What is a Catch Can? | Revv.ly Glossary

What is a Catch Can?

I've seen engines opened up after 100,000 miles that looked like they'd swallowed a bucket of sludge--intake valves caked with deposits, ports restricted with gunk, everything coated in a greasy film that shouldn't be there. And I've seen engines with similar mileage that looked nearly new inside. One key difference? The healthy engines often had catch cans fitted. It's not glamorous, but it's one of the most sensible modifications you can make.
A catch can intercepts oil vapors from the positive crankcase ventilation (PCV) system before they reach the intake manifold. Modern engines, particularly direct-injected ones, route these vapors back into the intake to be burned--environmentally conscious, but mechanically problematic over time. The catch can gives those oil vapors somewhere to go that isn't your intake valves.

The Problem It Solves

Every internal combustion engine produces blow-by--gases that escape past piston rings into the crankcase. These gases carry oil vapor with them. The PCV system vents these vapors, and emissions regulations require they be routed back into the engine rather than released into the atmosphere.
In port-injected engines, fuel spraying onto the intake valves provided constant cleaning. But direct injection sprays fuel directly into the cylinders, bypassing the valves entirely. Those oil vapors accumulate on valve faces and in intake ports, building up into carbon deposits that restrict airflow and, eventually, cause problems.
Symptoms of severe carbon buildup include:

• Rough idle
• Reduced power and efficiency
• Misfires under load
• Poor throttle response
  The fix--walnut blasting or chemical cleaning--costs hundreds of dollars and hours of labor. A catch can helps prevent the problem from developing in the first place.

How They Work

The catch can sits in-line with the PCV system. Oil-laden vapor enters the can, where baffles or filter media cause oil droplets to coalesce and fall to the bottom of the can. Cleaner vapor continues to the intake. The collected oil is periodically drained or the can is emptied.
Better catch cans include:

• Baffled designs -- Internal plates force vapor to change direction, helping oil droplets separate
• Filter elements -- Steel mesh or similar media that captures oil while allowing air through
• Drain valves -- Allow easy emptying without removing the can
• Sight windows -- Let you see how much oil has accumulated

Installation and Maintenance

Most catch cans install in-line with the PCV hose. One end connects to the valve cover fitting, the other to the intake manifold or PCV valve. Some installations are simple; others require creative routing.
Maintenance is minimal but important: empty the can regularly. On some cars in cold climates, you'll be surprised how much accumulates. On others, there's barely anything. Either way, checking periodically ensures the can is working and doesn't overflow.

The Quality Spectrum

Catch cans range from $30 eBay specials to $300+ engineered solutions. The differences matter:
Budget Cans -- Basic reservoirs with minimal or no baffling. They work to some extent but separate oil less effectively. May not seal properly or may be too small for some applications.
Mid-Range -- Baffled designs with decent construction. Mishimoto, Moroso, and similar brands offer functional options at reasonable prices.
Premium -- Highly engineered solutions from companies like Radium Engineering or OEM+ options from performance brands. Maximum separation efficiency, quality materials, proper drainage.
For most applications, a mid-range catch can provides the protection you need. The extreme options make sense for high-boost applications or those who want the absolute best.

The Long-Term View

I think of catch cans as inexpensive insurance. They don't add power. They don't improve the driving experience today. But they keep your engine cleaner, potentially prevent expensive problems, and contribute to long-term reliability.
On the Revvly community, owners share their catch can findings--how much oil they're catching, which brands work best for their platforms, and the results of intake inspections.
Related: OEM, Preventive Maintenance, ECU
Direct-Injection Platforms Needing Catch Cans: VW GTI MK6/MK7, BMW N54/N55, Ford EcoBoost