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Old 05-28-2018, 11:41 PM   #1
benpdavid
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Exclamation Freezing Dangers of AOS/Catch Cans - IAG AOS

Many new owners (especially those with FA20DIT) may consider adding a catch can or air-oil-separator (AOS) in order to prevent carbon deposits on their engine's intake valves and/or to prevent octane reduction of their cylinder-charge by oil vapors. This is widely considered a good preventative maintenance measure (especially on modified cars), but there is a very real risk associated with the use of these after-market parts in colder climates which is typically dismissed by the companies selling these products.

The blow-by gasses which these products work to filter contain a large amount of water vapor because this is one of the primary products of combustion. During cold weather this water vapor can condense and freeze in the catch can or AOS body as well as the hoses which run to and from it. If this happens you will typically pressurize the crankcase (depending on what freezes). Hopefully your dipstick, or a hose connection will be blown out to relieve the pressure, leaving you with an oily mess, but no real damage. However, you may not be so lucky. If the pressure does not release in this way, it will find the next easiest path - potentially blowing out your turbo seals or worse.

Some AOSs on the market attempt to reduce the likelihood of this scenario by heating the can or separator with coolant. However, this does not eliminate the risk of its hoses freezing solid. I learned this the hard way after installing an IAG Street Series AOS on my 2017 WRX. (by the way - IAG claims that a properly installed AOS poses no risk whatsoever). In fact, due to it's plumbing and installation, the IAG Street Series AOS poses an additional risk in comparison to catch cans or vented-to-atmosphere AOSs.

The Street Series AOS eliminates the factory PCV valve and increases the amount of blow-by gas which would typically pass from the PCV into the intake manifold. After filtering it, the AOS sends it to the turbo inlet instead (some will still be sent to the manifold if it is under vacuum). Besides resulting in a closed AOS system, this works to reduce the ethanol vapors in the crank-case if you are running e85 and is why it is suggested for these builds.

My issue arose when my AOS's drain line froze. Instead of draining the separated oil back to the crankcase, the oil filled the AOS and was sucked through my turbo and the rest of my intake system and engine. I was on the highway when this occurred and I was not being as vigilant as I should have been, so I'm not sure how long it was occurring without readily noticeable symptoms. However, eventually my engine faltered and died with the low-oil light coming on. At this point I had the vehicle towed and serviced. I learned that over 2/3 of the engine's oil had been consumed in this way. I had as much oil as possible removed from the intake system, and I had the AOS bypassed. Additionally, my upstream catalyst was poisoned/damaged by the oil passing through the exhaust - necessitating it's replacement. I was incredibly fortunate that there was no further damage, but I wanted to share my experience with others in the hope that they could avoid the same fate I did.

For those who do opt to install an AOS or catch can(s) in colder climates, I would strongly urge you to opt for a coolant-heated can/AOS and to add insulation to the lines in an effort to reduce your risk of failure. Also, check our oil level at every fuel fill-up, if not more frequently, during periods of extreme cold. If your car is not significantly modified, you may by better off avoiding one altogether.
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Old 05-29-2018, 09:24 PM   #2
Backroad Rex
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Been running the IAG Comp series for 50,000+ miles with no problems. Mid-Michigan. But good to know....
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Old 05-29-2018, 11:46 PM   #3
benpdavid
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Quote:
Originally Posted by Backroad Rex View Post
Been running the IAG Comp series for 50,000+ miles with no problems. Mid-Michigan. But good to know....
Glad to hear you’ve had better luck than myself. I had my AOS installed for around 13,000 miles (driving in Wisconsin and Illinois) before the incident.
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Old 05-30-2018, 06:19 AM   #4
ntron1
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Wow! I would have never thought that water could stay frozen in an engine bay with temps @ 100+ when driving. Especially long enough to allow an IAG AOS to fill with oil. Learn something new every day.
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Old 05-30-2018, 06:55 AM   #5
benpdavid
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Quote:
Originally Posted by ntron1 View Post
Wow! I would have never thought that water could stay frozen in an engine bay with temps @ 100+ when driving. Especially long enough to allow an IAG AOS to fill with oil. Learn something new every day.
I was too. I think it’s due to the fact that some of those lines are routed near the air blast from the hood scoop.
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Old 05-30-2018, 07:04 AM   #6
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Default Additional Info.

