More stupid AOS talk...
 

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. :confused:

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.

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!

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! :eek:
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.

" 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.

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/

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.

https://lh3.googleusercontent.com/-m...o/s800/AOS.jpg

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

AOS hack/upgrade Stelan's mod
 

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.

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

Like this?
https://lh3.googleusercontent.com/-m...s800/AOSv1.jpg

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

http://986forum.com/forums/uploads02...1465425156.jpg

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

Thats awesome Stelan.

All thats left is to make a Parts list with source links and you have a full DIY article.

Not sure that pictures would add too much more info except perhaps the location and how the can was fixed in place.

Parts List with numbers and sources for Stelan AOS
 

1. The PCV is from a 2003 VW Passat 1.8l turbo(??)
The generic part is BECK/ARNLEY 0450392 from Rock Auto $23 minus their usual 5% discount.
2003 VOLKSWAGEN PASSAT 1.8L L4 Turbocharged PCV (Positive Crankcase Ventilation) Valve | RockAuto
2. the 'catch can' - I am assuming that a generic EBay can 500 to 750ml & made of aluminum is the best choice. A design with an un-screwable cap is easiest for fabrication? Most have inconveniently positioned fittings that require modification or plugging:
Universal Silver Round Aluminum Racing Oil Catch Tank Can | eBay
The Mishimoto & Moroso cans seem too expensive for an experiment?
3.The various barbed fittings : - I prefer using brass & source from "Fast Fittings" because I can usually find everything I need on their site:
https://fastfittings.com/
For this application, here is a good place to start because it gives the actual(not just nominal dimensions of the fittings:
https://fastfittings.com/collections/brass-hose-barb-fittings

4.The stainless steel wool (coarse) is here in abundance & made in USA!
1 lb Stainless Steel Wool Roll Coarse Great Forexhaust Muffler Repacking | eBay

What we also need is a specification and source for the absolute best vacuum lines - both the hard line and the softer grade.The OEM items usually become brittle.Any improved AOS is only as good as the next weak link!
I prefer to avoid using what is described merely as "plastic" tube and try to find a specific high performance polymer to avoid deterioration and leaks in future.Tygon tube i one candidate ? I tried finding something better than SAE J30R7. 30R9 is too stiff & thick?
I hope this info and some of the ideas help move this project along for others who will follow.

So now we need a track rat who's willing to build this and try it out! :eek:

I'm still apprehensive because if something as simple & inexpensive as Stelan's AOS is effective ,why didn't Porsche do it this way? And why haven't other talented enthusiasts done this years ago?
Some other mad guy proposed a system with an electric vacuum pump but that was way more complicated than Stelan's AOS.

Hello,

does anybody know the inner diameter of the vacuum lines needed?

In general these hoses have to be fuel and oil resistant. So i would think more something like fabric reinforced fuel lines. Also had the idea of silicone lines, but silicone seems not to be oil and fuel stable. Also it has to be ethanol stable.

Regards, Markus

Great suggestion Markus.
Silicone hose in the larger diameters for connection to a pcv tends to collapse when warm and under high vacuum at idle.Bends will kink. For that reason it will fail the Smog Test here if a tech sees the vivid color of aftermarket silicone hose.

You are correct, here is a fiber wall reinforced version but that helps with pressure ,not vacuum.
One solution may be to select thick wall/heavy wall silicone.It is so much easier to work with than the stock "plastic". I found some with a 3mm i.d. and 8mm o.d. Turbosmart TS-HV0303-BK
3m Pack-6mm Vacuum Tube Reinforced - Black
Normal wall thickness would be 1.5mm.This item is 2.5mm.Should help??
One complication is that silicone is very elastic so you usually buy it 1mm smaller i.d. than the 'plastic' OEM style tube.
Note that the silicone hose manufacturers seldom specify a wall thickness and tend to use hyperbole like "turbo" ,'platinum cured' ,so it can be difficult to find a truly premium product.

Only problem is that the AOS unit uses "click on" hose ends which are vastly more failure prone than the hose itself:

http://www.pelicanparts.com/techarti...mall/Pic37.jpg

Hello Gelbster, hello JFP in PA,

JFP in PA: thanks for adding the picture. Pictures say more than words. ;)

In general it seems that the AOS component (diaphragm) and the connectors seems to fail. The rest of the system seems to be stable. Rubber hoses will always fail if they transport oil. It's just a matter of time and quality and heat cycles.

First, i'm not a engineer, but maybe some aspects we should consider – also a summary of the aspects you have given to the discussion (hope i didn't miss something).

• The hoses have a defined diameter. That means they have a defined maximum flow capacity.

• If the hoses are too stiff that can lead to problems caused by vibrations. Especially when the AOS / catch can is mounted to the car chassis.

• If the hoses are too elastic they may collapse by underpressure.

• The special connectors can be a problem. I don't know if the connector at the throttle can be replaced – never changed an AOS at the 096 myself.

