PCV Oil Catch Cans

The PCV Oil Catch Can Explained

To better understand the purpose of a good quality PCV Oil Catch Can and why they are important, we need to first understand the purpose of your Stock PCV System:

The PCV (Positive Crankcase Ventilation) system on your engine is designed to regulate and remove fumes from the engine crankcase, and to alleviate crankcase pressure which could cause oil leaks or seal damage. It’s a system for gases to escape in a controlled manner from the crankcase of an internal combustion engine.

During normal operation of an internal combustion engine, there’s a compressed air and fuel mixture inside the combustion chamber that is ignited and as a result, forces the piston downward.

A small amount of that ignited mixture leaks past the piston rings and ends up in the crankcase.

This leakage is often referred to as “blow-by” (leakage past the piston rings), as well as oil mist.
Some of the oil mist and other products settle along the engine intake and over time form a hard coating or “gunk.”

Looking further at piston ring design, all modern engines are built with low tension piston rings to reduce parasitic loss so if the crankcase does not have suction on it, the piston rings at higher RPM's loose stability and enter a state of rapid vibration known as "Ring Flutter". This creates even more blow-by and power loss and oil consumption issues.

For a specific example, let’s take a look at an LS engine because it’s easy to visualize. An LS3 engine draws the crankcase vapors out the valley cover. The filtered fresh MAF metered make-up air that enters the passenger side valve cover to flush and make up for the contaminant laden vapors being drawn out of the valley PCV barb only flushes that side of the valvetrain, so if you look underneath at the color and condition of each side valve cover, you’ll see the acids and moisture condense at the highest points of the crankcase as the engine cools after running. This result will discolor and eat away at the steel baffle and the raw aluminum; the passenger side will be relatively clean and corrosion free. These acid droplets falling onto the rocker arms also attack the stamped steel retaining caps and over time they can loosen and fall out allowing the needle bearing to break and fail. This is just one example, on one engine type.

Enter the PCV Oil Catch Can - a good quality, well designed oil catch can will collect that oil mist and condenses the fuel vapors while allowing “cleaner” gases to be passed back into the intake. If these contaminates are kept inside the combustion chamber, they will eventually make their way into the oil inside the crankcase and cause oil contamination and dilution or make their way back into the intake manifold.

This problem has been documented in many automotive magazines; Car & Driver had an article covering this topic (Carbon Deposits with Direct Injection), and there are hundreds of images on the Internet of Carbon Build up on Intake Valves.

The purpose of a well-engineered oil separating Catch Can is to route these gasses through a baffle system that provides the most contact possible with the outer surface resulting in the oil being trapped and removed from the other gasses that do continue through the intake and are burnt and consumed. Typically, the trapped oil is captured in the bottom of the Catch Can.