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Ill be the first to ask. What is this for? And why wouldn't it come from the factory with one if it's needed?
I'm assuming it's related to the whole direct injection issue where there ends up being carbon build up on valves after some time. There's videos of people walnut blasting them on Youtube to fix them.

Disclaimer: We don't know if this engine will have this issue, but it's assumed we will like other DI engines.
 

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Ill be the first to ask. What is this for? And why wouldn't it come from the factory with one if it's needed?
Not a single turbo Subaru comes with an oil separator. So far to date, all of them can benefit. We get a PCV valve and it all gets recirculated back into the intake.

Here is a wonderful illustration from Radium Engineering which shows how dual catch set up works.

Idle ....



WOT



I used these to plumb in 2 separate catch cans. The idle can picks up so much more oil. Meaning it cleans the intake charge while idling, this helps limit detonation when you get on it after sitting. The WOT can catches blow by under power, which helps limit detonation as well. Of course direct injection helps, but if you have oil in the intake charge, that will contribute to detonation.

Crawford and AEM have some fancy systems that drain back to the crankcase. For like $350. You can build a dual system with cheap catch cans for about $100-150.
 

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Discussion Starter · #6 ·
I won't go into the technical minutiae, suffice to say that all direct injected only engines can benefit from the use of an air/oil separator. Oil vapor blow by into the air charge can and will result in carbon fouling on valves. The extent to which that will cause issue for this platform has yet to be determined but a couple hundred $$ is cheap piece of mind for me. I have used Moroso cans in other applications with success but I was curious what other were running on Subaru. This will be my first Subie so I'm not as familiar with these vehicles.
 

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So did anyone install an Oil Separator/Catch Can? I saw in another line of posts that it is already used on a Subaru Ascent. To be Clear " I am confused"
Built into the design. It's mounted on the driver's side of the turbo. I have video someplace, but, in the meantime, here's a drawing courtesy of @denissh .
1435
 

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Do you happen to know if this "catch can" exists for other Subaru models, namely the new Crosstrek and Forester which also have updated GDI engines?
Sadly, I don't have their service manuals, so, alas, I do not. Next time I renew my STIS subscription or get to Competition Subaru of Smithtown to borrow their screen, I will check, if no one else knows.
 

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Do you happen to know if this "catch can" exists for other Subaru models, namely the new Crosstrek and Forester which also have updated GDI engines?
it's not on 2019 Forester , looks like its only on new 2.4 turbo

but on new 2.5 (like 2019 Forester ) they have electrical "COOLING - Thermo Control Valve"
 

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Just to clarify, I think the original poster was referring to an oil catch can in relation to catching oil from the breather system, keeping it out of the intake.

The oil catch tank shown in the above pics is the area the turbo drains into since it's below the engine. It is certainly an oil catch can/tank/area, but that's part of the engine/turbo oiling system rather than the breather system.

An air/oil separator separates air from oil as the name implies, preventing oil and reducing oil vapor from getting from the engine's crankcase and valve cover area, into the intake system and eventually into the combustion chamber. I could go on for quite a while about all the reasons oil getting where you don't want it is detrimental, but a few big ones are it can cause misfiring and damaging engine knock, foul spark plugs and oxygen sensors, damage cat converters, it sticks to valves and causes them to attract debris which builds up until it causes more engine knock and misfiring from valves not sealing or flowing properly.

COBB partnered with IAG on this air/oil separator unit for the 15+ WRX which also has a DIT engine. You can see a bit of how it works here: https://www.cobbtuning.com/products/air-oil-separators/subaru-air-oil-separator-wrx-2015-2019
We can certainly investigate offering something for Ascent in the future.

-Mike @ COBB
 

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COBB partnered with IAG on this air/oil separator unit for the 15+ WRX which also has a DIT engine. You can see a bit of how it works here: https://www.cobbtuning.com/products/air-oil-separators/subaru-air-oil-separator-wrx-2015-2019
We can certainly investigate offering something for Ascent in the future.

-Mike @ COBB
Thanks for bringing the tech to the table on this thread. I have seen the benefits of AOS systems in my own cars. I have an IAG on my 2006. Very well executed. The market is only getting bigger with the 2020 LGT and Outback XT.

:love:
 

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Just to clarify, I think the original poster was referring to an oil catch can in relation to catching oil from the breather system, keeping it out of the intake.

The oil catch tank shown in the above pics is the area the turbo drains into since it's below the engine. It is certainly an oil catch can/tank/area, but that's part of the engine/turbo oiling system rather than the breather system.

An air/oil separator separates air from oil as the name implies, preventing oil and reducing oil vapor from getting from the engine's crankcase and valve cover area, into the intake system and eventually into the combustion chamber. I could go on for quite a while about all the reasons oil getting where you don't want it is detrimental, but a few big ones are it can cause misfiring and damaging engine knock, foul spark plugs and oxygen sensors, damage cat converters, it sticks to valves and causes them to attract debris which builds up until it causes more engine knock and misfiring from valves not sealing or flowing properly.

COBB partnered with IAG on this air/oil separator unit for the 15+ WRX which also has a DIT engine. You can see a bit of how it works here: https://www.cobbtuning.com/products/air-oil-separators/subaru-air-oil-separator-wrx-2015-2019
We can certainly investigate offering something for Ascent in the future.

-Mike @ COBB
Has there been any updates on the AOS from IAG or any other company @COBB Tuning ? I contacted several companies which said it “could” be coming soon but so far no product torment. I am in favor of a set it and forget more elaborate air oil separator than a less expensive catch can which needs periodic attention. These can be purchased universal fit or pieced together.
As others have pointed out; a few hundred bucks is cheap insurance despite the interesting design of our 2.4L DIT PCV system attempting to limit this carbon buildup.
 

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Ill be the first to ask. What is this for? And why wouldn't it come from the factory with one if it's needed?
Short answer: to separate crankcase oil from air prior to discharging into intake
Long answer: Since the 1970 EPA Clean Air Act, the gov't began creating restriction on air emission on vehicles, not allowing pollutants to be vented into the atmosphere w/o treating them. So all of the systems in the cars have to operated in a closed-loop. The oil/air separator is commonly utilized to treat the crankcase gas, containing air/blow-by/oil, prior to sending/looping it to the intake track for re-combustion.

Cobb is selling them for $300-500 each separator kit. Perhaps it's not feasible for Subaru to include it. Instead they use a PCV (look it up ... you're on your own... lol), a common device on inline engine, to separate oil/air. Oil/air separator is a common device on all modern Porsche flat engines.
 

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Short answer: to separate crankcase oil from air prior to discharging into intake
Long answer: Since the 1970 EPA Clean Air Act, the gov't began creating restriction on air emission on vehicles, not allowing pollutants to be vented into the atmosphere w/o treating them. So all of the systems in the cars have to operated in a closed-loop. The oil/air separator is commonly utilized to treat the crankcase gas, containing air/blow-by/oil, prior to sending/looping it to the intake track for re-combustion.

Cobb is selling them for $300-500 each separator kit. Perhaps it's not feasible for Subaru to include it. Instead they use a PCV (look it up ... you're on your own... lol), a common device on inline engine, to separate oil/air. Oil/air separator is a common device on all modern Porsche flat engines.
Since such devices must be closed-loop due to EPA restrictions, the oil/water they capture must be drained periodically. In some cars and with some catch cans, forgetting to empty the reservoir can result in blown seals. This is one of the reasons car manufacturers do not include them. Imagine them instructing their customers that they have to empty a catch can every month or so on a modern vehicle.
 
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