• The hoses must be oil resistant and to some level they should be fuel and ethanol resistant. i don't think fuel and ethanol will be a main problem, because in general the fuel / ethanol part in motor oil is low. But old oil can contain aggressive substances, even if it is full synthetic.

• We need to define how tong the complete system should work without failing.

I would say if the AOS system works for 15 years without failing it will be OK. What do you think?

Mostly the aspect with Porsche classic parts is that they are expensive because they are Porsche classic parts; not because they are expensive to make.

So i did a research on both hoses and connectors and AOS. There are 2 hoses that lead to the AOS housing and it seems that they both have these special connectors on both ends. Also they differ from model year and in part numbers. So it looks like Porsche has improved the parts and you should always look for the newest version. Also the lines differs from model to model, so there might be problems to offer an one fit all solution.

AOS: 4 different versions:
- 97 A 996 107 023 51
- 98 A 996 107 023 01
- 99 A 996 107 023 04
-> 03 A 996 107 026 01

Part number 4 (hose):
Until 2002 (DE): A 996 107 147 53, A 996 107 147 54, A 996 107 147 55
From 2003 (DE): A 996 107 147 58

Part number 5 (hose):
Until M 65x 01419 (DE) 996 107 145 06 (M96.20)
Since M 65X 01420 (DE) 996 107 145 06 (M96.20)
M96.21/22 / M 96.23/24 996 107 145 06

The hoses themselves are not ultra expensive. At Amazon they are around 40-70 USD. Which is a lot of money, but not ultra overpriced for Porsche parts. And i think you could get them cheaper elsewhere.

So where to go from here? Honestly i don’t know. I don’t know if the parts are really different in detail. If they are, this will be a bigger puzzle than i thought first.

What do you guys think?

Thanks & regards, Markus

http://986forum.com/forums/uploads02...1466201595.jpg

Big advantage of the Stelan AOS is that many of these issues are eliminated because the stock AOS ,problematic connectors/fittings are eliminated or generic items substituted in brass(not plastic)

How does he resolve the click on fitting that is molded into the plastic intake behind the throttle body?

Maybe increase the hose diameter to go around it & get clamped in place. The connecting tube is 26mm diameter with a 28mm "barb".

Increasing hose diameter may reduce the vacum signal enough to effect ring seal though.

I wonder why the 97 AOS with the horozontaly oriented diaphram was replaced with the vertically oriented diaphram?

Because oil used to sit on the diaphragm, weakening it with time.

yes hose diameter is larger and it clamps over the fitting, the clicker is the part that is removed the part left is great for having a hose and clamp as it has a barbed-shape fitting.

hoses that are design for air/oil will outlast the brittle plastic ones, and yes those click on connectors work great for years then they are very problematic once hard plastic starts to degrade.

Just saw this thread, brilliant idea from Stelan, a new-must for the corner-heavy track I'm assuming.

@Markus - the material you are looking for is called composite for hydrocarbons. "Composite Hose for Hydrocarbon" (Schlauch für Kohlenwasserstoff) for instance should return data from your nearest hardware supplier.

stelan, if you are still out there, can you please give us a longterm review of your setup.

1. Has it been holding up?
2. Any thing fail or brake down since?
3. Has it resolved all AOS issues since?
4. Any relevant comments on this?

got an AOS failure and about to start tracking the boxster. Im stuck between starting the endless AOS replacement cycle or buying a motorsports AOS for a brick of gold.

On the other hand, your setup might just resolve all of this.



Thanks,

Chris

From what I understand, the design had a fatal flaw. Stelan seems to have taken $200 deposits from people in Nov. 2016, then just disappeared. It's been 2.5 years since anyone has heard from him.

He was a good guy, so it really makes me wonder what happened...

I believe i found a catch can setup that will work well and it should be less than 100 bucks. It basically sits in line between the aos and the intake.

Interested!
Pics?

Sent from my SM-G970U using Tapatalk

https://www.amazon.com/Moroso-85486-Separator-Mustang-4-6L/dp/B006JZ97EU

that is the unit, prices have come up a bit, but with coupon codes at jegs/summit, shouldn't be bad.

The mounting bracket has a single hole. Remove the ground strap nut, slide the bracket on, retighten nut. Its a tight fit to the forward passenger tab for the engine cover but it'll go.

Will take some pics later this weekend, but with the exception of 2 angled reducer fittings from home depot, its basically plug and play.

some good recent threads on the rennlist 996 forum on this. basically, if you replace the aos with a catchcan (or an aos with a higher-flow diaphragm) then you introduce too much crankcase vapour during high vacuum idle situations (ie when you come off throttle after wot) and screw up idle fuel trims.

if you put a catch can after the aos then it has to be of sufficient size/volume to make a difference should the aos fail.

one solution that seems to be effective is to vent the aos to the airbox. i have yet to research it to any degree (i am of the 'just use the most recent version of the aos and you will be fine' school) but apparently it doesnt foul the air filter too much, and the airbox is of sufficient volume to hold the oil should the aos puke up. not certain if there is sufficient vacuum at this location to positively vent the crankcase, or if this vacuum is even necessary.