Ditch That PCV System Before It Is Too Late

Yes, PCV, not PVC. Positive Crankcase Ventilation. Does your car have this “system”? Yes, more than likely; unless you are Orlove and drive an antique. Let me clarify something here. Positive crankcase ventilation is a requirement for almost every gas powered combustion engine found in cars. But how its utilized in modern days is what could be harming your engine.

In case you are unaware, when an engine is running and the piston is forced downward from the combustion process an unavoidable amount of air/fuel/gases makes it past the piston rings which “seal” the cylinder chamber. This mix of air/fuel/gases is a result of the pressure created from the combustion/explosion. It gets forced into the crankcase. This is called blow-by. To combat this pressure inside the crankcase, they developed a vent for it to vent out the pressure or keep a even pressure inside the crankcase.

With me so far? Great! So this is all fine and dandy, really. Except one thing. Inside the crankcase lives lots and lots of motor oil. So, all of this blow-by forced into the crankcase gets vented and along with it comes oil. In the early days, they used what was called a draft tube. Basically it was a tube that attached to the motor where this vent was, and it ran down to the bottom of the engine bay under the car. The draft of air under the car while you were driving whisked away the oil from the tube and straight under the car on to the road.


Eventually we figured out that this all was not the most environmentally friendly or efficient way to go about dealing with blow-by gases. So “we” developed a new way to process this pressure and escaped oil. And what ingenious technological advancement was that? Feed it right back into the motor!

Alright, that sort of makes sense. Keep the gases and oil inside the motor where they belong. Well, once you realize WHERE it feeds back in is where it starts to make less sense. It just so happens that that majority of the time this goes directly into your intake track, intake manifold, or throttle body. Often one side of the system is connected via a small hose to the air intake tube which helps put the system into a vacuum. The other side of the system has a one-way valve which lets pressure escape where it is then fed into your intake.

Whats the problem with that you might ask? Well, you are blowing motor oil into your intake system. Simple as that. Depending on your car and where it feeds back in, it can gunk up your throttle body, your intake tube and resonator, your entire intake manifold, etc. And no matter what, it makes its way back into your cylinder. And oil INSIDE the cylinder is bad. It gets burnt in the combustion process. That itself is not really a big deal. Burning a little oil, therefor losing a little oil. If it was vented to the atmosphere like in the old days, you were still losing oil. But the problem is on modern fuel injected and computer controlled motors that it can really ruin the performance of your motor. Oil being burnt in the combustion process can cause detonation, which is bad. It can cause knock which is bad. If you get detonation you can physically harm your motor. If you get knock, your car will pull fuel and timing which means you have less power and performance and lessen MPG. It will also start to ruin things like your throttle body and cause it to not function properly because its all gummed up with sticky nasty oil and sludge.

So, how can you do something about this? If you have not heard before, there is a item called a catch can. Its pretty simple really. And lots of people use them on performance builds. However, I am in favor of any enthusiast using them no matter how much or little horsepower your car has and regardless if you race or track your car. A catch can is simple really. It is a..well...can. There are hundreds of variations from generic-fits-all to vehicle specific. But they all work on the same principal. It gets inserted between the outlet of the PCV valve where the pressure (and unwanted oil) exits the motor. One side is connected to the PCV outlet, and the other side feeds in to your intake track. So, you are literally just inserting a component in the middle of the system that already exists.


How does it work: A good catch can has a “media” of some sort in the top portion of the can. It works similar to how a catalytic converter works. It creates surface area for oil and gunk to stick to, the air passed by and goes out the other side of the can, and the unwanted oil drops to the bottom of the can. It is basically a “Trap” for that unwanted oil. You empty the can regularly (I do mine at oil change, and once in between) to keep it from over filling. If it overfills, you are defeating the purpose and just blowing oil into your cylinders again. Its pretty much maintenance free and easy to “use” and install.


So, do your engine a favor and purchase or make a catch can. After your car burns up what oil is in the system from years of neglect it will thank you. You might see better performance and at minimal, you will be protecting your engine from the harmful effects of positive crankcase ventilation recirculation. After you drive it around a few thousand miles and see just how much oil it collects, you will be shocked. And typically, the older or more mileages you have, the more worn your rings are, and the more oil you likely have poisoning your motor. It is a cheap and easy mod to be sure no unwanted oil gets in your cylinders. Look through your throttle body, is there oil pooled up in the intake manifold? You could benefit from a catch can.

Lastly, if you want to ditch the chance of oil getting back into your motor via the PCV system altogether; its also pretty simple. Get a catch can, and instead of routing that outlet hose of the catch can back into your intake track simply put one of those little breather filters on it. This allows the air pressure to escape as intended, but still collects and keeps the oil in the can. In the even that it does make it past the catch can, it will just make a little smudge on the underside of your hood you can wipe off easily (although that likely wont happen). You are keeping the ground and your car free of unwanted oil and everyone is happy.


Adding this after the fact. I just went and emptied mine, if you care to see. This is after about 3000 miles


Old posting, but just found this video where the chief engineer for the hellcat engine discussed the need to have oil removed from the intake air so it doesnt cause issues like knock :Skip to 14:20

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