Bad PCV valve symptoms diagram

Bad PCV Valve: Most Common Symptoms And Fixes

Modern internal combustion engines are true engineering marvels. It’s very likely that in the future, we will look down at them as one of the most ingenious inventions of humankind. Despite the fact that internal combustion engines had humble beginnings, today, it’s one of the most complex pieces of equipment that we use every single day.

Apart from transforming heat into mechanical energy, modern engines have many secondary systems that take care of various things. These systems and parts weren’t initially used in ICE’s; however, their introduction made motors more reliable, durable, and efficient.

A great example of that is the PCV valve. At first glance, this is just a small component that many people think their vehicle can work without. And it absolutely can. Not that we recommend doing it, though. An engine without a PCV valve will quickly lose performance and efficiency. Oh, and that is just a few of the potential issues – other bad PCV valve symptoms are even more dangerous.

If you want to keep your car in perfect working condition, regularly inspecting the PCV valve and replacing it when required is essential. Luckily, replacing a PCV valve is not only easy, but it’s also cheap, especially if you do it yourself. You can even replace it as a precautionary measure and give your engine a little breathing room.

To give you a better understanding of the PCV valve, I’ll cover everything there is to know about this component. Apart from its role, I’ll point out all potential bad PCV valve issues, and how they affect your driving. Moreover, if you want to take your game to the next level, I’ll indicate how you can replace it yourself.

PCV Valve system

What is the Purpose of the “Positive Crankcase Ventilation” Valve?

For starters, PCV stands for “Positive Crankcase Ventilation” and the PCV valve is part of the EVAP system. I know, it’s hard to relate to this part only by its name. I had the same issue the first time I encountered bad PCV valve symptoms in my own car. Don’t worry, though – the PCV valve is a pretty simple part. What it does is significant, though – that’s why we even bother dedicating a whole article to it.

To better explain the purpose of the PCV valve, we need to start with the basics. And by basics, I mean burning fuel inside the combustion chamber. When an engine runs, every combustion creates gasses, which are then thrown out via the exhaust system. I suppose you already know that.

Now, the pistons inside a car engine have rings that should keep the same gasses from entering the crankcase. And, while they mostly succeed in doing that, a tiny amount of waste gasses will still pass through. More often than not, the fumes will contain unburned fuel. This can create all sorts of problems, which we will discuss further down below.

The “Positive Crankcase Ventilation” valve is designed to recapture the gasses using the engine’s vacuum. Or, as its name suggests, it ventilates the crankcase from the exhaust gasses that slipped past the piston rings. Dead simple, isn’t it?

Then, using a small hose, the PCV valve redirects the gasses into the intake manifold. By doing so, the engine can burn all the unburned fuel from previous strokes. This improves overall efficiency as most of the fuel is used to power the engine instead of being thrown out, unused.

Also, unburned fuel is much worse to the environment than burned one, so the PCV valve helps with emissions, too.

How Does A PCV Valve Work?

There are two PCV systems – open and closed. The former uses a vented oil filler cap to draw fresh air from the environment. This system was only used on older vehicles and can’t deal with larger amounts of gasses. In the case of excessive gasses in the crankcase, it will force them through the cap and into the atmosphere. Recent environmental regulations simply don’t allow that anymore.

Closed systems, on the other hand, draw air through the filter housing, and channels the crankcase gasses back to the intake manifold. Closed systems won’t let gasses escape into the atmosphere. Because of that, this system is very effective at limiting air pollution. For this reason, closed PCV systems are widely used in modern vehicles.

The PCV valve itself is very simple in its operation. The main purpose of the valve is to control the flow of vapors from the crankcase to the intake manifold. Usually, at lower engine speeds, the PCV valve stays closed due to a lower amount of gasses in the crankcase. At higher engine speeds, the PCV valve opens so it can quickly lower the pressure inside the crankcase.

To do all of these things, the PCV valve uses the vacuum from the intake manifold. When the vacuum is higher (lower engine revolutions), the valve is only slightly opened. When the vacuum is lower, for example, when the gas pedal is suddenly depressed, the valve opens up.

