What happens if PCV valve stuck open?

Cars are pretty complicated pieces of machinery, filled with tons of obscure components that you don’t normally think about but can nonetheless drastically affect the driving characteristics of your car. One of these components is the PCV valve.

The PCV (positive crankcase ventilation) valve is used to let gas out of the crankcase. This prevents damage from happening to the various gaskets and seals within the engine and also helps the engine run more efficiently.

In this article, we’ll be going over how a PCV valve works and what the symptoms of a failing PCV valve are, and how you can deal with any PCV valve-related issues you might encounter. 

What Is a PCV Valve, and Where Is It Located?

As we’ve mentioned, the PCV valve is used to vent gas from within the crankcase. However, you might not know why this is necessary to begin with, so allow us to explain.

When fuel is combusted inside your engine, it creates waste gases as a byproduct. Most of these gasses exit the engine via the exhaust, but occasionally these gasses can get past the pistons and make their way into the crankcase where the engine oil is located.

Related: What Happens If You Put Too Much Oil In Your Car

If enough gas gets into the crankcase and mixes with the oil, it’ll create a thick, foul, oily sludge. This sludge is really bad for the engine, as it can corrode parts of the engine or clog up the various oil passages in the system.The PCV valve is a one-way valve that allows any gas that enters the crankcase to return to the engine where it can be burned.

Since about 70% of the waste gas that leaves the engine consists of unburnt fuel, redirecting the gas from the crankcase back into the engine not only helps preserve the condition of the engine oil, but also helps make the engine more fuel efficient.

As for where you can find your PCV valve, this valve is generally located on top of your valve cover where it is easily accessible. Look for a small tube running from the valve cover to the air intake and you’ll probably find it without much trouble. 

It’s important to note that while many modern vehicles have a PCV valve, this isn’t the case for every single vehicle on the road. It may be worth it for you to double-check that your car actually has such a valve before spending too much time looking for it.

Bad PCV Valve Symptoms

If the PCV valve or the hose connected to it breaks, it can potentially cause several symptoms. If you know what to look out for, you can recognize the signs of a bad PCV valve before it causes too much damage to your engine.

Here’s what to look out for when trying to diagnose a bad PCV valve:

Oil Leaks

As you know, the PCV valve lets gas out of the crankcase. If the valve stops working, gas builds up inside the crankcase, which causes its internal pressure to rise. If the pressure inside the crankcase gets high enough, it can actually force engine oil out of the crankcase through the various seals and gaskets.

Take note if you happen to see any oil puddling under your car, and if you do, inspect your engine and crankcase and look for any oil that might be seeping out from under the seals. This could very well be an indicator of a stuck PCV valve. 

Poor Fuel Economy

If the PCV valve gets stuck closed, this can worse your fuel economy. This happens because the PCV valve lets some air into the engine when it is open, which the engine’s computer takes into account. This helps the computer adjust the air/fuel mixture accordingly.

With the PCV valve stuck closed, however, there won’t be enough air getting to the engine, meaning the engine will be running rich. This decreases fuel economy and also increases the amount of emissions that the engine produces.

Smoky, Bluish Exhaust

If the PCV valve gets stuck shut, this will of course cause the pressure to increase within the crankcase. When this happens, oil may leak out through the seals, but it can also sometimes get forced up into the combustion chambers.

If this should occur, the oil will start to burn, which will affect the appearance of the exhaust. Specifically, the exhaust gas will be a lot smokier than normal, and will have a bluish tinge to it. Blue exhaust smoke is the most obvious sign that your engine is burning oil, and you should never ignore the presence of blue exhaust smoke if you notice it. 

Related: Why Is There White Smoke Coming From The Engine?

Engine Misfiring

If the PCV valve gets stuck open, however, this can cause a different set of issues. The most obvious issue this can cause is a misfiring engine, particularly when the engine is at idle.

This happens because a stuck PCV valve will cause too much air to enter the engine. If this happens, the engine will start to run lean, as the air/fuel mixture will contain too much air and not enough fuel.

Related: Symptoms of a Bad Ignition Coil & How to Fix It

If you notice your engine sputtering and hiccupping at idle, this is a sign that something is not quite right with the engine’s combustion, and a bad PCV valve could very well be the source of this.

Strange Engine Noises

If the PCV valve or the valve hose is leaking, the engine might start making strange noises as a result. In particular, you might hear a whistling or a hissing sound coming from under your hood.

This sound is caused by air rushing out of the hole in the valve or the valve hose. Be on the lookout for this or any other unusual sounds coming from your engine, as an abnormal noise almost always means that something is wrong.

Check Engine Light Is On

There are tons of reasons why your check engine light might turn on, and a bad PCV valve is one of them. If your check engine light comes on in combination with some of the other symptoms we’ve mentioned so far, there’s a good chance the PCV valve is the culprit.

Related: What Does The Service Engine Soon Light In My Car Mean?

If you want more confirmation, however, you could try using an OBD-II scanner and see what error codes you get. If you see P0171 or P0174, this indicates a problem with the air/fuel mixture in the engine, which may be caused by a bad PCV valve.

How to Check Your PCV Valve

Fortunately, it’s pretty easy to determine if your PCV valve or the valve hose has gone bad.

• You first need to locate the valve itself, which should be in a pretty accessible spot.
• When you’ve found the valve, remove it from the valve cover, disconnect the valve hose, and give the valve a little shake.

If the valve makes a rattling noise when you shake it, it’s probably working fine. The rattling sound you hear is the valve opening and shutting as your shake it. If you don’t hear any kind of sound, however, it means the valve is probably stuck.

You should also inspect the valve hose and look for any breaks in it. If you do find any, you’ll have to have the hose replaced.

As for the valve itself, depending on the condition it’s in you may be able to salvage it by cleaning it out. Otherwise, you’ll have to replace the valve.

When to Replace Your PCV Valve

In theory, the PCV valve should last more or less indefinitely, and will only need to be replaced if it actually breaks. However, it’s possible to restore a gunked-up valve to its original condition by cleaning it.

Cleaning the valve is actually pretty easy;

• Just get yourself some carburetor cleaner, pour some of it into a container, and let the valve soak in it for a while.
• The valve can be considered clean once it’s free of gunky deposits and if the valve’s color appears even. 

If this doesn’t work, you’ll have to swap out your old valve for a new one, but luckily this is also pretty easy. All you need to do is remove the old valve from the valve cover and disconnect it from its hose, install the new valve, and reconnect the hose.

How Much Does It Cost to Replace a PCV Valve?

Thankfully, replacing a bad PCV valve is one of the cheapest fixes to perform on a car. The part itself generally costs between $20-50, and if you do the fix yourself you can save the cost of labor.

Even if you’re buying the most expensive PCV valve possible and are having your car serviced at a costly repair shop, you shouldn’t expect to may more than $250 at the absolute maximum for a replacement PCV valve. 

Can I Still Drive With a Bad PCV Valve?

Technically you can, as a bad PCV valve doesn’t present any immediate safety issues, but we’d strongly recommend against it nonetheless. While you as the driver won’t be in any immediate danger from a bad PCV valve, your engine certainly will be. Driving for too long with a busted valve can cause all sorts of mechanical problems.

If your valve has indeed stopped working, you should have it fixed as soon as you can, unless you want to run the risk of having to fix significantly more expensive failures in the future.