08-14 WRX / 05-12 Legacy GT GrimmSpeed Air Oil Separator

GrimmSpeed Air/Oil Separator , 2002-2007 Subaru WRX / 2004-2021 STI

The GrimmSpeed Air/Oil Separator for the 2002-2007 Subaru WRX / 2004-2021 STI intercepts oil vapor from the crankcase ventilation system before it enters the intake tract, preventing the oil buildup on intercooler cores, charge pipes, and intake valves that is a known issue on turbocharged Subaru platforms. A straightforward installation with long-term maintenance and performance benefits.

DETAILS

• Separates oil vapor from crankcase ventilation air
• Prevents oil buildup on intake components
• Easy-drain collection reservoir
• Color: natural aluminum
• Includes all installation hardware
• Fitment: 2002-2007 Subaru WRX / 2004-2021 STI

The EJ series engine’s crankcase ventilation system recirculates blow-by gases back into the intake tract , a requirement for emissions compliance. These gases carry oil vapor that gradually coats the intercooler core, charge pipes, and intake valves with an oil film. On the TMIC-equipped Subaru platforms, oil coatings on the intercooler reduce cooling efficiency. On direct injection engines, intake valve deposits from oil vapor are a known long-term issue.

The GrimmSpeed AOS separates the oil vapor from the blow-by gases before they re-enter the intake , clean air continues into the intake, oil collects in the AOS reservoir for periodic draining. Installation connects inline with the existing PCV system. The reservoir drain allows captured oil to be drained during regular maintenance without removing the unit.

What’s in the Box

• GrimmSpeed AOS unit
• Fittings and lines
• Hardware
• Instructions

Why Choose GrimmSpeed

GrimmSpeed has been engineering performance parts for Subaru platforms from their Portland, Oregon facility since 2003. Everything they make is designed around real-world use , their engineers drive the same cars their customers drive, which means product decisions are made with genuine platform knowledge behind them. GrimmSpeed designs parts in-house, sources quality materials, and validates fitment on the actual application before release. The result is parts that install correctly the first time, perform as advertised, and hold up under the conditions Subaru owners actually subject their cars to. Whether it is a critical engine component or a cosmetic upgrade, the same attention to detail and fit quality applies across the catalog.

The RallySport Take

The AOS is one of those modifications that owners often wish they had installed earlier once they see how much oil collects in the reservoir. On a daily-driven turbo Subaru, it is a practical maintenance modification that protects expensive intake components from oil contamination. Fits the 2002-2007 Subaru WRX / 2004-2021 STI.

Fitment