After posting this I found another thread with some great info:

https://forums.nasioc.com/forums/showthread.php?t=2461224

It suggests pulling over and idling now and then on long highway drives to rebuild heat under the hood. It also has some great suggestions if your find yourself in the situation of freezing up.
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Old 05-30-2018, 01:43 PM   #7
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Had an IAG Comp AOS on my 14 STI for 60k kms. Never had an issue with freezing and Winnipeg is known for being colder than the surface of Mars. We average -25 to -35 degrees Celsius during the winter.

Check the routing of your lines and make sure none are kinked.
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Old 05-30-2018, 05:14 PM   #8
benpdavid
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Quote:
Originally Posted by Nurp View Post
Had an IAG Comp AOS on my 14 STI for 60k kms. Never had an issue with freezing and Winnipeg is known for being colder than the surface of Mars. We average -25 to -35 degrees Celsius during the winter.

Check the routing of your lines and make sure none are kinked.
Thanks for the suggestion, but none of the lines were kinked. Also, the drain line was verified to be frozen solid.
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Old 10-21-2020, 08:39 AM   #9
pmjohnson06
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Default Erie PA temps

Thank you for your post, its appreciated. I am looking into a AOS for my 2018 WRX as a protective measure and was keeping the extreme cold of Erie winters in mind. So what did you end up doing? Wrapping your lines in insulation or just take occasional pit stops when driving around during winter months? Is there a AOS that you would recommend?
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Old 10-21-2020, 09:32 AM   #10
KillerBMotorsport
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Insulating the drain line helps considerably, we offer a cold weather option (take from aviation) specifically because of this issue.

Something to keep in mind though, is that PCV lines can clog/freeze shut even when everything is 100% stock. This is why the FSM includes inspection/replacement of the crankcase and vent lines.

We do not heat/cool our AOS, aside from the extremely hot blow-by gasses going through it.
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Old 10-21-2020, 03:25 PM   #11
Vancouver98STi
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Lightbulb Relative humidity also makes a big difference

Quote:
Originally Posted by Backroad Rex View Post

Been running the IAG Comp series for 50,000+ miles with no problems. Mid-Michigan.
Quote:
Originally Posted by benpdavid View Post

I had my AOS installed for around 13,000 miles (driving in Wisconsin and Illinois) before the incident.
Quote:
Originally Posted by pmjohnson06 View Post

I am looking into a AOS for my 2018 WRX as a protective measure and was keeping the extreme cold of Erie winters in mind.
Quote:
Originally Posted by Nurp View Post

Never had an issue with freezing and Winnipeg is known for being colder than the surface of Mars. We average -25 to -35 degrees Celsius during the winter.
I think it's critical to mention that it's not just cold temperatures that can lead to an AOS system freezing up, it's also got a lot to do with relative humidity.

If humidity levels are low, then freezing cold temperatures probably don't create much of a problem with an AOS system. Here on the coast, winter temperatures are normally rather mild. However, the relative humidity is usually always quite high. My oil catch can system captures quite a bit of water year round (and needs to be emptied on a regular basis), so when it does drop below freezing here, a plugged breather system is a genuine concern of mine. Fortunately, I have a car other than my STi to drive when weather conditions turn ugly.
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Old 10-21-2020, 03:52 PM   #12
KillerBMotorsport
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Quote:
Originally Posted by Vancouver98STi View Post
I think it's critical to mention that it's not just cold temperatures that can lead to an AOS system freezing up, it's also got a lot to do with relative humidity.
There are a lot of factors that come into play, including environmental. RH will have less of an effect if you spend more time at temperature vs a 2 mile commute to work every day.

H2O is a byproduct of combustion, which has a far more pronounced effect if you drive the car distances, and condensation can occur anywhere the air cools and/or expands like in an AOS. There is ALWAYS moisture on cooler internal surfaces, like your oil cap for example, and especially the factory metal PCV lines that attached to the intercooler. That makes for a great heat sink for condensation to occur. It's a fairly common part to be replaced on high mileage cars in the northern regions.

