944 Lachlan

it seems to me that the AOS is basically a catch can, with the added bonus that it returns the oil to the crank case. Only down side is it doesn't filter the air too well before it gets returned. Has anyone contemplated putting some filter media in the AOS to turn it into a catch can?

Dougs951S

I think that'd be a bad idea, with the potential of getting said media in the crankcase/oil.

V2Rocket

The AOS is not a catch can...it is a "cyclonic separator" intended to remove heavier/larger oil drops from the air in the crankcase.

The lighter oil vapor and "free air" (including combustion event blowby) is then routed into the intake tract, before the throttle body, to be burned to clean up the engine's hydrocarbon emissions.

It works very well for having no moving parts, or really anything inside the can.

People have put copper/stainless scouring pads (from the dish washing section of Walmart or wherever) into the "can" to try and trap more oil but I don't see the point.

Better to fit an actual catch can between the AOS and intake, if you have that much oil in the intake.

Van

The point of a catch can is to *not* have the oily air circulate back into the intake manifold and thus into the combustion chamber.

Tiger03447

+1 on what Van and Spencer said..
If a vented catch can were used, it would be important to have it positioned BEFORE the MAF so there wouldn't be a vacuum leak and unmetered air going into the intake system. If the can were sealed then it could be placed anywhere in the system to help keep the intake manifold clean. Correct me if I'm wrong here. Comments please. Thanks.

944 Lachlan

Right. And the AOS does a poor job of it.

Yes, I have that much blow by and yes, I need a catch can, but I don't see the point of having an AOS AND a catch can. I thought maybe if you could put some more filter media in the AOS you could have both in one. But I see your point that you wouldn't want to risk that going into the crankcase.

V2Rocket

The catch can "catches" the medium-weight droplets that the AOS misses...doesn't hurt to add the can in between.

993944S2

Why do you have that much blow by?

944 Lachlan

I'm guessing it's the 30-year-old rings