While it’s true that not every car repair is beginner-friendly, wrenching on your car isn’t something you have to fear. Even inexperienced home mechanics can perform basic maintenance tasks like changing the oil or replacing the brake pads, for example. Plus, some of these tasks, such as cleaning out a throttle body, are easier than you might think. And that includes replacing a bad PCV valve.
What does a PCV valve do?
An internal-combustion engine relies on a lot of different valves to run properly, efficiently, and (relatively) cleanly. For one, it wouldn’t work at all without intake and exhaust valves controlling the airflow. Also, it would emit far more NOx gases if not for the EGR valve. And your car’s engine would be far dirtier and less efficient if not for the PCV valve.
‘PCV’ stands for ‘positive crankcase ventilation,’ and that’s what this valve regulates. Normally during the combustion process, the engine’s pistons push waste gases out of the exhaust. But sometimes, they pull air, unburned fuel, and waste gases into the crankcase below instead. Technically, piston rings are supposed to prevent this, but neither they nor the valve guides are 100% foolproof, CarBibles notes.
However, this ‘blow-by’ isn’t merely a minor exhaust annoyance. The mix of fuel and waste gases can contaminate the engine oil your crankcase holds. This causes sludge, which clogs up your engine and in turn causes corrosion. Also, pressurizing the crankcase can damage seals and gaskets, creating further issues.
Originally, automakers just vented these crankcase gases away. But because blow-by contains unburned fuel, it meant a lot of emissions—more than any catalytic converter can deal with. Not to mention the fact that you’re wasting fuel.
That brings us to the PCV system and the PCV valve. An inlet hose brings filtered fresh air into the engine to pick up the dirty vapors, CarBibles explains. These vapors exit via the PCV valve, which has a spring-actuated plunger inside. This plunger is a one-way device that sends the gases back into the intake and combustion chamber via another hose. There, the vapors are combusted, which reduces emissions and improves fuel economy, Autoblog explains.
Is it the same thing as an oil separator or catch can?
The PCV system and PCV valve have other duties, though. For one, as your engine heats and cools, moisture can condense into the oil. And getting water into your oil can do far more than cause corrosion. Venting the heated gases off, though, mitigates this, CarBibles says.
Secondly, as the crankshaft in the crankcase spins, it often churns the oil below. And if blow-by gases can get into the crankcase, then these oil vapors can get out. This can lead to oil coating your intake and exhaust and even backfires. The PCV system and one-way valve prevent this by drawing these vapors off and regulating air pressures.
To some, this might sound like an oil catch can or oil separator. And in some cars, including my Fiat 500 Abarth, the PCV valve is built into the oil separator, which causes further confusion. However, although oil catch cans are part of the PCV system, they are not PCV valves. The latter regulate air pressure to help vent oil, waste gases, and fuel, while the former physically filter out oil from airstreams.
But using an oil catch can or oil separator can keep a PCV valve cleaner for longer. And as we’re about to explain, that’s important for valve longevity.
What are the signs of a bad PCV valve?
Although your PCV system prevents certain causes of sludge, all engine oil eventually gets dirty over time. And this dirty oil, as well as moisture and inevitable wear and tear, can cause your PCV valve to stick and/or clog. Only driving your car short distances without letting the oil get up to temperature properly can accelerate this valve failure, CarBibles warns.
Luckily, there are several signs that your PCV valve might need replacement. You might hear it ticking, or perhaps whistling, whining, or groaning. A stuck-open valve often causes a Check Engine Light, Autoblog says, as well rough running and even backfiring. And if the PCV valve fails because of sludge buildup, it often causes excessive oil consumption.
There are also some visual signs of PCV valve failure. Oil spots/leaks by the PCV inlet hose or on the air filter element point to valve failure. Also, as noted earlier, the PCV system helps regulate pressure to prevent seal failure. So, if a minor oil leak suddenly becomes worse, you’ve likely got a bad PCV valve. And if the valve has failed, subsequent gasket failures often cause milky or cloudy oil due to fluid contamination.
If you’re experiencing any of these signs, there’s a simple way to check if the PCV valve is the problem. Remove it from the engine and shake it. If it doesn’t rattle, then the springs and plunger have failed, which means you need a new valve.
You don’t need to wait for a mechanic to replace a PCV valve
Fortunately, if you catch valve failure early, you can avoid the worse complications. And for most cars, PCV valve replacement literally takes a few minutes. It’s also cheap: most replacement valves cost less than $10, and some even less than that.
First, locate your PCV valve, which has a straight or bent nozzle at one end. In my old 1999 Miata, for example, the valve was out in the open on the valve cover, as shown in the picture above. Meanwhile, as I noted earlier, my 500 Abarth’s valve is attached to its air-oil separator, which required removing the engine cover to access.
Regardless of your car, though, you’ll have to detach at least one PCV hose to get at the valve. Then, simply remove the old valve and install the new one. Reattach the hose(s) and you’re done.
It’s worth noting that PCV hoses can also clog over time and need replacing, Autoblog reports. Fortunately, that process isn’t any trickier than replacing the valve itself, though you may have to remove your engine cover. In addition, if your car has an oil separator, that needs to be cleaned out regularly, too. So, if you’re replacing the PCV valve, clean the separator out while you’re at it.
Still, when it comes to DIY car maintenance, PCV valve replacement is a walk in the park.
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