The acronym PCV valve, which stands for positive crankcase ventilation, transfers excess gas from the crankcase to the PCV valve. From there, it goes to the intake manifold and down to the engine again.
Suppose the PCV valve hose breaks; there will be PCV oil consumption. That is to say, the gas will not go back into the engine, and the engine will experience a loss of power and have increased emissions.
In this article, we’ll discuss at length how you can test and replace your PCV valve and bad PCV valve symptoms. Before we move to that, Here’s this article in brief; what is a PCV valve? How does a PCV valve work? And how to tell if the PCV valve is bad.
What is a PCV valve?
PCV valve stands for Positive Crankcase Ventilation, and it is one of the oldest and most used emission devices in many vehicles.
The PCV valve’s function is to eliminate crankcase emissions from the crankcase and send them to the intake. The emissions are combusted again in another engine cycle, making the engine’s emissions cleaner and more efficient.
Most PCV valves are made the same way; two hosing connectors with a spring-loaded one-way valve inside.
When the engine is idle, you have a lot of vacuum inside the intake manifold, which helps the emissions get sucked out from the crankcase efficiently at lower speeds.
When you are revving up your engine and driving on higher RPMs, the PCV valve will open further and suck out even more crankcase ventilation caused by higher RPM and faster crankcase pressure build-up.
- Idle/Low RPM: High Vacuum, PCV Valve Half Closed
- Higher RPMs: Lower Vacuum, PCV Valve Open Fully
- Backfire from crankcase: PCV Valve Closing
If you have a turbocharged engine, you do not want to boost pressure to go into the crankcase, which would cause oil leaks and blow gaskets. Here, it’s crucial to have a one-way PCV valve.
These valves are designed differently, and the PCV valve only works on idle and low RPMs. Some PCV valves also have three connectors for a vacuum, which controls them with electric vacuum solenoids. These can work in a lot of ways, and we will discuss them in another article.
How does a PCV valve work?
The PCV valve is a one-way check valve that contains a spring-loaded plunger to regulate the flow of blowby gases. One end of the valve attaches to a hose connected to manifold vacuum, while the other end typically fits into the engine’s valve cover or intake valley.
When the engine is off, the PCV valve’s internal spring forces the plunger to close. But once the engine is running, manifold vacuum begins to pull the plunger open.
Then, the open PCV valve pulls fresh air, which enters the engine via a breather tube, through the crankcase. The resulting scavenging effect draws blowby gases into the PCV valve.
After leaving the valve, the gases enter a rubber hose that’s typically connected to the engine’s intake manifold or throttle body. The gases then enter the engine, where they’re burned as part of the normal combustion process.
The PCV valve cannot allow the same amount of blowby gases to enter the engine at all times, though. Instead, the valve must use its internal plunger to regulate flow, as follows:
- Blowby production is low when manifold vacuum is high. In this state, vacuum pulls the tapered-shaped plunger from its seat so that the gases can only flow through tiny grooves in the plunger’s body.
- As vacuum decreases and blowby increases, the plunger moves further away from its seat until it’s in a maximum flow position. Crankcase gases can then flow freely into the engine’s intake system.
But wait—that’s not all. The PCV valve also provides protection against backfires if necessary. If a backfire occurs in the intake manifold, the valve’s internal plunger will be forced towards the crankcase, preventing the flame from igniting fuel vapors inside.
PCV Valve Location
The PCV Valve is often located on the valve cover, on the top of the engine, but it can also be on a hose between the valve cover and the air intake filter.
Just follow the hose on the top of the car engine, and you will find the PCV valve. Some cars do also have an integrated PCV valve with the valve cover.
Bad PCV valve symptoms
The most common symptoms of a bad PCV valve include a rough idle, poor engine performance, and the Check Engine Light appearing on your dashboard. You might also notice increased oil consumption or blue smoke coming from the exhaust.
These bad PCV valve symptoms can lead to more serious engine problems if ignored, so it’s important to address them early.
#1. Check Engine Light.
One of the most common and most noticeable bad PCV valve symptoms is probably the check engine light on your dashboard. When the engine light shows up, there is a trouble code stored in the engine control module.
To read the trouble code from the engine control unit, you have to use an OBD2 scanner. Some older cars with a PCV valve fitted without an electronically controlled engine will not have this symptom.
