What Does A PCV Valve Do

What Does A PCV Valve Do: Why Does Your Car Need One?

by Taufiq Haque

Mechanics and professionals often throw around specific terms and phrases if you have a car. Some of them might have been “PCV valve” or “crankcase.” And, if you do not know what they mean when they say this, you have come to the right place.

You will grow interested in PVC valves and crankcases as a vehicle owner. Because changing the PVC valve located in the crankcase, is a part of regular maintenance that a car needs. Knowing how to change PVC valves will save you a few trips to repair shops and make your life easier!

But what is a crankcase? A PCV valve? And, what does a PCV valve do? These are some basic questions that might arise in your mind. So, without further ado, let’s learn everything that has to do with PVC valves!

What Is A Crankcase

Before we start with a PCV valve and its workings, let’s learn what a crankcase is. You can think of the crankcase as the central component of an engine. It holds all the crank mechanisms, including the cylinders, connecting rods, pistons, gearbox or transmission, and the engine control system.

The crankcase, or engine block, is considered one of the most complex car parts in combustion engines. Because it requires designing lubrication and cooling channels down to a T. So, manufacturers must build and test it through CAD systems first to achieve this precise design.

Manufacturers build the crankcase through casting technology once the dimensions are accurate. Also, the bearing blocks are placed perfectly through the CAD systems. They use iron, carbon, silicon, manganese, and phosphorus to create these cavity-free castings. They make molds for the internal shape of the crankcase, and the materials are used in precise quantities for quality.

So, now that you know about the crankcase, you might be wondering what a PCV valve does in the crankcase. Keep reading below to learn more!

What Is A PCV Valve

Before we get into what a PCV valve does in the crankcase, let us discuss what a PCV valve is.

A PCV valve, or positive crankcase ventilation, is a component that allows airflow within the crankcase. Remember how we previously mentioned that the crankcase requires cooling channels?

Well, the PCV valve is just that. It allows air into the crankcase and lets harmful oil vapors escape it. The valve prevents the numerous gaskets and seals within the engine from damaging and boosts its performance. Not only that, but it also helps the environment! Without the emission of harmful gases, it allows automobile emission control and keeps the environment clean.

Where Is The PCV Valve Located

Replace the PCV valves regularly. Why? You might ask. It is because the release of engine vapors often ruins them. Hence, you should know where these valves are located so that you can save a few trips to the mechanic.

The PCV valve location is relatively easy to find. It is usually located close to or inside the valve cover within the crankcase.

Typically, the PCV valve’s shape is L. It regulates the crankcase’s vacuum application amount, and the valve opens and closes to increase or decrease the airflow.

What Does A PCV Valve Do

Although small, a PVC valve undoubtedly has one of the most crucial jobs. It is why you must ensure it does not damage or wear out. And to do so, you must keep maintaining it and replacing it from time to time.

But what does a PCV valve do? To understand that, you will need to first understand how the internal combustion engines of cars work.

How Does The Internal Combustion Engine Work

So, the internal combustion engines of cars, which are crankcase insulations, have a very mechanical movement. Now you know what crankcases are and have watched a demonstration of how they work. So, this should be easy for you to grasp this part.

If you look at the PCV valve diagram, i.e., how the internal combustion engines are composed, they have hollow cylinders. These cylinders are arranged in a series and have pistons that move up and down inside them.

The engines also have “intake manifolds,” tubes that carry a mixture of air and gasoline. When this mixture travels to the cylinders’ intake valves, sparks from the car’s spark plug cause this mixture to explode. The explosion occurs in the open space between the cylinders and the pistons and is called the combustion chamber.

What Does A PCV Valve Do

The explosion created causes the pistons to repel downwards into the cylinder, and this causes the crankshaft to rotate. The crankshaft then turns the car’s gears, thus pushing it forward.

There is another thing that simultaneously occurs as a result of the explosion. It causes the piston to push upwards again. Then, it redoes this entire process and forces the excess gas out through the cylinder and exhaust valve. However, not all of the air and gas manage to escape.

A small amount of the excess air and gas slips through the piston rings and makes its way into the crankcase. The amount is called the blow-by, which brings the PCV valve into action.

How Does A PCV Valve Work

It is finally time to answer the question you have been waiting for: what does a PCV valve do?

So, the main task that the PCV does is that it recycles the blow-by gas and keep them out of the crankcase. Since the blow-by gas can ruin unburned gasoline in the car and lead to problems within the crankcase.

But this did not always exist. Before the PCV was invented in the early 1960s, the blow-by air in the crankcase was allowed to circulate freely. It was released as emissions on the environment, which was highly harmful.

