Air/Oil Separator - WRX/STI/LGT/FXT


Current stock: 0

It appears that you’re not the only one with excellent taste in premium automotive components! Unfortunately, the red 08-14 WRX/05-09 LGT AOS is temporarily out of stock, however should become available soon. You can still place your order and be put in a queue; the item will be shipped ASAP. Please contact our customer service via email or phone (612-379-0000) with questions, or check for availability with our retailers, thanks!

Most COMPLETE and COMPACT Air/Oil Separator on the market!

An Air/Oil Separator has one job, remove the oil from the engine ventilation system so the oil does not get sent through the intake system. 


The GrimmSpeed™ Air/Oil Separator for Subaru vehicles has a unique design that allows you to maintain your PCV Valve while separating the oil out of the crankcase and head ventilation air! Our AOS will allow your engine to run more efficiently due to the separation of oil from the intake system. When there is oil in your system, the result is 1) reduced fuel octane 2) higher chance of engine knock(detonation) 3) worse emissions 4) higher oil consumption. Our Air/Oil Separator will help all of these problems

In typical GrimmSpeed™ fashion, we have made a very compact unit that packs a powerful punch(and looks good while doing it)! 

No more having to check/empty your catch can and refilling your oil. The GrimmSpeed™ AOS coalesces oil without using a mesh media. Mesh medias can cause contaminates to collect and build up resulting in possible sludge. Our AOS is self maintained so you can just sit back, stop worrying, and enjoy driving your car

Please note this product is designed to combat factory amounts of blow by. If you have a built motor or are experiencing abnormal amounts of oil consumption, this product may not work for you.


Air/Oil Separator FAQ:
Q: Is this beneficial on a street car?
A: Yes. Even in stock form, you will experience oil going through your intake system. If you have ever looked in your intercooler piping you will notice a bunch of oil build up on the inside, our AOS takes care of this problem.

Q: I've heard about the milky oil substance in cold climates when using an AOS, is that relevant?
A: During our testing here in the frozen tundra of Minnesota we have only noticed very minimal milky substance from the AOS. Condensation is allowed to collect on the inside of the core but will evaporate when the engine gets up to running temps.

Q: Why choose the GrimmSpeed™ AOS over other AOS products?
A: The GrimmSpeed™ AOS allows you to separate the vapors from both the heads and the crankcase. Others on the market only allow you to separate the vapors from the head. Also, our AOS allows you to retain the OEM PCV Valve. Being that it allows you to do both of these things at the same time makes it the most complete AOS on the market.

Q: How will this AOS increase my octane?
A: When the oil vapors are mixed into the intake system, it effectively lowers the octane which can cause detonation. Installing our AOS will eliminate the oil vapors in your intake system thus eliminating the loss of octane. On modified cars this let's you get more aggressive with your timing/boost maps and will allow you to make more power!

Q: Do I need to carry around a 19mm socket to open it?
A: No, we have sized the cap nut to be the same size as a lug nut. So as long as you have a tool to take your lug nuts off(which you should always have in your car), you will have a tool to open the AOS. On a proper running system you shouldn't need to open the AOS very often.

Q: How big is the unit compared to the oem oil cap? I'm running a FMIC and need to make sure it will fit
A: We created it so it will work perfectly with a FMIC as well. The body of our AOS as the same diameter as the oem oil cap.

Q: What models will this fit?
A: Our will fit EJ series turbo Subaru engines

GrimmSpeed Subaru Air Oil Separator

08-14 Turbo Subaru Air/Oil Separator Install InstructionsPDF Document Icon

See below for install videos.

14 Reviews

Josh 13th Dec 2020


Awesome product, looks good and does the job perfectly.

Deeds 6th Feb 2018

Those with Built Engines or Running in Colder Climates Be Aware!

Firstly I'll note that the overall build quality is great like all GrimmSpeed products. This is not the AOS you want to be running on any built engines. I've tried it on two different EJ builds and it has done more harm than good. This is stated here in red below the product description, but it should be better known. It may be in part due to combining a built engine with colder climate, but this AOS is horrible in cold climates. I'm not much further north than Minnesota, and this AOS design is extremely poor for holding condensation and even dumping it back down the oil fill tube along with the oil that is separated. The issue seems to be with the components not getting hot enough in the colder climates. I've experienced excessive amount of condensation and milk build up, almost plugging off lines and the ports of the AOS itself. For winter I've even blocked off my hood scoop and insulated the lines and the AOS manifold itself with minimal improvements. This product may very well work great on a completely OEM engine. Just be cautious of any other application.

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