How does an oil catch can work and why is it beneficial?

Updated on February 5, 2026.

I've torn down enough engines to tell you a hard truth: what manufacturers call "emissions compliance," I often call "mechanical suffocation."

Every internal combustion engine has blow-by. It doesn't matter if it's a factory-fresh Ford F-150 or a tuned WRX. When combustion happens, high-pressure gases force their way past the piston rings and into the crankcase. This pressurizes the crankcase with a nasty cocktail of unburnt fuel, water vapor, and micro-particles of oil.

Decades ago, we just vented this to the atmosphere (draft tubes). Today, for environmental reasons, the Positive Crankcase Ventilation (PCV) system sucks this mess out and shoves it right back into your intake manifold to be burned off.

Here is the engineering flaw: You are feeding sticky, oily sludge into the precise airflow dynamics of your intake runners.

The "GDI" Nightmare: A Case Study

Let me tell you about a customer car I had on the lift last year. It was a direct-injected 2.0L Turbo with only 45,000 miles on the clock. The owner complained of rough idling and a noticeable drop in power. No check engine light, just a sluggish engine.

When I pulled the intake manifold, the problem was obvious. The intake valves looked like they were covered in burnt popcorn. Because Direct Injection (GDI) sprays fuel directly into the cylinder (unlike Port Injection, which sprays over the valve), there was no gasoline solvent to wash the oil vapor away.

That oil vapor from the PCV system had baked onto the hot valves layer by layer. We had to perform a walnut blasting procedure for four hours to clean it. A $150 oil catch can installed at mile 1 would have prevented that $800 repair bill.

Why Diesel Trucks (Cummins/Duramax/Powerstroke) Are Even Worse

If you drive a modern diesel, the situation is grimier. You have the PCV oil vapor mixing with soot from the EGR (Exhaust Gas Recirculation) system.

Oil Vapor + Soot = Grinding Paste.

I've seen intercoolers on diesel trucks that had a literal cup of oil sitting in the bottom boot. When your intercooler is coated in oil, its thermal transfer efficiency drops. Your intake air temps (IATs) go up, and your ECU pulls timing or fuel to compensate. You lose power, and you risk coating your expensive turbo compressor wheel in unbalanced sludge.

Selecting Hardware: Don't Buy an "Empty Can"

As an engineer, I look at fluid dynamics. There are cheap "eBay specials" that are just empty aluminum cans with two hose barbs. Do not buy these. The air moves too fast through them for the oil to separate. The vapor just goes in one side and out the other.

You need a device that changes the velocity and direction of the airflow. I recommend baffled catch cans (like the ones we engineer at SPELAB).

How a real catch can works:

• Impingement: The dirty air hits a metal plate (baffle). The oil is heavier than air, so it smacks the plate and drips down.
• Filtration: The air passes through a bronze or stainless mesh media to catch finer mist.
• Gravity: The clean air turns a corner and exits, while the heavy sludge stays at the bottom.

Factory parts are designed for minimum cost and warranty compliance. Aftermarket parts like these are designed for longevity and performance.

View the SPELAB engineering solution for your vehicle.

Frequently Asked Questions (Tech Specs)

Q: Will installing a catch can void my manufacturer warranty?

A: Technically, no. In the US, the Magnuson-Moss Warranty Act protects you. A dealership must prove that the aftermarket part caused the failure to deny a claim. However, since catch cans modify the emissions system plumbing, some strict dealerships may give you trouble. I always recommend saving your factory PCV hoses. It takes 10 minutes to swap back to stock before a dealer visit.

Q: How often do I actually need to drain it?

A: It depends on the season and your driving style. In the summer, you might drain it every oil change (3,000–5,000 miles). In the winter, you must check it more often—sometimes every 1,000 miles. Cold weather causes condensation, so the can fills up faster with a water/oil mixture that looks like a murky latte. Do not let it freeze.

Q: Does this add horsepower?

A: Directly? No. Indirectly? Yes. By preventing carbon buildup on valves, you maintain the engine's original airflow efficiency. Also, oil vapor effectively lowers the octane rating of your fuel. By keeping oil out of the combustion chamber, you reduce the risk of pre-ignition (knock), allowing your ECU to maintain optimal ignition timing.

Q: I have a Port Injected engine (older style). Do I need one?

A: It's less critical than for GDI engines, but still beneficial. While your valves stay cleaner due to the fuel wash, your intake manifold and throttle body can still get gummed up with oil varnish. If you are running high boost (forced induction), I absolutely recommend one regardless of injection type.

Q: Can I just vent the PCV to the atmosphere instead of using a catch can?

A: I don't recommend it for a street car. Venting to atmosphere (VTA) smells terrible—you will smell burning oil at every stoplight. It also makes a mess in your engine bay and is illegal in all 50 states for emissions compliance. A catch can is a closed-loop system that keeps the smell contained and the EPA happy.

Q: What happens if the catch can gets full and I forget to empty it?

A: This is the danger zone. If the can overfills, liquid sludge can be sucked into the intake manifold. In a worst-case scenario, if a large slug of liquid enters the cylinder, you could hydro-lock the engine (bend a connecting rod). This is why checking it regularly is part of the ownership responsibility.

Q: Why don't cars come with these from the factory?

A: Cost and maintenance. Manufacturers save millions by using a simple plastic hose instead of a machined aluminum can. Furthermore, the average driver barely knows how to check their oil level. Telling a consumer they have another tank to empty every month is a marketing nightmare for an OEM. They trade long-term reliability for short-term convenience.

Q: Is a "Universal" catch can okay to use?

A: As long as the internal baffling is good, the can itself works fine. The headache is the mounting and plumbing. Vehicle-specific kits (like SPELAB's) come with pre-bent brackets and hoses cut to the exact length with the right quick-connect fittings. It turns a 3-hour frustration into a 20-minute install.

John Lee

Mechanical Engineer | 10+ Years Experience

John has spent the last decade engineering and testing high-performance automotive components. Specializing in drivetrain durability and thermal management across Powerstroke, Cummins, and Duramax applications, he bridges the gap between OEM limitations and aftermarket performance. His philosophy: "Factory parts are just a starting point."