Hence, following the invention of PCV valves, the blow-by air was pumped back into the cylinder to repeat the combustion process. But this repetition had its complications too. Since the blow-by air was mainly air, the mixture of air and gasoline in the combustion chamber was too lean. It prevented the combustions from being as effective and thus led to a different method.

The blow-by mixture was only recycled when the car traveled at a low speed. It made combustion more effective. Why? Because the engine at idle resulted in the air pressure in the intake manifolds being lower than the crankcase. The lower pressure causes the blow-by gases to be sucked out through the PCV valve right back into the intake.

However, the air pressure in the intake manifold increases when the engine is up to speed. Thus, it reduces the number of recycled blow-by gases in the crankcase. The purpose of PCV valves is to keep blow-by gases out of the crankcase. The valve closes off when the excessive pressure in the intake manifold tries to force itself back into the crankcase.

Bad PCV Valve Symptoms

The PCV valve has a taxing job to do. Even after keeping the blow-by gases out of the crankcase, it has to redirect the gases to the exhaust system. The catalytic converter transforms these gases into their less-toxic version, which is emitted from the tailpipe.

These emissions need to be extremely clean before they are in the environment. A necessary component you will need to ensure this is a PCV valve. However, PCV valves do not last very long; they go wrong after being used for a few years.

Luckily, the PCV valves show signs when they are going bad, and you can recognize the symptoms simply by keeping an eye out for them. Some of the common bad PCV valve symptoms include:

1. Oil Leakage

What Does A PCV Valve Do

Oil leakage is the most definite symptom of the PCV valve going bad. It can be caused when the valve is clogged or worn out. If the PCV valve is worn out, it is stuck in a closed position, causing it to be blocked.

Thus, your main plan should be to find a PCV valve replacement as soon as possible. The pressure in the crankcase will build up, causing an oil leak.

Since you already know what a PCV valve does, you know how important it is that the valve remains functional. So, if you think the valve is at the end of its life, check your seals and gaskets. It would be best to look for them in your intake manifold, exhaust valves, or your throttle body.

If all else remains unfruitful, check the air filter, and do not forget to look at the floors for oil splatters. If your PCV valve is not functioning well, you will find oil near or within your car’s vicinity.

2. Stalling Engine

Just as an oil leak can occur if your valve is closed shut, the engine can stall if the valve is open.

An open PCV valve can let excessive amounts of air into the combustion cylinders and chambers, making the air-gasoline lean. This lean mixture, caused by too much airflow, can result in the engine stalling.

3. Sludge Build Up

The sludge build-up is a silent killer. Because you will not see it unless you inspect your engine and look for it. Thus, it will completely ruin your engine over time, and you will not even notice!

The sludge you will see is a residue left by the leak of gases from the combustion process into the engine oil. This sludge residue builds up over time until it covers the engine and damages it entirely.

4. Poor Fuel Economy

Keep an eye on your PCV valve oil consumption. If you notice that your car is being depleted of your fuel quickly, your PCV valve is likely closed. If that’s the case, there’s a possibility that your filled cylinders are a rich mix of gasoline and air.

Since this will lower your fuel economy. Not only will you be spending more on gas, but it will emit toxins, making you fail the emission test.

5. Engine Light

When a PCV valve gets ruined, there is likely too much gasoline or air in the combustion chamber. An easy way to detect if this is the case with your car is to check the warning lights.

The car sensors will relay the air-fuel mixture status during the combustion process to the engine control unit. It will then turn the warning lights on if there is something wrong. You should check your car with an OBD-II scanner for fault codes.

You will get codes like P053A or P052E, which are specific to the PCV valve. Otherwise, you might also get codes like P0171 or P0174, which are much more common.

6. Engine Smoke

What Does A PCV Valve Do

Sometimes, it gets stuck while it’s open; other times, a system hose ends up ruptured or disconnected. It usually causes a vacuum leak, leading to the engine emitting black smoke. That is the tell-tale sign of a damaged PCV valve.

7. Bad PCV Valve Sound

The combustion chambers, vacuum hoses, and gaskets are prone to dust and debris accumulation. It can cause your PCV valve to be making sounds. Sometimes when the residual sludge accumulates for a while, you might also hear sounds from the engine.

If you notice this happening, inspect the valve immediately. Ignoring it could lead to more significant issues that could damage your entire engine.

How To Test Your PCV Valve

Testing to see if it’s still functioning is quite simple. There is only one way to check if the valve needs to be replaced.

