt to re-use dirty or gunky parts when you don't have to.
Check all the hoses. Test how flexible they are and blow through them to see if air passes freely through them. If the hoses are nice and flexible, rather than brittle, and the air passes through them easily, keep them. Otherwise, replace these as well.
Shake the valve. You should hear a rattle that is quite distinct. If the sound is muffled or nonexistent, the valve is clogged. The noise of the valve is your best indication of how everything in the vehicle is working together.
Your hoses likewise shouldn't be too soft or spongy in any way. Hoses that are too soft and too flexible are just as useless as the hoses that are too hard and brittle. Again, this is an inexpensive auto part so replacing hoses is no big cost. It only adds a few minutes to your total DIY project.
Take the air filter out. Likely, you'll want to replace this completely. This is an affordable auto part, however, so replacing this is no big expense. You can attempt to clean the filter with a can of air. If it cleans up well, reuse it. Otherwise, toss it. Usually, air filters cannot be salvaged but sometimes it's possible.
4. Clean the PCV Valve
Use auto parts cleaner to try to clean up the valve. This is a simple solution. You simply soak the valve inside the formula so that all that gunk and grime will get pulled off the part.
Follow the directions precisely to have a better chance of successfully cleaning the valve. There should be no hard deposits or buildups of grime on the valve after it has soaked in the solution. If the valve doesn't clean up well, replace it.
You will never get the PCV valve looking perfect no matter how much you do to clean it. However, sometimes these valves can be cleaned and salvaged. Remember that it's the function that matters, not how good your valve looks.
5. Put the PCV Valve Back
Place the valve back into position by hand before you secure it. Don't over-tighten. Be sure to replace the air filter and all hoses, putting everything back exactly the way it was.
6. Check It
Turn on the engine and let it run for a few moments. Check all around the valve for leaks, check the engine dashboard light and let the vehicle idle.
Repair Safety Tips
Let the engine sit while turned off for a couple of hours or so before you work on the vehicle, so it has cooled down when you work on it. Otherwise, you could burn yourself on a hot engine.
Avoid getting any dirt or debris into the air duct while replacing these parts.
Use a cup or can to keep the small screws and fasteners, so they are not misplaced.
Never place anything on the battery because it can react with the battery and can explode.
Once you know how to check and replace your PCV valve, you can replace this part fairly easily, as needed, every 20,000 to 50,000 miles. Do a regular maintenance check on the valve to keep all the air flowing in your engine properly and keep your vehicle functioning well.
For more info check out our pieces on finding and cleaning PCV valves, or branch out into other engine maintenance by learning how to reset a check engine light or troubleshoot a smoking exhaust pipe.