RADIUM Engineering 20-0258-00 Air Oil Separator AOS-R Kit for 2015+ Subaru WRX

The RADIUM Engineering AOS-R (Air Oil Separator with Return) Kit is a complete plug-and-play solution designed to eliminate harmful blow-by contamination in 2015+ Subaru WRX engines. Unlike traditional catch cans that require constant draining, this advanced system automatically returns separated oil back to the oil pan, providing maintenance-free operation while protecting your intake system, turbocharger, and intercooler from oil vapors and deposits.

Key Features:

• CNC machined billet aluminum construction with 20.3 oz (600mL) capacity separator can
• Built-in coolant heater prevents water condensation and features an integrated water trap system
• Two-step oil separation baffling with cleanable, reusable stainless steel filter media
• Returns collected oil automatically to the oil pan—no servicing required
• Includes Subaru-specific mounting bracket and Radium Master Cylinder Brace (20-0255)
• Complete kit with all SAE J30R7-rated PCV/emissions hoses, coolant lines, aluminum fittings, and stainless steel hardware
• O-ring sealed dipstick for easy inspection
• Installs on left-hand side of engine bay near brake master cylinder

How It Works: High-performance and modified Subaru FA20F engines generate excessive crankcase blow-by containing oil vapors and gases. The AOS-R effectively separates these contaminants before they enter the intake manifold, preventing carbon buildup on intake valves—a critical concern for direct-injected engines. The water trap design, combined with the integrated heater, ensures any moisture is trapped and eventually evaporated rather than contaminating the oil pan.

Performance Benefits: Cleaner intake air increases engine performance and effectively raises fuel octane. Prevents oil buildup in intake system components and lowers hydrocarbon emissions. Compatible with 2015+ Subaru WRX and 2014-2018 Subaru Forester XT with FA20F engine (LHD vehicles only).

Note: For vehicles operated in freezing climates, insulation sleeving (sold separately) is recommended for hoses exposed to cold airflow.