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 patent pending 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
Posted by Chris
Once I found the install video on youtube for my particular year, the install was made easy.
Posted by Unknown
The install video available is pretty clear (except for which line is the Head breather lines luckily i knew already) I noticed a change in smell of the car immediatly as well as after the 1st 1000 miles i have not had new as much oil loss as before. A quart every 3k miles was pretty normal and its looking more like 1/4th a quart or less every 3k miles. I have heard of issues of a build up in the lines and havn'
t seen that yet but it hasn't been very long. There are better units out there but this one does he job and is the cleanest looking one.
Posted by mack
Was super excited to get this product but, when I went to install it, I was missing a bunch of connectors and the 5/8 hose.
GS Staff Note: Hey Mack, if you ever receive something from us that's not what you were expecting or is missing pieces, please get in touch right away and we'll get you sorted out. In this case, give us a call when you have a minute!
Posted by Daniel P.
I was curious about the AOS for some time but for the price I felt that I didn’t need it. I took my motor apart and saw I had a lot of overflow and decided to pull the trigger. After installing it I wish I bought it earlier! It feels sturdy, easy to install and looks clean. GREAT PRODUCT GRIMMSPEED!!!
Posted by 12wrx
Car now puts down slightly better power and the oil has been removed. Install is not the most direct and straight forward on the '11-'14 WRX but DIY persons can get it right with the correct research. Forums are very helpful. Looks great in red!
Posted by Justin Williams
The GS AOS is a beautiful piece of equipment and is super easy to install for the DIYers out there like myself! Went in very easily and functions flawlessly a must have for those of you who have upgraded turbos and/or just would like to get the performance out of the fuel you're using possible! Thanks GS for an amazing piece!
Posted by Mike Brophy
I recently did a stage 2 install and decided to go ahead and try this instead of the standard catch can. The install was about as easy changing your air filter and as far as i can tell its doing its job. I havent had time to take my TMIC off yet to see if there is any oil, but the STi is running better than ever.
Posted by Charlie Dinges
Awesome piece. Could not have been happier with the install and quality of the product. No reason to purchase anything else, this is it. Great job guys.
Posted by Greg Fleming
Very nice piece, every part felt heavy duty. Install is a breeze. I am very impressed with all parts from Grimmspeed, always top notch.
Posted by Chris Hoffman
I just wanted to let you know that all of you did a GREAT job with the GS Air Oil Separator. Since I have put it in, I haven't lost a single drop of oil. Having a built engine really began consuming a lot of oil. On my last 4,000 miles, I topped off over 5.2 quarts of oil. Having to constantly check my oil level is super tedious as well. Thank you so very much for such an amazing product!!