#2. High Idle RPM/Rough Idle.
Because the PCV valve controls the airflow between the crankcase and the intake manifold, a broken PCV valve can have the same symptoms as an intake air leak.
Which can cause the idle RPM to get too high and other strange idle behaviors like a very rough idle. If you have any strange idle problems, it’s always a good idea to check the PCV valve first.
#3. Lean/Rich Mixture.
Because of the issues discussed, a faulty PCV valve can have the same symptoms as an intake leak, and the air/fuel mixture can end up being wrong. Usually, your air/fuel mixture will become lean, and you can feel the same symptoms as from a lean mixture.
With a rich mixture, you can often see that the car has a little more gray/white smoke than usual, and you can often detect the smell of petrol. Lean mixture is more difficult to find, but it often causes misfires, as we will discuss next.
#4. Misfires.
Because you can get a faulty lean/rich mixture due to a faulty PCV valve, you might feel misfires while idling or accelerating when your PCV valve is bad.
If you have a too lean mixture, the cylinders won’t fire up correctly, which can cause misfires. If you have a mixture that is too rich, you can turn off the spark with the fuel and therefore cause a misfire.
#5. Rough Acceleration.
When you have a faulty PCV valve causing a wrong fuel mixture, you can feel that your car has rough acceleration on high and low RPMs.
On most cars, you won’t feel a broken PCV valve on higher RPMs than idle, but it’s worth mentioning because it can happen depending on the valve’s design.
#6. Increased Oil Consumption & Oil leaks.
If the PCV valve or the hoses are blocked by moisture, you will get a very high pressure inside the engine crankcase, which will push the pressure up in the cylinders and out from the gaskets.
If you suddenly see several large oil leaks and increased oil consumption in your car, check the PCV valve and the hoses to it to make sure they’re not blocked.
#7. White/Black/Blue Smoke from the Exhaust.
If the PCV valve or the hoses are blocked, the crankcase will push oil up into the combustion chambers, which will cause oil to burn inside the engine and go out through the exhaust pipe.
This will cause a lot of blue smoke from the exhaust pipe. If the PCV valve is faulty and causing a rich or lean mixture to the engine, you can get symptoms like white or black smoke coming out from the exhaust pipe, depending on what type of mixture problem the engine has.
A short conclusion is: If you see any strange smoke from the exhaust pipe, make sure that the PCV valve is in good shape.
How do you test and replace a PCV valve?
Many vehicle manufacturers have different component replacement and maintenance intervals. PCV system service is no exception. However, some manufacturers suggest servicing them every 20,000 miles.
In general, you should carry out a PCV valve test and servicing every 20k to 50k miles. In any case, earlier and more frequent inspection and maintenance help to keep your engine running nice and smoothly.
So, to start PCV valve inspection in your car, first, you need to find the valve location in your vehicle.
The PCV valve location varies contingent on your car’s make and model. 90% of the PCV valve in automotive engines are found on the valve cover, while on some other vehicles, they are found on a breather hole on the intake manifold.
If you can’t locate the PCV valve on your vehicle, you can purchase a service repair booklet for your car model from any nearby auto store.
#1. PCV valve flow operating testing.
- Inspect the PCV system components. Pcv rubber grommet, O-ring, and hoses and see if they have turned hard and become brittle or swell due to exposure to harsh engine conditions. Replace any faulty components if need be.
- Gently take off the PCV valve and the hose, visually check them, see if there is any slime on the PCV valve and the hose, clean the hose with cleaning solvent or WD 40, and change the PCV valve. You may have to replace the related component and the valve itself.
- Most vehicles use a cheap and simple valve under $6, and car owners should replace the valves on every major service interval. In contrast, other luxurious cars use PCV valves incorporated with heating chips and are costlier. Whether or not your engine uses the PCV valve with heating chips, always get a high-end valve.
- Some engines have a filter on the PCV valve. Some manufacturers recommend changing the filter every 30k miles.
#2. Testing PCV for vacuum.
- Turn on the engine and run on idle for some minutes until the engine gets to its average temperature.
- Locate the PCV valve and disconnect it from the engine while leaving the hose attached to the valve; then, cover the other side of the valve with your finger.
