All about Subaru's Original Air Oil Separator & Why You Need One

by Cody Woodruff February 19, 2018

What is a Subaru Air Oil Separator?

The Crawford Performance Air Oil Separator (AOS) is the original solution to Subaru's notorious oiling system issues. Although the technology was pre-existing with other vehicle brands such as Porsche, Crawford Performance is the inventor of the first system specifically for Subaru. No other AOS on the market employs the same technology.



What does an Air/Oil Separator do?

Just as an air cleaner separates the dirt from the air going in to your engine, an AOS separates the oil from the air going into your engine.

What are the benefits of having an AOS vs. a catch-can?

An AOS uses centrifugal force to force your engine’s oil through an internal labyrinth system, which makes the oil separate from engine condensation. A catch-can simply collects oil and requires one to either manually empty or pour back in the same, dirty oil. An AOS will automatically drain clean, separated oil back into your engine, without any maintenance required whatsoever. Just install and forget.


Why does every Subaru engine need one?

Subarus engines are notorious for higher than average oil consumption. They are horizontally opposed, meaning that their pistons move side to side. G-Forces push excess oil to the tops of the pistons. Since oil is naturally combustible, this causes irregularities with the controlled explosion that happens in this environment, subsequently creating multiple explosions. Another word for this is detonation — an engine killer. Over time, this excess oil begins to build up making the detonation more frequent and damaging. Detonation is what causes the infamous ‘ringland failure’: a term that all of us Subaru owners have become unnecessarily accustomed to. This failure is amplified when modifying power components. Any added stress/heat from power components and higher G-Forces increases the amount of excess oil that ends up in your intake. Having a secondary system is your fail-safe for detonation that is un-related to a poor tune. Not only will you consume less oil, the lack of excess helps to maintain the ultimate mixture in your cylinders which in turn maximizes your power output. This allows your Subaru's engine to purr efficiently at its full potential, without having to worry about your avoidable detonation.


What makes a Crawford AOS stand above the rest?

  • It is the original. Our V3 has the latest technology not seen anywhere else; patent pending.
  • We offer the only Dual Chamber system in the industry, without the need to delete any smog components for installation.
  • Takes half the time to install compared to other AOS kits.
  • The Crawford AOS is the only design that forces oil through a labyrinth system, with each change of direction increasing the separation efficiency.
  • No coolant leaks. Each canister is put through a pressure test post-manufacturing.

What are the differences between versions?

In 2005, the V1 was our original design on our race vehicles. We were suffering consistent engine failures due to oil starvation and excessive detonation. Adapting concepts from other manufacturers solutions, we engineered our own swirl pot solution to keeping oil out of the intake. Due to our warmer climate here in Southern California, our testing did not cover frozen climates. When the product was launched worldwide, colder and frozen climates experienced condensation. Cold air from the hood scoop would hit the canister right on, creating the condensation and water to form on the inside. Water and oil do not mix, so this environment was not allowing the canister to perform it's job of separating the two. We recalled the V1 and replaced it with the V2.
The V2 features an added coolant bypass line to keep the canister at operating temps at all times, solving the condensation issue.
*Please note, since the V2 AOS Kit removes the PCV valve from the smog system, it is for off-road use only in CA.

In most recent years, we have released our best design yet: the V3.
Unlike the V2, it does not delete your PCV valve during installation. This is a required smog component in California*. Since the V3 utilizes the PCV system, the V3 has 2 chambers inside the canister: one sees vacuum form the PCV valve, and the other sees the pressure from the oil system. When in vacuum, the dirty air from the crankcase is sucked out via the PCV valve through one chamber of our V3, and when in boost the dirty air is sucked out of the crankcase through the second chamber of our V3. This means clean air is always entering the valve covers. Each chamber has it's own labyrinth inside, which increases the separation efficiency from that of the V2. Lastly, proximity to the engine heats the system so that it no longer requires a coolant bypass line. This simplifies install, making our V3 AOS Kits take half as long as any other AOS system on the market to bolt up.
While our V3 AOS is our most efficient design for separation, it is not designed to hold large volumes of oil that are typically pushed into the valve covers in higher G scenarios such as a road race course. We recommend using the V2 for track setups, and the V3 for daily driving.
The V3 is still somewhat of a new release, so please bear with us as we continue to R&D further fitment options for those of you who have upgraded to a front mount intercooler and/or rotated turbo. See below for all current fitments.