PCV valve diagram

Most Common Symptoms of a Bad PCV Valve

A bad PCV valve can cause many serious issues, especially if not taken care of on time. Here are the most common bad PCV valve symptoms:

  • Sludge can start to buildup in the crankcase, which can have serious repercussions on the engine in the long run (PCV valve clogged).
  • The pressure inside the engine will increase if the PCV valve doesn’t function properly. In some cases, this can damage vital parts, such as the piston rings and pistons, the engine head, the crankshaft, etc. (PCV valve clogged).
  • Due to increased pressure, oil seals and gaskets might fail, which will result in an oil leak in some places. Also, oil consumption will increase (PCV valve clogged).
  • Black smoke from the exhaust pipes might start to emerge.
  • Oil might emerge in the PCV valve or hose (PCV valve stuck open).
  • The engine will not work properly at idle and some misfiring might occur. Also, you might have trouble starting the engine (PCV valve stuck open).
  • Lean air-fuel mixture in case the PCV valve is stuck open.
  • The overall drop in performance and an increase in fuel consumption.

Can You Drive with a Bad PCV Valve?

Well, if driving means going forward, then yes, your vehicle will move with a bad PCV valve. However, my advice is: don’t do it, especially for prolonged periods. If the symptoms weren’t enough to convince you, know that if you don’t take care of the part soon, it can create a myriad of issues with the engine. Some of the issues might prove to be very costly, like a full engine rebuild.

How to Test A PCV Valve?

The Positive Crankcase Ventilation valve is probably one of the easiest components to test in a car. Since most valves are nothing more than a small metal ball inside a housing, to test it, simply remove it and shake it. If it’s clogged you would be able to hear the little ball moving inside. If it works fine, you should hear a slight “click-click” while shaking it.

Some other car models use a vacuum-operated diaphragm instead. In that case, you’ll need to use a vacuum pump to test it. Connect the vacuum pump to the control side of the valve and apply some vacuum. If it works fine, the valve should open when the vacuum is applied and close when it’s released.

How to Replace A PCV Valve?

Replacing the PCV valve is surprisingly easy. Moreover, the part is near the top of the motor, near the intake manifold or on the valve cover. If you aren’t sure how to proceed, I recommend getting your hands on your car’s repair manual. There, you will find the location and the manufacturer’s recommended procedure to replace the PCV valve. If you don’t have a repair manual at hand, just follow these general steps:

  • Locate the PCV valve in the engine bay.
  • Remove the clamp or the L-shaped housing that protects the PCV valve, and the hose connected to it.
  • Remove the valve. Depending on the model, you should either unscrew it or just pull it out.
  • Install the new valve into place and reconnect the hose.
  • Put the clamp back on over the PCV valve.
  • While replacing the PCV valve, it’s always good to check the hose. It should be clean on the inside and tough but elastic on the outside. Make sure it’s not cracked or the PCM might record a PCV valve or vacuum-related DTC code.

How Much Does It Cost to Replace a Bad PCV Valve?

Like with most car repairs, you’ll be paying more for labor than the part itself. Depending on the make, PCV valves cost from $15 to $30. However, if you decide to take your vehicle to the service, the labor alone will cost from $70 to $100.

Final Words

The PCV valve is another example of a seemingly insignificant part that can create many important issues down the road. In my experience, many car owners never touch this component, unless something goes wrong. And when that happens, the repairs are usually much more expensive than just replacing the bad PCV valve.

Fortunately, replacing this component is both straightforward and cheap. That should allow you to inspect and replace the PCV valve sooner and thus, prolong the engine’s lifespan. If you really care about your vehicle, you can do it every second or third oil change and avoid encountering any bad PCV valve symptoms.

By replacing the PCV valve at regular intervals, you will ensure that your engine always runs at its full potential. Also, it will save you from costly repairs down the line, and keep the resale value of your vehicle up. Maintenance is always better than a repair, especially in this case.

About Ivo G

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Hey guys and girls, I’m Ivo, a passionate car enthusiast with a particular weakness for rear-wheel-drive and stick-shift gearbox cars. Meanwhile, I don’t mind getting my hands dirty – I have experience as a Certified Head of Service at a Toyota Dealership, and knowledge that I wish to share with you.

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