- You’ll feel a vacuum sucking at your fingertip, the engine speed should drop by about 40 – 80-RPM.
- If the rpm drop is more than 40 to 80, and the engine idles roughly, chances are you have a stuck open PCV valve.
- If you don’t feel suction at your fingertip, inspect the valve and the hoses and see if they’re clogged.
- Suppose you find any damaged hose or defective valve, go ahead and replace them.
#3. Other alternative PCV valve testing methods.
- An alternative way to check the PCV valve is to block or pinch the valve hose. The engine speed should drop by about 40-80 rpm, and then the hoses go back to normal. If it doesn’t work this way, look for a clogged or blocked PCV valve or damaged vacuum hose.
- The PCV valve may be located in a hidden spot on some vehicles. On such an engine model, instead of going long process of losing many other engine components, take off the motor oil dipstick, get a masking tape and cover the dipstick opening tube.
- While the engine runs on idle, locate and take off the engine oil filler cap. Then, cover the opening with thin cardboard.
- Stay back and allow the engine to idle for one to two minutes. You should notice a suction pressure dragging the masking tape against the dipstick hole. Otherwise, you have a clogged PCV system or a vacuum leak. Check for the hose’s conditions, the rubber grommet, and the valve itself.
In a situation you have a clogged PCV valve, damaged hose, or defective grommet, simply take it off and replace it with a new quality one. PCV valves and their connections are some of the cheapest components in your vehicle; as such, you need to go for a high-end one.
How to replace PCV valve?
PCV valve replacement is a simple and cost-effective maintenance task. Follow these steps:
- Locate the PCV valve: It’s usually found on the valve cover or near the intake manifold connected to a vacuum hose.
- Remove the old PCV valve: Carefully detach the vacuum hose from the PCV valve. If it’s a push-in type, pull it out of the grommet. If it’s threaded, use a wrench to unscrew it.
- Inspect the hose and grommet: Check for cracks, leaks, or wear on the hose and rubber grommet. If damaged, replace them.
- Install the new PCV valve: Insert the new valve into the grommet or screw it in place. Ensure it’s secure but not over-tightened.
- Reconnect the vacuum hose: Attach it back to the valve, ensuring it’s adequately fitted and leak-free.
- Start the engine and check for leaks: Let the engine idle and listen for unusual noises. Check for vacuum leaks or performance issues.
How much should it cost to replace a PCV valve?
Several factors can affect PCV valve replacement cost – factors like the PCV valve location, the garage you service your vehicle, and your car model.
In any case, the average replacement cost of a PCV valve should be around $25 to $50. The part price should be $5 to $10, while the service charge will be $20 to $40.
FAQs.
Q: How long can I drive with a bad PCV valve?
The positive crankcase ventilation (PCV) valve is cheap, so you shouldn’t ignore changing it at recommended intervals – around 30k – 50k miles.
It’s never recommended to drive long with a defective PCV valve. Driving up to 10hrs with a lousy PCV valve could be very risky.
Q: Can I use WD-40 to clean the PCV valve?
Yes, you can clean the PCV valve with WD-40. All you need to do is, disconnect the PCV valve from the rubber grommet on the valve cover or intake manifold and spray WD-40 on the valve and allow it to penetrate in to dissolve the dirt and debris inside.
And flush it out with WD-40. However, I do not recommend cleaning a clogged PCV valve – you can get a high-end valve for under $10.
Q: Will a bad PCV valve burn oil?
Due to the high pressure in your engine, a defective PCV valve can cause engine oil leaks from serious engine seals resulting in excessive oil consumption and oil puddles on your vehicle.
Ensure you inspect or contact a professional mechanic to inspect and replace the lousy PCV valve.
Q: How often should a PCV valve last?
There are no replacement intervals for PCV valves. PCV valves should last as long as they should. Ideally, you should inspect your PCV valve on every major maintenance.
Or, you can replace it every 30,000, 60,000, or 90,000 miles, depending on the result of your test and how it looks.
Final word
Most times, bad PCV valve symptoms show up in the form of bad sensors. This is why it is imperative to check your PCV valve and other related components regularly.
Finally, most PCV valves and their related components are worth $5 to $10, so it pays to regularly check and replace them to avoid costly repairs that might even damage your engine.