Subaru WRX 15-21 Forester XT 14-18 Air Oil Separator Kit - Includes 20-0255 (AOS-R)
Click here to download installation instructions (PDF)
COMPATIBILITY
15-21 Subaru WRX (LHD)
14-18 Subaru Forester XT (LHD)
OVERVIEW
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. The AOS-R (Air Oil Separator-Return) 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-R 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-R. 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-R is constructed of CNC machined sections that screw together and are sealed with O-rings. The AOS-R can be completely disassembled for cleaning or servicing.
BENEFITS
-Effectively raises the fuel 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
INSTALLATION
The Radium Engineering AOS-R kit installs on the LH side of the engine bay, near the brake master cylinder. The outlet (side port) of the AOS-R is plumbed back to the turbo inlet pipe, creating a completely sealed system. The AOS-R mounts to the provided Radium Brake Master Cylinder Brace. The PCV valve is replaced by a custom machined straight-through adapter fitting, shown below. Oil collected in the AOS-R drains out the bottom fitting and back into the engine block through this fitting.
INCLUDES
-Machined aluminum AOS-R assembly
-Specially designed mounting bracket
-SAE J30R7 rated PCV/Emissions hose
-Coolant hoses and fittings
-PCV valve 10AN adapter fitting
-All necessary aluminum fittings and hose-ends
-Stainless steel mounting hardware
-Brake master cylinder brace 
DIMENSIONS
AOS-R Height: 6.3" (without fittings)
AOS-R Diameter: 3.45" Round
AOS-R Capacity: 20.3 oz (600mL)
PORTS
Inlet: 7/8"-14 threaded for 10AN ORB fittings
Outlet: 7/8"-14 threaded for 10AN ORB fittings
Return: 7/8"-14 threaded for 10AN ORB fittings
Coolant: 7/16"-20 threaded for 4AN ORB fittings (x2)
NOTE: 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.