Radium AOS-R Air Oil Separator Kit (2015+ WRX/ 14-2018 Forester XT)

SKU: 20-0258-00 Category:



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 built-in heater keeps water from condensing in the AOS. And because water is more dense than oil, there is an integrated water trap found around the bottom perimeter of the can. This prevents water from descending into the oil pan if ever present. Furthermore, because the water is trapped against the heater, it will eventually boil and evaporate out of the system. The AOS is constructed of CNC machined sections that screw together and are sealed with O-rings. The AOS can be completely disassembled for cleaning or servicing.

Package Contents

  • Radium AOS-R Air Oil Separator
  • All necessary SAE J30R7 rated PCV/Emissions hose
  • Coolant hoses and fittings
  • PCV delete fitting
  • All necessary aluminum fittings and hose-ends
  • Stainless steel mounting hardware
  • 20-0225 Master Cylinder Brace

*If operated in freezing environments, Radium Engineering recommends installing insulation sleeving (not included) over any hose exposed to cold air flow. This will help prevent the natural phenomenon of water condensation freezing and potentially clogging the hose. 


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Confirmed Fitment

Year Make Model
Year Make Model
2014 - 2018 Subaru Forester XT
2015 - 2021 Subaru WRX