Radium Air/Oil Separator Kit | 15-21 Subaru WRX / 14-18 FXT (20-0258-00)

When a built FA20 fills a catch can faster than you can drain it, the system needs to drain itself.

High-powered modified Subarus generate blow-by beyond what a small can absorbs between services. The Radium Engineering Air/Oil Separator (AOS-R) Kit intercepts blow-by oil and pollutants before the intake pipe, manifold, turbocharger, and intercooler at all engine loads, then returns the collected oil to the engine automatically for a service-free system. A coolant-fed heater keeps water from condensing inside, and an integrated water trap around the bottom perimeter holds any water against that heater until it boils off, so only clean oil drains back, never milky sludge. It mounts to the Radium master cylinder brace on the LH side of the bay, plumbed as a completely sealed system to the turbo inlet.

What You'll Feel

• Set-and-forget crankcase management with no can to check or drain, ever
• Cleaner inlet air effectively raising octane on a knock-sensitive turbo engine
• An intercooler and intake tract staying free of oil film through track abuse
• Only oil returning to the pan, with the heater and water trap evaporating condensation out of the system
• Lower hydrocarbon emissions from a fully sealed circuit

Features

• Machined aluminum AOS-R assembly: 3.45" diameter, 20.3 oz (600mL) capacity, heated by engine coolant
• Integrated water trap around the bottom perimeter prevents water from reaching the oil pan
• PCV valve replaced by a custom machined straight-through adapter fitting; collected oil drains back into the engine block through it
• Outlet plumbed to the turbo inlet pipe for a completely sealed system
• Mounts to the Radium brake master cylinder brace: 20-0258-00 includes the 20-0255 brace, 20-0258-01 is for cars that already have it (brace REQUIRED either way)
• SAE J30R7 rated PCV/emissions hose, coolant hoses and fittings, aluminum fittings and hose-ends, stainless hardware

The Details

The AOS-R differs from a catch can in one fundamental way: instead of storing what it separates, it drains the oil back to the engine, which is why moisture management becomes the engineering problem. Water condensing in a normal can just gets dumped at service time, but water draining into an oil pan is bearing damage waiting to happen, and Radium's answer is the coolant heater plus density-based water trap, where trapped water sits against the heated surface until it evaporates out of the sealed circuit. Installation lives on the LH side near the brake master cylinder, with the brace doing double duty as chassis stiffener and AOS mount; choose 20-0258-00 to get the brace in the box or -01 if your car already wears one. One climate note from Radium: in freezing environments, install insulation sleeving (not included) over any hose exposed to cold airflow to keep condensation from freezing and clogging the line. Left hand drive FA20F cars only.

Kit Includes

• 1x Machined aluminum AOS-R assembly with specially designed mounting bracket
• SAE J30R7 rated PCV/emissions hose, coolant hoses and fittings
• PCV delete (straight-through) adapter fitting
• All necessary aluminum fittings and hose-ends, stainless steel hardware
• 20-0258-00 only: 20-0255 brake master cylinder brace included

Applications

• 2015-2021 Subaru WRX (FA20F, left hand drive only)
• 2014-2018 Subaru Forester XT (FA20F, left hand drive only)
• Requires the Radium master cylinder brace (included in -00, separate for -01)