In August of 2018, the newest line of the Crawford AOS was launched: The Baja Edition. In 2016, Crawford Performance took on an off-road race car with the support of Subaru of America: The Crosstrek Desert Racer. This is Subaru's first ever venture in to the American off-road scene, and they chose the Crosstrek engine to power the class 5 open car chassis. Naturally, Crawford Performance used this new race program to engineer and put their components to the ultimate test before releasing anything for the street market. The first Baja Edition AOS was engineered and helped the Crosstrek engine in the race car cross thousands of miles in the desert without oil starvation. Similar to the V2 AOS, this design uses a single chamber. Instead of seeing pressure as the V2 system does on a turbocharged engine, the Baja Edition utilizes the vacuum from the PCV system. This means only 2 ports are needed, making it incredibly easy to install. This line will eventually cover all N/A Subaru models, and more.
The Baja Edition AOS Line is brand new, so please bear with us as we continue to R&D further fitment options for more N/A Subaru models and more. See below for all current fitments.

Please do not leave questions in the comments section. There is no way for us to reply that notifies you that we did so. Please instead send us an email or give is a call.

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V2 Kit Fitment List by Vehicle

  • 2004 Subaru STI
  • 2005 Subaru STI
  • 2006 Subaru STI
  • 2007 Subaru STI

S0714-1: Designed to fit with Top Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower.

S0715-1: Designed to fit with Front Mount Intercoolers that are accompanied by a Stock Location or Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2002 Subaru WRX
  • 2003 Subaru WRX
  • 2004 Subaru WRX
  • 2005 Subaru WRX
  • 2006 Subaru WRX
  • 2007 Subaru WRX

S0714-1: Designed to fit with Top Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower.

S0715-1: Designed to fit with Front Mount Intercoolers that are accompanied by a Stock Location or Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2004 Subaru Forester XT
  • 2005 Subaru Forester XT
  • 2006 Subaru Forester XT

S0714-1: Designed to fit with Top Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower.

S0715-1: Designed to fit with Front Mount Intercoolers that are accompanied by a Stock Location or Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2008 Subaru STI
  • 2009 Subaru STI
  • 2010 Subaru STI
  • 2011 Subaru STI
  • 2012 Subaru STI
  • 2013 Subaru STI
  • 2014 Subaru STI

S0720 (Replaced S0713-1 & S0716-1): Designed to fit with Top Mount or Front Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower. (V3 Kit also available for this application)

S0720-1 (Replaced S0716-2): Designed to fit with Front Mount Intercoolers that are accompanied by a Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2015 Subaru STI
  • 2016 Subaru STI
  • 2017 Subaru STI
  • 2018 Subaru STI
  • 2019 Subaru STI

S0720 (Replaced S0713-1 & S0716-1): Designed to fit with Top Mount or Front Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower. (V3 Kit also available for this application but for top mounted intercoolers only)

S0710: Designed to fit with Front Mount Intercoolers that are accompanied by a Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2008 Subaru WRX
  • 2009 Subaru WRX
  • 2010 Subaru WRX
  • 2011 Subaru WRX
  • 2012 Subaru WRX
  • 2013 Subaru WRX
  • 2014 Subaru WRX

S0720 (Replaced S0718): Designed to fit with Top Mount or Front Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower. (V3 Kit also available for this application but for top mounted intercoolers only)

S0720-1 (Replaced S0718-1): Designed to fit with Front Mount Intercoolers that are accompanied by a Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2005 Subaru Legacy GT (LGT)
  • 2006 Subaru Legacy GT (LGT)
  • 2007 Subaru Legacy GT (LGT)
  • 2008 Subaru Legacy GT (LGT)
  • 2009 Subaru Legacy GT (LGT)

S0720 (Replaced S0718): Designed to fit with Top Mount or Front Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower.

S0720-1 (Replaced S0718-1): Designed to fit with Front Mount Intercoolers that are accompanied by a Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2007 Subaru Outback XT (OXT)
  • 2008 Subaru Outback XT (OXT)
  • 2009 Subaru Outback XT (OXT)

S0720 (Replaced S0718): Designed to fit with Top Mount or Front Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower.

S0720-1 (Replaced S0718-1): Designed to fit with Front Mount Intercoolers that are accompanied by a Rotated Turbo. Unit is mounted on the pitch stop.

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  • 2007 Subaru Forester XT (FXT)
  • 2008 Subaru Forester XT (FXT)
  • 2009 Subaru Forester XT (FXT)
  • 2010 Subaru Forester XT (FXT)
  • 2011 Subaru Forester XT (FXT)
  • 2012 Subaru Forester XT (FXT)
  • 2013 Subaru Forester XT (FXT)

S0720 (Replaced S0718): Designed to fit with Top Mount or Front Mount Intercoolers that are accompanied by a Stock Location Turbo. Unit is mounted on the passenger side strut tower.

