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Your car’s engine has a very intricate way of taking care of itself. For example, when oil blowby occurs, the engine is set up to recirculate the oil through the engine again; however, that can lead to power loss over time unless you install an oil catch can. But what is a catch can, and is it illegal to install one in your car?

What is oil blow-by?

NRG Performance Catch Can
NRG Performance Catch Can | NRG Performance

To understand what an oil catch can is, you first need to know what oil blow-by is. In a typical four-stroke engine, there is an intake stroke, which lets the air-fuel mixture into the cylinder; the compression stroke, which compresses that air/fuel mixture; the power stroke, which is when the spark (from the plugs) ignites the mixture and forced the piston back into the cylinder; and the exhaust stroke, which is when the exhaust gas is pushed out of the cylinder.

During the compression stroke, an immense amount of pressure is built up, so much so that a small amount of air can escape from around the piston rings. This is called “blow-by,” and the higher the RPM your engine spins, the more blow-by it will have. Fortunately, every engine has a PCV system that vents the crankcase – and the blow-by – and routes it back into the engine’s combustion chambers to safely burn them up.

Why would anyone want to use an oil catch can?

Every PCV system works the same way – there is a PCV breather valve that sits atop the engine valve cover, which vents the blow-by through a hose and into the intake manifold to route it back into the engine. It’s a simple and effective way to get that oil and fuel mixture out of the engine, but the constant re-cycling and re-burning can eventually lead to oil and carbon buildup on the engine’s valves.

This is especially true if your car has a “direct-injected” engine since these types of engines spray fuel directly into the combustion chamber. The solution is to use an oil catch can, which is a canister that has a filter and baffles in it, along with two hoses to connect to the valve cover and the intake manifold.

When oil blow-by occurs, the mixture is sent into the oil catch can, which filters it and circulates the air back into the combustion chamber. The end result is that your engine will have cleaner valves and combustion chambers over time.

Is hooking up an oil catch can to your engine illegal?

While smog laws can vary by state, it is typically illegal to install an oil catch in your car’s engine bay, according to Although a catch can could help your car’s engine run well for a long time, modifying the PCV system is illegal since it’s part of the engine’s emissions system. If a technician were to see an oil catch can installed on your car while performing an emissions test, they may fail you on the spot.

However, if you can legally install an oil catch in your state (check your local laws), then your car can benefit from not having that nasty oil and fuel mixture recirculated back into it. The only tough part is locating it somewhere convenient in the engine bay and remembering to empty it out from time to time, reports Road and Track.

But if you don’t want to have to worry about any of that, then stick with the stock PCV system. After all, it’s your engine’s way of taking care of itself.


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