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Understanding the PCV Valve: A Comprehensive Introduction for Car Owners

A PCV valve.

Your car's engine has several features that help it save fuel and run more efficiently. One of those features is the PCV valve.

The PCV valve is a small one-way valve attached to your engine block, usually on the top or side of the valve cover. It uses a vacuum hose to pull unburned fuel and exhaust gases from the engine crankcase back into the intake manifold.

The PCV valve is important to the health of your car's engine. But, unfortunately, a bad PCV valve can also cause problems.

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    A PCV valve.
    A PCV valve.

    PCV Valve Stand For

    PCV valve stands for Positive Crankcase Ventilation valve.

    Some vehicles have a CCV valve, which stands for Crankcase Ventilation valve. CCV valves are usually found in older cars.

    Even though these two valves have different names, they do the same thing.

    What Does A PCV Valve Do

    The positive crankcase ventilation valve function is to pull exhaust gases from the engine compartment to send them back to the intake manifold.

    The PCV valve was developed to help cars reduce toxic gases by recycling some of the exhaust back through the engine to ensure that it burns as much fuel as possible.

    This also helps with fuel efficiency, as well as offering some protection from the harsh conditions created by running the engine.

    When your engine burns air and fuel mixture during combustion, it creates a lot of pressure.

    This pressure can cause "blow-by," which is what it's called when some of the leftover exhaust gases are pushed past the piston rings of each cylinder.

    These gases get carried past the cylinder wall and into the crankcase.

    The crankcase is the bottom area of the engine, where the crankshaft, the oil pan, and the oil pump are located.

    The crankcase ventilation system uses the PCV valve and the natural vacuum created by the engine to pull the crankcase gases back into the intake manifold, mixed with fresh air-fuel mixture.

    This allows any unburned fuel to be adequately burned off instead of escaping through the exhaust system.

    This process also helps keep the crankcase's internal pressure regulated to a normal level.

    PCV Valve Location

    The PCV valve is almost always located on the top of the engine block.

    Most PCV valves will be mounted on top of the valve cover. It will be seated in a rubber grommet with a vacuum line attached to it.

    Some PCV valves may not be mounted on the valve cover but will usually be close to it. The intake manifold is another common location for the PCV valve.

    How Does A PCV Valve Work

    A PCV valve works by using a one-way valve attached to a vacuum hose.

    When you first crank your engine, it has no vacuum present, so the one-way valve stays closed. This allows your engine control unit to set the right air-fuel mixture for a smooth idle.

    As your engine runs, it creates a vacuum in the combustion chambers.

    This natural vacuum causes the one-way valve inside the PCV valve to open, drawing exhaust gases from the crankcase.

    What Happens If PCV Valve Is Disconnected

    It is easy to tell if the PCV valve gets disconnected. You will notice a few symptoms right when you start your engine.

    Your car will usually have a higher-than-normal idle, which may cause it to run roughly right when it first cranks.

    If you open your hood while your engine is running, you should hear a loud "sucking" sound from the engine bay. A vacuum leak causes this.

    This sound can be traced to the vacuum hose or vacuum port for the PCV valve, depending on where it's disconnected.

    What Happens When A PCV Valve Fails?

    You can tell if your PCV valve begins to fail in several ways.

    Problems with your engine idle, misfires, leaks, or increased oil consumption are all signs of a failing PCV valve.

    Bad PCV Valve Symptoms

    Since the PCV valve controls an integral part of your engine function, it can cause several problems if it goes bad.

    Here are a few things to watch out for if you think you may have a bad PCV valve.

    Oil Leaks

    The pressure that builds up in the crankcase when the engine is running has to have a place to go. It can force its way out through the gaskets and oil seals if it doesn't.

    This will cause your engine to leak oil. You will notice this oil leakage from a few common places.

    The oil pan gasket and the valve cover gasket are two of the most notorious places for these oil leaks.

    Contaminated Motor Oil

    A faulty PCV valve can cause contamination in your motor oil.

    The gases pushed into the oil pan contain exhaust and unburned fuel. Since they are under pressure and in contact with the oil, they can easily be absorbed into the oil.

    If you notice that your oil has a heavy gas smell or is beginning to turn into dark-colored sludge, this can signify a bad PCV valve.

    Rough Engine Idle

    The engine control unit adjusts the air-fuel mixture while the engine is running.

    If you have a faulty PCV valve or damaged PCV valve, this will throw off the mixture and can cause rough idling.

