Are Oil Catch Cans Worth It?

Oil catch cans are a popular modification on high performance and tuned vehicles, but there is a lot of speculation and general confusion as to what they do and whether or not they work. Are catch cans better at preventing carbon build-up than the systems cars come with from the factory? Read on to learn the function of an oil catch can and see if it’s worth installing one on your car!

What Does an Oil Catch Can Do?

The goal of an oil catch can is to intercept fine oil particles in the PCV system before they are recirculated through the engine intake.
On an engine’s combustion stroke, a small amount of vaporized air, fuel, and oil makes it past the piston rings and enters the crankcase. The PCV (Positive Crankcase Ventilation) valve redirects this vapor out of the crankcase and back into the intake.

While the PCV system keeps harmful vapors out of the crankcase, saving the engine from acidic oil, excessive crankcase pressure, and damage from water condensation, it’s not foolproof.

The harmful vapors that are purged from the crankcase can cause carbon buildup on the intake valves and manifold, a dirty throttle body, and liquid in the intercooler on vehicles with forced induction. These particles may contaminate the air-fuel mixture in the cylinder, reducing power output. Oil catch cans collect and condense the vapor into a liquid, reducing the amount entering the intake.

How do Oil Catch Cans Work?

Oil catch cans capture vaporized oil, fuel, and other particles, condensing them into a liquid. Air and particles enter the catch can when they are purged from the crankcase via the PCV valve.

Inside, the air is forced through a system of baffles, filter, or an open container depending on the design. the oil vapor and other contaminants from engine blow-by are condensed or absorbed, remaining in the bottom of the catch can. The clean air makes its way out and enters the intake with less harmful particles.

Do oil catch cans work?

This is up for debate. When considering whether or not they catch and collect particles from engine blow-by, then yes, they do work. But, how well they work depends a lot on the design of the catch can.

 A paper published by SAE found that based purely on filter quality, airflow drop rate, and particle capture efficiency, aftermarket catch cans fell far below OEM and OEM style systems. Open catch cans in particular (those without any filtration or baffling) are extremely ineffective. This test was performed on diesel vehicles, but still provides insight into the overall effectiveness of aftermarket catch cans.

SAE Study Results

The figures below show the results of 3 aftermarket catch cans compared to a highly effective OE version. The full study is free to download. It breaks down the methods used, and analyzes other OEM and OEM style oil separators.

The above figure looks at wet and dry pressure drop at different flow rates. “Wet” pressure drop refers to the difference in pressure seen after the catch can has been saturated with oil. “Dry” pressure drop refers to the pressure difference seen in a non-saturated catch can.

The second figure shows the efficiency of after market oil catch cans. Efficiency measures the amount of particles captured at a specific flow rate.

The study found that the three aftermarket oil catch cans fell below OEM systems in all areas tested.

Remember, this study tested only three aftermarket designs. These results are not indicative of the performance of all aftermarket catch cans.

Next, and perhaps the most important unknown factor, is whether or not using a catch can actually prevent carbon buildup, improve performance, and prevent damage to the intercooler/charge system. Do engines recirculate enough particles to hinder performance, and does removing these particles with a catch can remedy that?

Conclusion

Oil catch work by capturing harmful particles from engine blow-by. However, research has shown that aftermarket catch cans lack the efficiency of OEM counterparts. With so much variation in the development of aftermarket parts, it is hard to tell an effective oil catch can from an ineffective one. Without an extended side by side comparison, it is impossible to say for sure if there is any benefit to using one.