Table of Contents
What is the PCV Valve?
PCV stands for Positive Crankcase Ventilation. The PCV system is an integral part of your engine. It removes vapors that are harmful to it and prevents them from entering the atmosphere.
The PCV valve is used to control the flow of these harmful oil vapors from the crankcase to the intake manifold. Although it might not be something you’ve thought about – or even heard about – before, it’s an item that should be replaced with every full service. While these valves don’t necessarily have an expected lifespan, it’s important to make sure yours is always working.
What is the PCV System?
Most engines run using a 4-stroke stroke system: suck, squeeze, bang, blow. In technical terms, these phases are called intake, compression, power, exhaust.
In the intake phase, air and fuel are sucked into the cylinder as the piston lowers. After this, the piston begins to rise again and compresses the air and fuel mixture. Just before the piston reaches TDC (Top Dead Centre), the spark plug creates a spark, igniting the air and fuel mixture, causing the power stroke. Power strokes technically power your engine. After this, the piston rises again. The exhaust valve opens, squeezing the leftover gases out of the cylinder in preparation to start the cycle again.
During the power stroke, a minimal amount of vapors manages to get past the pistons and piston rings, collecting as vapors in the crankcase. These are called blow-by gases. It’s important to remove these as soon as possible. They’re harmful to both the engine and the environment.
This is where the PCV system comes in. Air is pumped in from the intake manifold. There is another hose – the vent hose – leading from the crankcase back to the intake manifold, and these are often on opposite sides of the engine. The PCV valve is located in the vent hose, going from the crankcase back to the intake manifold.
The air that’s pumped in creates a vacuum in the vent hose leading back to the intake manifold. This results in the vapors collecting in the crankcase being sucked out and going back into the intake manifold. From here, they go through the engine again and get burnt.
This cycle repeats all the time that your engine is running. The PCV valve regulates how much of the fuel vapors leave the crankcase and goes back into the intake manifold. You will usually find the PCV valve on the valve cover – sometimes it will be on or around the intake manifold or throttle body.
Symptoms of a Bad PCV Valve
You might see black smoke from the exhaust. This is because the fuel mixture becomes richer if the valve gets stuck open. A higher ratio of fuel is injected into the cylinder in comparison to the air it’s mixed with, resulting in black smoke pouring out the rear of the car. This could also be caused by many other things such as faulty fuel injectors, a partially blocked air intake system, and more, so watch out for that.
You might notice an oil leak. These are caused by excessive pressure from a clogged valve. Often leaks form at gaskets and seals in the oil system. You will probably notice a small oil puddle under the car when it has been stationary for a while. The excess pressure in the system could also lead to a higher rate of oil consumption than is normal for your vehicle. If you have an oil leak, don’t forget to check your oil level once you’ve fixed it, potentially topping it up or draining it and putting a new load in.
When you change the oil, you may notice a lot of sludge in it – it won’t flow naturally very easily. If you notice this, the blow-by gases (fuel vapors) aren’t being removed from the crankcase. They are often the cause of this “sludge.” The most likely cause of this is a faulty PCV valve, although it could be one or two other things. In this case, you will need to replace the oil after having diagnosed and fixed the problem. Check the condition of your oil filter as well. If poor-quality oil has been thrown through it for a while now, you may need to replace that too.
The engine will be running roughly, potentially including misfires, a lack of power, and a rough idle. Your check engine light may also come on. When a code reader is attached to your car, the ECU can often make a mistake and display codes saying there is a problem with the MAF (Mass Air Flow) sensor or lambda (oxygen) sensor. Bear in mind that this could be the problem when your check engine light comes on.
In some engines, the PCV valve is located near to the air filter. If you notice oil spots on the air filter element, this could be because the valve is stuck open, allowing droplets of oil through the system.
How to Test Your PCV Valve
To see if your PCV valve is the problem with your car, you need to locate it. On most cars, you’ll find it somewhere around the valve cover or the intake manifold.
When you have removed the vent hose attached to it, remove the valve. Give it a shake a listen for the valve moving around. It’ll be a kind of rattling sound. If you don’t hear anything, it’s not working, and you need to replace it.
If the valve is working, there could still be a problem somewhere in your PCV system. You should inspect all the rubber parts you can, including removing the hoses and looking closely at them for any potential vacuum leaks.
Remember that the PCV system works on the principle of a vacuum, so anything that compromises this could cause the whole system to be faulty.
How to Change Your PCV Valve
You can change the PCV valve yourself at home. It’s a relatively simple procedure, with slight variations from car to car. Make sure you look up how to do it on your specific model before beginning the work. Good places to look for this include YouTube, Haynes Manuals, and asking your local mechanics how to do it.
To change your PCV valve, first, get yourself a new one. You should be able to get one of these from most part stores, depending on how common your vehicle is.
With your hood open and the engine off, disconnect the vent hose and remove the valve by twisting it counter-clockwise. Then, it’s very simple. Just replace it with the new valve, putting it back in the same way, and reconnect the vent hose.
That’s all there is to it.
Problems with the PCV system can be particularly difficult to diagnose if they aren’t to do with the valve. If you think there might be a problem somewhere else but aren’t sure what it is, take it to a garage and get the mechanics to look at it for you. You may need some more specialist help if it reaches that stage.
If there’s a problem with the PCV valve alone, you shouldn’t have much difficulty fixing it yourself. By automotive standards, it’s one of the easiest jobs you can do.
Keeping on top of the PCV valve’s condition means that you’ll ensure your engine is working in top-notch condition, keeping you safe and saving you money. Make sure your knowledge is up to date with what the symptoms of a failing PCV valve are to make sure you can get it fixed as soon as possible.
We hope this article has been useful and will help you diagnose the fault with your car.