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Thread: Air Oil Separator vs Catch Can

  1. #1
    Senior Member test Mitsubaru's Avatar
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    Air Oil Separator vs Catch Can

    For my 2015 WRX, I've been reading up on my engine and people are recommending one or the other for my car because A) boxer engine and B) Direct Injection have known issues with out it. My only question is which is preferred?

    I know catch cans require dumping of the oil but when it's -40 out for 3 months, and the condensation freezes, wouldn't a catch can be a poor choice?

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    And then I've read some people say that an Air Oil Separator isn't as effective as a catch can since it dumps bad particle back into the engine. But it's maintenance free and there should be no condensation freeze up.

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    Administrator test MarcGSR's Avatar
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    Re: Air Oil Separator vs Catch Can

    I think you answered your own question. Do you mind doing a small amount of work to empty your catch can now and again or do you prefer maintenance free at the cost of a little performance (I mean, the particles were in your engine to begin with)? The choice is yours.

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    Senior Member test Mitsubaru's Avatar
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    Re: Air Oil Separator vs Catch Can

    Sorry. by bad particles I read that external engine particles, such as fuel and dust get sucked into the engine internals. I don't know how legit that is. This is just on forums that I've read up on.

    I'll clarify my question. Is a catch can more effective than an air oil separator? And does the condensation freeze up hold true?

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    Senior Member test Tremblay's Avatar
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    Re: Air Oil Separator vs Catch Can

    Oil filters clean out "bad particles"

    Engines and oil are built to handle contaminates. That's why you change your oil and don't leave it in there for 10 years at a time.

    A system that drains back into your pan makes more sense to me. Only reason I would run a can you have to drain out is if you wont want to take the time to empty out the can, or don't want to have the extra work of running a return line back to your sump.
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    Re: Air Oil Separator vs Catch Can

    Carbon build up will be a thing not matter what. It will reduce it, but you are still going to have carbon from combustion build up on valves. You are better of doing meth. Maybe Subaru's are different in design. But direct injection = carbon build up.

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    Senior Member test Mitsubaru's Avatar
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    Re: Air Oil Separator vs Catch Can

    Well I am already using this https://www.amsoil.com/shop/by-produ...ont%2fapi.aspx to help clean the carbon deposits.

    I use it approx. every 4000 miles.

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    I'm a HATER! test MiniD1CK5's Avatar
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    Re: Air Oil Separator vs Catch Can

    I have a piece of hose going into an ice tea bottle
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    Senior Member test Mitsubaru's Avatar
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    Re: Air Oil Separator vs Catch Can

    Quote Originally Posted by MiniD1CK5 View Post
    I have a piece of hose going into an ice tea bottle
    Please post a picture of this lol

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    Re: Air Oil Separator vs Catch Can

    Quote Originally Posted by Mitsubaru View Post
    Well I am already using this https://www.amsoil.com/shop/by-produ...ont%2fapi.aspx to help clean the carbon deposits.

    I use it approx. every 4000 miles.
    That's not going to help. At lest not on VW engines. The carbon build up is in the valves, away from fuel. It might burn cleaner, but not enough to actually help carbon build up.


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    Quote Originally Posted by MiniD1CK5 View Post
    I have a piece of hose going into an ice tea bottle
    I also did this temporarily to see my amount of blow by... Except I used a Starbucks jar and a bike water bottle mount. #classy

    Some people do the elephant trunk mod... And yes. You guessed it. A hose going from the valve cover to the ground. Just let it all drip back to where it came from. #classier
    Last edited by Clutched?; 04-29-2016 at 11:34 PM. Reason: Drunk edit

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    I'm a HATER! test MiniD1CK5's Avatar
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    Re: Air Oil Separator vs Catch Can

    Yup you're just wasting money with that amsoil additive.
    FUNCTION >FORM

    Randy Probst's take on the BRZ "it's like a BMW and a Lotus had a baby"

    "Adding power makes you faster on the straights. Subtracting weight makes you faster everywhere." -Colin Chapman

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    Re: Air Oil Separator vs Catch Can

    Quote Originally Posted by MiniD1CK5 View Post
    Yup you're just wasting money with that amsoil additive.
    It's also bull because it says it saves from using costly higher octane fuels.... It costs more than the filling up with 91 over 87.

