Air Oil Separator Vs Catch Can?
Air Oil Separator Vs Catch Can?
Maintaining a high-performance engine requires a solid understanding of how to manage blow-by gases and oil vapor within the Positive Crankcase Ventilation (PCV) system. For many car enthusiasts, particularly those driving turbocharged vehicles like a Subaru WRX or Toyota Tacoma, the choice between an Air Oil Separator (AOS) and a catch can is a pivotal decision. Both devices serve the same fundamental purpose—intercepting oil and fuel vapors before they can coat your intake manifold and valves—but they achieve this through vastly different mechanical approaches. Choosing the right one ensures your engine breathes clean air, maintains its octane rating, and avoids the catastrophic risks associated with engine knock.
Understanding the Mechanics: AOS vs. Catch Can
The primary difference between these two systems lies in what happens to the captured oil. An Air Oil Separator is a sophisticated, "set-it-and-forget-it" device. It uses internal baffles to separate oil from the air and then automatically drains that oil back into the engine's oil pan. This creates a closed-loop system that requires zero manual maintenance. Conversely, a catch can is a passive reservoir that simply collects the blow-by fluid. Because it does not return the fluid to the engine, the driver must manually empty the can on a regular basis to prevent it from overflowing and causing intake issues.
Pros and Cons for Your Daily Driver or Track Build
When deciding on the best modification for your vehicle, maintenance preference and cost are the biggest factors. An AOS is generally more expensive and features a complex installation process that may involve tapping into the vehicle's cooling system to prevent condensation from freezing in winter. However, the lack of required maintenance makes it ideal for daily drivers. Catch cans are more affordable and significantly easier to install, often being a simple "plug and play" setup. While they require frequent monitoring, they ensure that contaminated oil and moisture never find their way back into your clean oil sump.
| Feature | AOS vs. Catch Can Comparison |
|---|---|
| Oil Management | AOS returns oil to the engine; Catch can stores it in a reservoir. |
| Maintenance Level | AOS is maintenance-free; Catch can requires regular manual draining. |
Installation and Emissions Compliance
For those concerned with legalities and ease of use, the choice often tilts toward the AOS. Because most AOS units are closed systems that recirculate air back into the intake, they are generally considered emissions-compliant. Some catch cans, specifically "vent-to-atmosphere" (VTA) models, may violate local emissions regulations as they release vapors directly into the air. Furthermore, high-quality AOS units often include heating elements via coolant lines to ensure performance in cold climates, a feature rarely found in standard catch can kits.
FAQ about Air Oil Separator Vs Catch Can?
Will installing a catch can or AOS void my vehicle warranty?
Generally, these modifications do not void your entire warranty, but they could impact claims related to the PCV system if not installed correctly. Many owners choose to revert to stock before visiting a dealer for service.
How often should I empty a catch can?
Maintenance intervals vary based on your engine's health and driving style. Most experts recommend checking and emptying the can every 3,000 to 5,000 miles, or more frequently in cold weather when condensation increases.
Which is better for a track-driven car?
An AOS is often preferred for track applications because high G-forces can increase blow-by, and the automatic return feature ensures you do not run out of oil capacity during long sessions.
Conclusion
Whether you choose an Air Oil Separator or a catch can, adding an oil management system is one of the most effective ways to prolong the life of a modern turbocharged engine. If you value convenience and a clean engine bay without the need for manual checks, the AOS is the superior investment. If you are on a budget or prefer to monitor exactly what your engine is producing, a catch can offers an effective and affordable alternative. Ultimately, both paths lead to the same goal: a healthier, more efficient, and more reliable high-performance machine.