IAG AIR / Oil Separator (AOS) - 2015-2021 Subaru WRX & 2014-2018 Forester XT (FA20 DIT)

Essential Engine Protection for the Direct-Injected FA20
On the direct-injected 2.0L FA20 DIT engine found in the 2015–2021 WRX and 2014–2018 Forester XT, oil contamination in the intake system is a major performance threat. Under boost, crankcase pressure forces oil mist and blow-by vapors directly into your intake tract. Once inside, this oil coats the interior walls of your top-mount or front-mount intercooler, drastically reducing its ability to cool the air charge. Worse yet, when that oil enters the combustion chamber, it dilutes your fuel, lowers your effective octane rating, and induces dangerous engine knock. The IAG V3 Air Oil Separator (AOS) captures and separates oil mist before it ever reaches your intake, preserving horsepower, intercooler performance, and long-term engine health.

Patent-Pending Swirl-Pot Design with Integrated Heating
Unlike cheap catch cans that use simple wire mesh baffles and require constant manual emptying, the IAG V3 AOS is a permanent, maintenance-free solution. Its high-volume cast aluminum housing utilizes a multi-stage swirl pot layout that spins oil out of the crankcase air stream using centrifugal force. The separated oil automatically drains safely back down into your oil pan. To prevent cold-weather moisture buildup and the dreaded "milky sludge" common in northern climates, IAG routes engine coolant directly through the base of the separator body. This keeps the unit at engine operating temperature, completely eliminating condensation and freezing risks during winter driving.

• Stop Oil Contamination in Intake & Intercooler: Keep oil mist out of your intake, keeping intercooler cores clean and operating at maximum thermal efficiency.
• Prevent Engine Knock & Detonation: Stop crankcase oil vapors from entering the combustion chamber where they lower effective fuel octane and trigger knock retard.
• Heated Housing Technology: Taps into your factory cooling system to keep the AOS warm, preventing water condensation, sludge buildup, and freezing in cold climates.
• Maintenance-Free Drain-Back System: Automatically returns captured oil directly to the oil pan. No messy catch cans to manually drain at every gas fill-up.
• FA20 DIT Chassis-Specific Fitment: Includes vehicle-specific mounting brackets, custom-molded hoses, and quick-connect fittings designed exclusively for the VA WRX and SJ FXT engine bays.

Technical Specifications:

• Product Type: Air Oil Separator (AOS)
• Housing Material: Heavy-Duty Cast Aluminum
• Separation Method: Multi-Stage Swirl Pot & Baffling
• Thermal Control: Integrated Coolant Passage (Heated Base)
• Drain-Back Style: Automatic Gravity Drain to Engine Oil Pan
• Hose Construction: Custom Molded SAE-Rated PCV & Breather Hoses
• Engine Compatibility: 2.0L Turbo FA20DIT Boxer Engine
• Maintenance Requirement: Zero (Self-Draining System)

Fitment:

• Subaru WRX (VA Chassis): 2015, 2016, 2017, 2018, 2019, 2020, 2021 (2.0L Turbo FA20DIT)
  • Compatible with all trim levels: Base, Premium, Limited, Sport, Sport-tech, Series.HyperBlue, Series.Gray, and Series.White.
• Subaru Forester XT (SJ Chassis): 2014, 2015, 2016, 2017, 2018 (2.0L Turbo FA20DIT)

The Nameless "Installation" Pro-Tips:

Coolant Bleeding & Hose Slope Are Everything:

1. Maintain the Gravity Drain Angle: Liquid oil relies entirely on gravity to flow back into the engine block. When routing the bottom drain hose down to the FA20 crankcase port, double-check that the line maintains a smooth, continuous downward slope with zero low spots, dips, or "U" curves. Any sags in the line will trap oil and prevent the AOS from draining properly.

2. Watch Your Hose Clearance: The FA20 engine bay gets crowded near the pitch stop mount and firewall. Make sure all breather and PCV hoses are routed smoothly without tight kinks or sharp bends, and keep them clear of hot exhaust surfaces or sharp metal brackets.

3. Burp the Cooling System: Because installing the AOS requires tapping into your factory heater core lines to heat the housing base, you will introduce air pockets into the cooling system. Always finish the installation by thoroughly burping the cooling system using a spill-free funnel to ensure proper heater operation and stable coolant temperatures!