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    I would get a catch can if you are set on filtering your vapours. It won't make much difference on its own for carbon build up, but is a useful tool. You will be able to see the oil you are losing. And it won't be a biweekly drain. Probably as often as you change your oil. And if you do have to drain it, I'm sure your engine makes enough heat to prevent water from freezing. Just put it around the turbo.

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    Premium Member test Nabs's Avatar
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    Re: Air Oil Separator vs Catch Can

    Most BMWs have the air oil separator from factory and you still get a very slight find on oil in the intake. I switched over to a catch can but it's not a vent to atmosphere, as most run it, and connects to the intake again (something to do with vacuum and pressure?) but it filters out quite a bit of condensation and oil. My catch can comes with a built in dipstick so I can check on the level every so often.
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    Re: Air Oil Separator vs Catch Can

    Quote Originally Posted by Clutched? View Post
    It's also bull because it says it saves from using costly higher octane fuels.... It costs more than the filling up with 91 over 87.

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    I would get a catch can if you are set on filtering your vapours. It won't make much difference on its own for carbon build up, but is a useful tool. You will be able to see the oil you are losing. And it won't be a biweekly drain. Probably as often as you change your oil. And if you do have to drain it, I'm sure your engine makes enough heat to prevent water from freezing. Just put it around the turbo.
    Turbo's at the bottom, lower than the oil pan lol.

    Here's a quote from Mishimoto.

    "Great question! This "catch tank" is located under the turbochargerunit itself. On this vehicle, the turbochargeris at a lower point than the oil pan. Oil supply from the engine passes through theturbochargerand into this tank. This fluid is then pumped back into the engine.

    This component does not serve the same function as a traditional catch can setup. The product we designed will reduce the amount of oil traveling from your CCV/PCV system into the intake tract. Keep an eye on the "Vendor Announcements" section in the next week or so, we will be starting a build thread regarding the project."



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    As for the Amsoil PI. Here's their tests results (of course, totally biased towards them...but still.)
    https://www.amsoil.com/lit/G2543.pdf

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    Re: Air Oil Separator vs Catch Can

    The mishimoto is for a an air oil separator I assume because it is returning back to the engine. A catch can be mounted anywhere because it catches and stores stuff. Put it on the firewall in an accessible spot, you know, for manual draining. I just mentioned turbo, as that would be hottest area of the engine bay.

    That cleaner will not remove carbon. It may burn cleaner, and thus less carbon. It will not remove. Its no better than just using a quality fuel.

    In the summary it doesn't say that it removes carbon, only that it improves emissions. It talks about valves and build up, and how you have less carbon deposits because of the cleaner burn. You would have to use it on every fill up, which isn't worth $12 a bottle. Set that aside for a manual cleaning.

    Furthermore, i mentions it can be used in Port or direct injection, which is basically saying don't dump it in a diesel. It doesn't specify the benifit to being used in direct injection. If I had the miracle cure for Carbon on DI I would make that my number one sell... So either it doesn't or their marketing is sleeping.

    Maybe Subaru is different with there upside down engine technology, but direct injection is going to have considerably more carbon build up because of where the fuel is injected. At some point, you will have to have your valves manually cleaned. Have you read about DI and why build up happens?
    Last edited by Clutched?; 04-30-2016 at 07:22 AM.

  15. #15
    Senior Member test Sooby's Avatar
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    Re: Air Oil Separator vs Catch Can

    Not sure if you're car has the same vaccum line setup as mine does(I'm sure it's very similar). If you it does you pretty much need to run 2 catch cans if you going that route, 1 for the pcv and then one for the valve cover breathers as well. I need to change the setup I have on mine cause I cheaped out and bought a shitty can. I don't think it's caught anything haha. For you an aos would be fine a grimspeed or Crawford one are probably the best

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