S0720-1 (Replaced S0718-1): Designed to fit with Front Mount Intercoolers that are accompanied by a Rotated Turbo. Unit is mounted on the pitch stop.

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V3 Kit Fitment List by Vehicle

  • 2013 Subaru BRZ
  • 2014 Subaru BRZ
  • 2015 Subaru BRZ
  • 2016 Subaru BRZ
  • 2017 Subaru BRZ
  • 2018 Subaru BRZ
  • 2019 Subaru BRZ
  • 2013 Scion FR-S
  • 2014 Scion FR-S
  • 2015 Scion FR-S
  • 2016 Scion FR-S
  • 2013 Toyota GT86
  • 2014 Toyota GT86
  • 2015 Toyota GT86
  • 2016 Toyota GT86
  • 2017 Toyota GT86
  • 2018 Toyota GT86
  • 2019 Toyota GT86
  • 2017 Toyota 86
  • 2018 Toyota 86
  • 2019 Toyota 86

S0711: Designed to fit with any modifications. Unit is mounted centered between the two strut bars.

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  • 2015 Subaru WRX
  • 2016 Subaru WRX
  • 2017 Subaru WRX
  • 2018 Subaru WRX
  • 2019 Subaru WRX

S0717: Designed to fit with Top Mount Intercoolers. Unit is mounted right in front of the brake fluid reservoir. (more fitments in R&D)

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  • 2014 Subaru Forester XT
  • 2015 Subaru Forester XT
  • 2016 Subaru Forester XT
  • 2017 Subaru Forester XT
  • 2018 Subaru Forester XT

S0717: Designed to fit with Top Mount Intercoolers. Unit is mounted right in front of the brake fluid reservoir. (more fitments in R&D)

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  • 2008 Subaru STI
  • 2009 Subaru STI
  • 2010 Subaru STI
  • 2011 Subaru STI
  • 2012 Subaru STI
  • 2013 Subaru STI
  • 2014 Subaru STI
  • 2015 Subaru STI
  • 2016 Subaru STI
  • 2017 Subaru STI
  • 2018 Subaru STI
  • 2019 Subaru STI

S0699: Designed to fit with Top Mount Intercoolers. Unit is mounted right behind the coolant tank. On 2015+ STi's, the sound generator gets deleted. (more fitments in R&D)

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  • 2008 Subaru WRX
  • 2009 Subaru WRX
  • 2010 Subaru WRX
  • 2011 Subaru WRX
  • 2012 Subaru WRX
  • 2013 Subaru WRX
  • 2014 Subaru WRX

S0699: Designed to fit with Top Mount Intercoolers. Unit is mounted right behind the coolant tank. (more fitments in R&D)

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  • 2007 Subaru Forester XT
  • 2009 Subaru Forester XT
  • 2010 Subaru Forester XT
  • 2011 Subaru Forester XT
  • 2012 Subaru Forester XT
  • 2013 Subaru Forester XT
  • 2014 Subaru Forester XT

S0699: Designed to fit with Top Mount Intercoolers. Unit is mounted right behind the coolant tank. (more fitments in R&D)

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Baja Edition (NA) Kit Fitment List by Vehicle

  • 2013 Subaru XV Crosstrek
  • 2014 Subaru XV Crosstrek
  • 2015 Subaru XV Crosstrek
  • 2016 Subaru Crosstrek
  • 2017 Subaru Crosstrek

S0698: Unit is mounted on the drivers side of the intake manifold.

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  • 2012 Subaru Impreza 2.0i
  • 2013 Subaru Impreza 2.0i
  • 2014 Subaru Impreza 2.0i
  • 2015 Subaru Impreza 2.0i
  • 2016 Subaru Impreza 2.0i

S0698: Unit is mounted on the drivers side of the intake manifold.

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  • 2014 Subaru Forester
  • 2015 Subaru Forester
  • 2016 Subaru Forester

S0698: Unit is mounted on the drivers side of the intake manifold. For non-turbo model only.

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  • 2018 Subaru Crosstrek
  • 2019 Subaru Crosstrek

S0696: Unit is mounted on the drivers side of the intake manifold.

Please do not leave questions in the comments section. There is no way for us to reply that notifies you that we did so. Please instead send us an email or give is a call.

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