Plumbing an AOS (Air Oil Separator)

Speedie6

Speedie6

Silver Member
Before starting this thread, I did a forum search for air oil separators. Didn't find a lot, but I found this thread:

Oil Catch Can Froze Up...Car Consumed Excessive Oil | Mazdaspeeds.org, the number one resource for all things Mazdaspeed!

In that thread, @Enki mentioned the Radium product:

Universal Air Oil Separator-Return (AOS-R) (radiumauto.com)

I know that Radium makes top-notch stuff. But I know that a lot of Subby's use IAG's:

IAG Air / Oil Separator (AOS) Fits 2022+ Subaru WRX (iagperformance.com)

In any case, I'm not fully understanding the oil return. On the Radium page, it says:

"For the AOS-R to function properly, a return port on the engine must be available on the engine to the oil pan."

That's the part I'm not sure how to do right. I've heard of plumbing the oil return to a port on the PCV plate. But presumably that would have positive pressure, cuz, that's where we are pulling pressure out of. So I'm not seeing how the return to there would work. So, how does it work?

I've actually watched an install video on a Subby for the IAG. And they say, "here's a place for you to pipe the return oil to". I'm not particularly familiar with Subby's, but I would figure a Subby wouldn't be that much different as far as the PCV system goes. But I'm not really sure where they are plumbing that oil return to.
 
Enki said:
Pressure in the AOS is equalized, thus allowing the oil to flow back into the pan.
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So you can just plumb it back to the PCV plate?

I noticed that the Radium has only one inlet. The IAG has 2 or 3. With the Radium, how would you connect the valve cover? I guess you would have to Y it together with the PCV connection?
 
The product page is a little vague. But, it appears that it actually does have two inlets. I've sent an email to Radium to clarify connections. And also to confirm they would recommend plumbing the oil drain back to the PCV plate. You see, before my current catch-can setup, I actually once had a Crawford AOS on my car. The AOS was mounted above the PCV plate and the oil drain was plumbed to it. Somehow, the oil backed up and coated my intercooler. Complete disaster. I don't know what specifically went wrong.
 
Enki said:
I already have one, and might be persuaded to do a shoot.
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A "shoot", a video?

I went ahead and put one on order. I had a back and forth with their tech support to ask a few questions. He said that the VTA option has two inputs, but the VTE (pipe back to the engine) only has one input. I asked wouldn't someone getting the VTE also want two inputs? His response:

"Yes in the cases of multiple breathers they'd have to split the inlet port to two ports."

He then said it was originally designed for a Subby application and provided a diagram of how it was intended to be connected to the Subby.

I asked what exactly is the difference between the VTA and the VTE, wouldn't you just have an unused connection on the VTA and be just the same as the VTE? He said,

"On the VTA version of our AOS-R, the outlet is the entire top of the can. The top has a baffle plate that covers and contains the filtration media and the can breathes around the groove around the outside edge. There is no port on the VTA outlet to connect to.

It is done this way to maximize the function of the catch can in the vent to atmosphere configuration. Catch cans perform best when you can maximize the amount of airspeed reduction that happens inside the can. Since we're venting to the open air, we aren't restricted by a hose connection and that allows us to have a very large outlet. The large outlet facilitates a large reduction in air speed, allowing the air in the can to slow and more effectively condensate in the filtration media and separate oil contaminants from the air before passing through the outlet.

The VTE will have a large chamber inside to slow air, but it will also taper down to the smaller outlet which speeds air back up. You can use the VTE can and just install a small filter onto the outlet, but it only has one inlet and won't perform it's function as well as the purpose built VTA can does."

I asked if piping the return oil to the PCV plate is the best way? Would it maybe make sense to run the return directly into the oil pan? He said,

"A bung to the oil pan technically can be done, but has to be above the oil level. It really isn't ideal as it is usually too close to the oil level and windage will usually push oil into the AOS from there. It cannot be submerged or it will just pull oil in. That port is best utilized low enough to drain, but high on the crankcase to keep away from oil. The PCV plate is more ideal than the oil pan."
 
Good shit. Interested to see how you install this and how it performs/what issues you might run into. Don't forget to plumb coolant to it for heating purposes, that will prove important to keep it from clogging up; needs to get nice and hot.
 
Enki said:
Good shit. Interested to see how you install this and how it performs/what issues you might run into. Don't forget to plumb coolant to it for heating purposes, that will prove important to keep it from clogging up; needs to get nice and hot.
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Yes, I know. I will use the connections intended for the throttle body.
 
I ordered one a week or so ago. Went to check on shipping and now Radium says it’s out of stock. Didn’t say anything when I ordered it. So I sent an email asking about when will it ship.
 
Radium responded that it would be back in stock in "2 to 3 weeks" and I thought, well, that sucks. Then a few hours later, I got an email indicating that it shipped. Yeah!
 
Did radium say anything about plugging the intake manifold port? I have a radium aos and originally I tried to keep the intake manifold port plumbed to the can using a check valve there and I think on the crankcase line? But it didn't work out.

I know radium recommends just plugging the intake manifold but then you read the damond motorsports blog and they advise against doing that. It's it really that bad of a situation to delete the intake manifold port and just use the intake?

Sent from my moto g stylus 5G (2022) using Tapatalk
 
The point of that port is to remove whatever gasses or fumes might be around the camshaft area; not sure if you're aware, but some of these gasses can wind up being corrosive, which ain't exactly good for aluminum.

Quick example from memory: If you remove the oxide layer from aluminum metal (you can keep this state permanently active via amalgamating it with elemental gallium or mercury), adding water to that mix will consume the aluminum and off-gas hydrogen. Pure hydrogen. The kind that explodes.
 
The port on the intake or the intake manifold? Everything I've seen vte goes through the intake including the valve cover.

BTW this is the blog post I was referencing where they do not recommend blocking off the intake manifold.


https://damondmotorsports.com/blogs/damond-blog/53965956-bye-bye-blow-by

Radium however seems to recommend blocking that off. Seems like if you want to still use it you're going to have to go with dual cans.
 
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Ah I misread. Using that intake manifold port means that outside of boost, you have a good source of vacuum to leverage. Inside boost, you'll need to use a port on the intake (preferably after the MAF).

You may not be able to use either vacuum port if your engine has too much blowby, however, as it can cause issues with the engine running properly. Not using it means your crankcase pressure won't ever be in vacuum, which is far from ideal.
 
Enki said:
Not using it means your crankcase pressure won't ever be in vacuum, which is far from ideal.
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Can you elaborate? Yeah, I know that a typical car PCV system puts some vacuum on the crankcase. But I had presumed that simply VTA would be good enough as far as the engine was concerned. Certainly not as good from an emissions standpoint. But I figured that the engine would be perfectly happy with simply VTA. Can you elaborate?
 
There's almost no vacuum in the intake tube when you're idling. So if you get rid of the intake manifold where there's a lot of vacuum at idle then there really won't be anything to assist in drawing out the crankcase pressure.

What will happen long term? I honestly have no idea which is why I ask since some aos recommend it.

Sent from my moto g stylus 5G (2022) using Tapatalk
 
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