The other thing to consider here is that MANY factor play into how much blow-by you have. Oil type, brand, and weight. Driving style, length of time driving, and conditions (highway or city). Fuel type, power output, build specs, and even engine wear all play a part in how much blow-by an engine has. LOTS of variables here. One of our shop cars builds up next to nothing on internal surfaces and it's making a crap load of power on a built engine running flex fuel. Another is essentially stage 2 and it builds up much quicker.
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Old 10-21-2020, 10:54 PM   #13
Vancouver98STi
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Quote:
Originally Posted by KillerBMotorsport View Post

There are a lot of factors that come into play...
Of course. The only point I was making was that everything else being equal, an AOS/oil catch can will collect more condensation/water (and potentially freeze up) in cold locations where the relative humidity is high.

Last edited by Vancouver98STi; 10-22-2020 at 12:00 AM.
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Old 10-21-2020, 11:19 PM   #14
Trob
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I run two oil catch cans. I live in Alaska. Northern Alaska and have never had them freeze. I also run 50/50 meth. Probably why if doesn’t freeze and the hot as hell has going in to it.
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Old 10-22-2020, 08:35 AM   #15
benpdavid
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Quote:
Originally Posted by pmjohnson06 View Post
Thank you for your post, its appreciated. I am looking into a AOS for my 2018 WRX as a protective measure and was keeping the extreme cold of Erie winters in mind. So what did you end up doing? Wrapping your lines in insulation or just take occasional pit stops when driving around during winter months? Is there a AOS that you would recommend?
Actually posted what I did in another thread, and while I’m sure there’s a way to link it, I don’t know how so I’m copy/pasting it below. If you’re making the power where you really need a catch can I’d still probably go for the IAG. Their new design should also keep the system a little hotter. The one downside to their new design is that without a coolant port on top you won’t be able to easily route the entirety of the return gas hose alongside a coolant hose for heating. Probably okay to just insulate that portion though. I actually work for a diesel engine company and we require CCV insulation at a minimum for applications which will operate below freezing. Testing the systems almost always finds that line heating is also required.

“I made thermocouples with k-type wire and hooked them up to a cheap led display/controller I found on amazon. I put one on each of the 3 pipes i felt were at greatest risk (aos inlet to intake manifold, aos drain to crankcase, and aos inlet to crankcase) and ran them through a switch. I taped the thermocouples to the rubber lines with aluminum tape, added self-regulating heating cable like this (LINK), ziptied them in place, and wrapped them with more aluminum tape (this is to help heat transfer from the heat trace to evenly heat the rubber tube). Then I covered them with line insulation like this (LINK). The other AOS lines either run with the coolant lines or in factory locations so I wasn't worried about them freezing. Since I have my EGR deleted I removed all the 90degree connections in the aos lines I could with straight adapters. This made heat tracing them easier since the cable isn't very flexible.

It may have been a little overkill, but it worked well last winter and I like having the peace of mind. If you have any questions and I'll be happy to answer them.”
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Old 10-22-2020, 11:01 AM   #16
KillerBMotorsport
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Quote:
Originally Posted by Vancouver98STi View Post
Of course. The only point I was making was that everything else being equal, an AOS/oil catch can will collect more condensation/water (and potentially freeze up) in cold locations where the relative humidity is high.
Of course, I would agree with that. The point I was making is that everything else is never equal
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Old 10-22-2020, 04:33 PM   #17
Vancouver98STi
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Cool Plenty of variables...

Quote:
Originally Posted by KillerBMotorsport View Post

The point I was making is that everything else is never equal
You neglected to mention that driving into a lake may increase AOS water collection.
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Old 10-27-2020, 12:42 PM   #18
ericsson
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is this issue specific to IAG AOS?
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Old 10-27-2020, 01:24 PM   #19
oichan
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I have a BoombaRacing catchcan (stage1 only) on my 19 WRX Limited.. the car sits outside 24/7 even through -20F weather. No issue I've encountered.

My STI has a Grimmspeed AOS and no issue. My STI is parked indoors and only driven occasionally on dry winter days so used a lot more mildly vs my WRX.
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Old 11-01-2020, 03:03 PM   #20
TheClutchRider
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i do have issues with moisture building up in the crank case with the IAG AOS.
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