More stupid AOS talk... - 986 Forum - The Community for Porsche Boxster & Cayman Owners

So this week I changed out my AOS (again) because last week I had a smoke bomb/flashing CEL at the track. The motor-sport AOS is on my wish list and probably, if I could make the proper decisions, I could have spent less and solved my problem. So, I cut open the old AOS which had been pumping oil through my intake and causing mayhem, only to find that the diaphragm was like new, no other obvious physical problems whatsoever. Okay, on the track I'm fairly new (2nd season), I'm running street tires (Mich sport PS2s), I'm not pulling big lateral G's on the corners as if I were on sticky R comps. Is the stock AOS really that bad??? Question: How many of you share this experience, pulling off the hose between the AOS and the intake plenum, to find it bathed in oil? I've got a sport oil sump baffle coming in from Pelican next week with some other necessities and am hoping it will help! I've heard talk about a catch can, but the jury seems to be still out. Talk to me.

Assuming that your AOS is working (max of 5 inches or water steady vacuum at the oil filler cap), you are always going to find the hose from the AOS to the intake coated in oil, that is simply a fact of life. Adding a catch can will only coat that as well. The AOS is designed to reduce the amount of liquid oil pulled into the intake system, but not to eliminate it completely. The problem is that oil is being transferred as vapor when the engine is running hot, and that vapor accumulates on everything it touches. That also happens with the motor sport version as well. If you are smoking badly at the track, and the AOS is working properly, the problem lies elsewhere, as in the AOS system pulling liquid oil out of the cam covers.

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How does this happen? p.s. It's not smoking badly. This is only the second time that it has happened.

I've had the extreme smoke bomb action on my '02 at the track recently as well. I've ordered a new AOS, special oil pan baffles, and "deep sump" kit to lower the oil pan 1/4". Based on what I've read, that commonly solves the problem. I'm really hoping it does!

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At speed, your cam covers have a lot of oil in them; add G=loads in corners and some of that liquid oil can get sucked into the AOS system (which has a vacuum line running to each cam cover). While the AOS can handle some level of liquid oil, it cannot deal with a flood, and more than normal vapor gets sucked into the intake. Porsche had been aware of this for a long time, and actually produced an exotic and hyper expensive kit (read $10K+) for the heavily tracked 996's to help limit it. Amongst other things, the kit contains a "north west passage" oil recovery system which consists of additional oil scavenging pumps in the cylinder heads with lines to run the oil back to the sump. Unfortunately, this kit was never made available to fit in a Boxster.

And, unfortunately, I don't have a spare $10K+ even if it were available! Oh, and thanks for that explanation!

Suggest you read up threads about installing the deep sump and baffles. If you put the horizontal plate-baffle in the wrong place, if the 'windows' jam open ,if the pick-up tubes aren't the right ones - it will be sub-optimal. It seems the cheaper sump spacer+baffle kits work but only with intelligent fitting & fiddling . The deep sump kits (Mantis/Brey Krause?) seem to work better out-of-the-box. Need to check your vac system too. An inexpensive paint-can smoker works well.

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" Adding a catch can will only coat that as well." I had hoped that someone(Stelan?) would publish a diy catch can solution by placing a Catch Can ahead of the AOS to divert liquid oil direct to the sump. From what JFP and Porsche R&D have discovered it seems unlikely that a cheap,simple catch can would be effective? see post #8 in this link to a previous discussion: http://986forum.com/forums/general-discussions/60203-new-aos-failing.html So time to investigate other contributory factors like lack of anti-foam additives in the engine oil?

Problem is that the AOS system draws vacuum on both cam covers and thereby the sump. Even at only 5 inches of water, hot oil is going to give off some level of oil vapor, as well as other vapors (we will get back to that in a moment). To limit the vapor transmission to the intake hose (read vacuum source), the catch can device needs to be cooled to condense this vapor back to a liquid. This presents a couple of issues: Where to put the two devices (one of each bank, otherwise you would need one larger unit), how to cool them and keep them cool in proximity to a hot engine, and how to get the condensed vapor separated (some of it is oil, some is water, some is fuel) so that only the oil portion is returned to the sump. You would also need to figure out how to dispose of the non oil components from the cans as well because you do not want them returning to the oil system. (currently, they are sucked as vapor into the intake and burned). Add in conditions where there is an overly large amount of liquid oil being thrown about the inside of the cam covers (high RPM and g loads in the corners at the track), and now you have some liquid oil entering the catch can system as well. This also has to be handled at the separation stage. None of this is insurmountable, but it would take some very intricate engineering (read expensive) to make it all work.

AOS units simply are not lasting these days. The latest run from Mann has proven to have issues, as I have experienced them several times in the last couple of months. We've been testing a product for a while thats almost far enough along to pitch to distributors. If they accept it, the AOS problems will be over.

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Hello Jake, Sounds very interesting, are you talking about a new AOS design, or new internals for the existing AOS..? Regards, Gilles

Good luck with the new product Jake ! I am surprised a diy system using a small,brushless 12v vac pump + adjustable pcv+catch can +check valve has not been tried. That would allow an AOS delete. Some hot rod/race guys do this. http://www.hobbyexpress.com/power_25_bl_outrunner_motor_1250kv_1036351_prd1.ht m http://grannys.tripod.com/evac.html http://mewagner.com/

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I will try to get the time to write a good diy on my custom AOS I have been all over the place due to work but will try to find the time Steve

Steve, You also squandered time restyling the Boxster into something far better looking and more functional that Dr. O did ! So you are forgiven for neglecting te AOS hack write-up :-). As you can see there is great interest in your system !

Also looking forward to Stelans DIY. Would a sketch be worth a thousand words? Your verbal description sounded pretty good. I understand you are short on time so to help I have sketched what we think you built from the description and you can correct and fill in any missing details. Could you folks submit corrections, clarifications and Pics and I will improve this 1st draft drawing. Particularly pics/drawings of what the lines connect to and material sources.

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Please let it be yes, if you want an additional tester I volunteer

Great dwg ! Suggest the vac port is moved to the top of the 'catch can' + a dip tube inside.This may avoid sucking condensed oil/fuel vapors into the inlet? That is the conventional catch can arrangement. Mounting the new can as high as possible may also help drainage and avoid it getting swamped with liquid oil? IMHO this drawing is worth using as the basis for a new AOS-mod thread.

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So the Middle port on the bottom should move to the top and have a "Dip Tube"? Like this?

Here you go, sorry about the missinformation as the pcv is not from a vr6 but a 1.8turbo vw. vr6 one will work but the 1.8t is a little lower profile and has only two ports also there are a couple of things I do not remember exactly like the size of the barbed fitting that I use with orings and rtv into the small engine block oil return, perhaps if someone does this we can update some of those details in the drawing, all 3 ports where there are oil vapors need to be at the bottom, so all fumes go thru the ss media and condense oil into liquid to be returned back to the block, on top it should only be the pcv port with clean air/vapors this drawing also includes a coouple of corrections and changes as the large hose is actually not 1" but a little larger in diameter and as not everybody has access to a lathe turn the small fitting is updated with a double barbed fitting, also this shows the bulkhead bottom fittings with nuts and rubber washers ahas not every one has a tig welder to weld bungs

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thanks, I get very little time of fun due to traveling so much but I will soon retire and have fun full time, lol