You have to test the PCV valve by removing it from the tube or hose and shaking it. If you hear a rattling noise, it is working well. A clogged valve doesn’t make any rattling noise.

You could try cleaning it to see if it works, and you might even get lucky and have it function again. But, in most cases, the PCV test reveals that they are required to be replaced.

How To Clean The PCV Valve

If you do not want to replace your PCV valve and want to salvage it by cleaning it. Here is a step-by-step instruction on how to clean it:

  • Check your repair manual and find the PCV valve; it should look like a cylinder that is located at the top of the crankcase
  • Carefully take off the thick rubber hose attached to the valve
  • Wrap the valve with a rag and clamp it with pliers; pull on it to remove the valve from the engine
  • Remove dust and debris from the hole by using compressed air
  • Spray it with an engine degreaser to make sure it does not clog back up
  • Push the PCV valve onto its original location again and attach the hose to it

PCV Valve Replacement

Replacing it is just as easy as cleaning it. Even though many people go to a mechanic to replace theirs, you can easily do it yourself. Here are the steps for replacing your PCV valve.

  • Check your repair manual and find the PCV valve; it should look like a cylinder at the top of the crankcase.
  • The valve is attached to a thick rubber hose; take it off carefully
  • Wrap the valve with a rag and clamp it with pliers; pull on it to remove the valve from the engine.
  • Take the new one and place it in place of the previous one.
  • Attach the hose back to it

And there you have it! Was that not easy?

What if we told you there was an even simpler solution to this? You could avoid changing the PCV valve often if you get a PCV delete; it will make your life easier.

PCV Delete

As opposed to a PCV valve, the PCV delete just ventilates it. So, you need to change PCV valves because they build up dirt from recirculating the engine’s gasoline, air, and oils.

Compared to that, the PCV delete has a PCV filter that purifies the mixture and emits it. You will not have to worry about the valve clogging and damaging your engine with a delete! And, the best part is, installing it is just as easy. Here is how you do it:

  • Check your repair manual and find the PCV valve; it should look like a cylinder at the top of the crankcase.
  • A thick rubber hose is attached to the valve; take it off carefully
  • Wrap the valve with a rag and clamp it with pliers; pull on it to remove the valve from the engine
  • Take the PCV delete and place it in place of the previous one
  • Attach the hose back to it

PCV Valve Oil Consumption

A bad PCV valve can consume oil and leave you with poor fuel economy within a few hours. The oil leaks can even cost you the loss of 10% of the total amount if you do not notice it soon enough!

Also, without proper ventilation, the engine can suck in oil which can accumulate in the crankcase and cause sludge to cover the entire machine. Hence, you must check your PVC valve as often as possible.

PCV Valve Replacement Cost

Since PCV valves are reasonably easy to repair, the overall cost will depend on whether you can replace them yourself or not.

Generally, the PCV valve replacement cost can be between $35 to $75 at repair shops. However, only the money $10 to $15 is the valve’s actual cost. So, if you learn to change it yourself, you can save up to $60 on it!

Since PCV valves are something, you will need to replace often, it is best if you learn to do it yourself! It might look tricky, but try to follow the steps carefully.


What does a PCV valve do? If you have a car, you have undoubtedly heard of it and wondered what it does. We hope this article has taught you everything you wanted to know and more.

So, what are you waiting for? If your car needs a replacement, do it immediately! At last, we arrived at the end. How was it? Did you find the answers you’re looking for? If so, we are glad to help! So, take care of yourself and check your cars properly!


What Does PCV Stand For

PCV stands for positive crankcase ventilation. It recirculates the positive pressure back into the intake.

What Is A PCV Valve On A Car

This is a component of the car’s engine. A crankcase encases the engine, which is prone to a stuck mixture of gas and air. If this mixture collects over time, it will damage the engine. Hence, the PCV valve redirects the mixture and recycles it or emits it through ventilation to prevent that.

Do You Need Positive Crankcase Ventilation

Yes, it would help if you had positive crankcase ventilation (PCV valve) for a few reasons. Firstly, it prevents drawing excessive oil proportions out of the crankcase. Secondly, it regulates the air pressure of the vacuum the crankcase applies regularly and prevents any overpressure from taking place. Lastly, it can act as a way to check whether the valves you have are experiencing a forced induction or a misfire. Thus, it’s better to have a PCV valve.

Can A Bad Purge Valve Cause Misfire

Yes! Since the PCV valve allows the air-gasoline mixture to be emitted through the EVAP, a lousy purge valve can cause a misfire. If the valve is defective and refuses to open or close, the recyclable gas will continue to connect, thus misfiring.

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