    Rough idling, engine stalling, and engine misfires can all be caused by a bad PCV valve.

    Check Engine Light

    The PCV valve can cause a check engine light to come on. In addition, several sensors can be affected by a damaged PCV valve.

    An engine misfire will almost always cause a check engine light. Likewise, misfires can happen when the PCV valve needs to be fixed.

    If the air-fuel mixture is incorrect, the oxygen sensor can get a bad reading. This will also cause a check engine light.

    If you have a check engine light that you can't figure out, then check the PCV valve. It could be the cause.

    Oil On The Air Filter

    Check the PCV valve if you notice oil stains on your car's air filter.

    A defective valve can allow excess engine oil to be drawn into your air intake. This will show up as oil being blown onto your vehicle air filter.

    PCV Valve Oil Consumption

    A faulty PCV valve can lead to oil consumption from your engine. Oil consumption occurs when your engine burns oil in the combustion chambers.

    An engine is supposed to have a small amount of oil on each cylinder wall for lubrication.

    However, if the crankcase pressure is too high because of a defective PCV valve, additional oil can be drawn past the piston rings and burned with the air-fuel mixture.

    This will show up in the form of blue smoke from your car's exhaust system.

    PCV Valve Stuck Open Symptoms

    A PCV valve can become clogged with deposits and get stuck open. This will cause a few different issues.

    The engine computer will read this as a vacuum leak and adjust your fuel mixture, which will cause your engine to run "lean" or with too much air and too little fuel.

    This will cause rough idling, hard starts, difficulty cranking, or engine misfires.

    It may also cause stalling or surging while driving since your computer will send the wrong fuel mixture to your intake manifold.

    How To Tell If PCV Valve Is Bad

    There are a few ways to test your PCV valve, but the easiest way to tell if the PCV valve is bad is to listen to the noise it makes.

    Remove the PCV valve from the valve cover with the engine turned off. It will probably be pretty dirty, so wipe it off.

    Shake it in your hand for a few seconds, and pay attention to the noise it makes (or if it makes any noise at all.)

    You can also test the PCV valve by disconnecting the vacuum line to see if it's working correctly.

    With the engine running, gently pull off the vacuum line that runs from the valve to the intake manifold at the manifold end.

    You should feel suction on the line when you touch your finger to the end of the vacuum line. This means that the one-way valve in the PCV valve is working as it should.

    If you don't feel any vacuum suction on the line, this is another sign that the PCV valve may be clogged or defective.

    Bad PCV Valve Sound

    A good working PCV valve will make a metallic rattling noise when you shake it.

    A bad PCV valve will make no noise at all.

    If your PCV valve doesn't rattle and is quiet when you shake it, there's a good chance it doesn't work anymore.

    How To Clean PCV Valve

    You can sometimes fix a clogged PCV valve by cleaning it. This may save you the trouble of having to buy a new one.

    Carburetor or throttle body cleaner are the best solvents to clean the PCV valve. You can use brake cleaner if available, but it can damage the PCV valve.

    Use rubber gloves and safety glasses when using solvents since they can harm you.

    Remove the PCV valve from the valve cover, and wipe it as clean as possible.

    If you don't have a lot of time and want to give it a quick clean, then you can spray it off with some cleaner and wipe it with a rag or paper towel.

    Be sure to let it air dry completely before reinstalling it. Spraying it with compressed air will help dry it if you have access to it.

    The best way to clean the PCV valve is to soak it in cleaner for a bit longer.

    Pour carburetor cleaner or throttle body cleaner into a small plastic container, and submerge the PCV valve in the cleaner. Let it soak for up to a few hours.

    Take the valve out and wipe it off until dry. Let it sit and completely air dry, or spray with compressed air before reinstalling it.

    PCV Valve Replacement Cost

    PCV valve replacement is usually not very expensive. The PCV valve costs around $10 to $15 at most auto parts stores.

    Since replacing the PCV valve is easy, you can do it yourself and save money.

    However, if you want to pay a mechanic to do the work for you, you would pay more labor costs than the cost of the part itself.

    You can expect to pay anywhere from $30 to $100 for a mechanic to replace the PCV valve.

    Since this is such an essential part of your car engine, the PCV valve replacement cost can be considered money well spent.


    Since the positive crankcase ventilation valve is a small part, it can often get overlooked when performing routine maintenance on your vehicle.

    This little valve is a big part of what makes your engine run correctly, so check it regularly.

    Taking care of it will help keep your engine running great and your car driving smoothly for years to come!