Radium Engineering Air Oil Separator Kit Subaru WRX / STI 2002-2007

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High-powered modified Subaru engines tend to generate excessive blow-by oil and gasses. In these cases, an ordinary small catch can may quickly fill with oil and not be adequate. Like the Radium Engineering Subaru Dual Catch Can Kit, the AOS (Air Oil Separator) kit is responsible for keeping blow-by oil and other pollutants out of the intake pipe, manifold, turbocharger, and intercooler during all engine loads. The main difference is that an AOS system returns what is collected back into the oil pan so there is no servicing required.

The AOS is constructed of three CNC machined sections that screw together and are sealed with O-rings.


  • AOS Height: 6.94" (top of dipstick to bottom of AOS)
  • AOS Diameter: 3.45" Round
  • AOS Capacity: 20.3 oz (600mL)


  • Effectively raises the octane and increases engine performance with cleaner inlet air
  • Prevents oil buildup in the intake or intercooler system walls, throttle body, intake manifold, etc.
  • Lowers hydrocarbon emissions

What is included?

  • Machined aluminum Radium Engineering Air Oil Separator
  • Specially designed mounting bracket (see note at bottom of page)
  • All necessary SAE J30R7 rated PCV/Emissions hose
  • Coolant hoses and fittings
  • All necessary aluminum fittings and hose-ends
  • Stainless steel mounting hardware

20-0207-02 Mounting Compatibility

  • 02-07 Impreza WRX
  • 02-07 Impreza WRX STi
  • 04-08 Forester XT
  • 05-06 Saab 9-2X Aero