IAG AIR / Oil Separator (AOS) - 2008-2014 WRX, 2008-2021 STI, 2009-2013 FXT, 2005-09 LGT & OBXT

The Standard-Setting Engine Defense for High-Power EJ Engines
On turbocharged 2.5L EJ-series engines (EJ255 and EJ257), high boost levels and aggressive driving create intense crankcase pressure that pushes 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, severely degrading its ability to cool the intake 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 can contaminate your intake system, preserving horsepower, intercooler efficiency, 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.
• Chassis-Specific EJ Fitment: Includes vehicle-specific mounting brackets, custom-molded hoses, and SAE quick-connect fittings designed exclusively for 2.5L EJ 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: 2.5L Turbo EJ Boxer Engines (EJ255 / EJ257)
• Maintenance Requirement: Zero (Self-Draining System)

Fitment:

• Subaru WRX (GR/GV Chassis): 2008, 2009, 2010, 2011, 2012, 2013, 2014 (2.5L Turbo EJ255)
• Subaru WRX STI (GR/GV & VA Chassis): 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 (2.5L Turbo EJ257)
• Subaru Forester XT (SH Chassis): 2009, 2010, 2011, 2012, 2013 (2.5L Turbo EJ255)
• Subaru Legacy GT (BL/BP Chassis): 2005, 2006, 2007, 2008, 2009 (2.5L Turbo EJ255)
• Subaru Outback XT (BL/BP Chassis): 2005, 2006, 2007, 2008, 2009 (2.5L Turbo EJ255)

The Nameless "Installation" Pro-Tips:

Coolant Bleeding & Hose Slope Are Everything:

1. Maintain the Gravity Drain Path: Liquid oil relies strictly on gravity to drain back into the crankcase. When installing the bottom oil return hose, ensure the line maintains a smooth, continuous downward slope from the AOS canister to the engine block. Avoid any low spots, sagging bends, or "U" dips that can trap oil and back up the separator.

2. Take Care with EJ PCV & Head Breathers: The EJ255 and EJ257 feature distinct valve-cover breather and crankcase PCV ports. Follow IAG’s routing diagram carefully to ensure all lines connect to their designated AOS ports. Proper routing balances crankcase pressures across all cylinders under high boost.

3. Thoroughly Burp the Coolant: Splicing into your factory heater core lines introduces air pockets into your engine's cooling system. Always finish your installation by thoroughly burping the cooling system using a spill-free funnel to prevent air locks, heater core noise, or erratic engine temperatures!