tscribner

Recently had my AOS fail creating a huge cloud of white smoke. Looked like I was killing mosquitoes. Lost about 2/3 quart in 1/4 mile - I was almost home.
After replacement, rather easy but still took me 3+ hours - mainly to get the side connection loose, I disected the AOS device.
Inside the vertical round part on the top is an elastomeric diaphragm that failed.
I don't know the type of elastomer that Porsche selected for this service (I will get it shot via FTIR to at least verify the family and report back someday) but it was chemically attacked and was torn in three places. Hardness of the center, thicker part of the diaphragm was Durometer A 65.
The black plastic cover is vented to the atmosphere via a tiny hole at the very bottom edge of the cover as mounted in the car.
The diaphram acts as a pressure regulator to limit how hard the engine "sucks" on the vapor portion of the engine. When the diaphragm fails, it puts full engine suction on the crankcase.
Attached are some photos showing the layout and a close up showing the degradation of the elastomer. There was nil attack on the elastomer on the air - atmospheric - side. All attack was from the oil side.

Tony
2001 Boxster without the S

Macster

I cut one of my failed AOS's apart. The canvas/rubber (well, something like rubber) diaphragm had a crack in it that I believe arose from simpy mechanical failure, from the diaphragm simply wearing out over time. IOWs, material fatique.

Happened at around 80K miles.

Sincerely,

Macster.

Byprodriver

My 2000 S original AOS gradually failed @ 82,K miles soon after the oem waterpump shaft. In the last 12,K miles I am on my 3rd AOS. Mac does the OP's AOS diaphragm appear to be the same material as what you saw in yours?

Macster

The diaphragm material in the AOS I cut apart appears to have a shinier surface, appears to to be made of a more plastic type of material.

I didn't cut apart the factory AOS that came with the car. The AOS I cut apart was its replacement, after of course it failed.

Sincerely,

Macster.

LoveMyCayenne

I am having the same problem with my 04 Cayenne Turbo. The AOS separator has a tear in it which is causing the smoke. My issue is that in order to get a new diaphragm, I have to buy an entire valve cover assembly which is like $600...does anyone know if I can obtain JUST the diaphragm? Thanks in advance for the help!

Macster

My WAG is that the diaphragm is not available separately.

One way to tell is if you can see or examine the AOS and note if it appears to be bolted/fastened together. The ones I've seen -- which does *not* include any for the Cayenne -- are made of plastic and are fused/glued together and are not servicable.

A sanity check would be if the parts department computer at your local Porsche dealership doesn't show the diaphragm as a separate item then you are stuck buying the complete assembly.

Regardless, were I you I'd not drive the vehicle too much in its condition. There's the chance the engine can ingest enough oil to suffer from hydraulic lock and if it does this the engine can suffer severe maybe even fatal harm.

Sincerely,

Macster.

sjfehr

I have to wonder if the engine would still run just fine, were the AOS to be completely disabled and replaced with a plug on the vacuum side and an open tube to vent the crankcase to the atmosphere.

Macster

Maybe. For a while.

The engine would likely develop leaks since it would run at most of the time at a pressure higher than it operates at when the AOS is working properly. This would tend to force oil from around the seals and some gaskets.

Additionally, unburned gas and water vapor would be less likely to be removed for 2 reasons. One is with the crankcase under more pressure the boiling point of these fluids is raised and the oil may not get hot enough to turn these fluids into vapor once again.

And the 2nd reason is even if the oil did heat them to vapor the vapor would not be as thoroughly removed since there is no real ventilation of the crankcase.

The oil would build up unburned gas and water and these would of course contribute to the formation of acids and sludge. The oil's anti-corrosion and detergent additive packages would be shorter lived than they are now. More frequent oil/filter services would be required.

Besides the car would stink. I can remember years ago when the only engine crankcase vent system was a road draft tube and to be behind a car and to smell the fumes wafting from the vent tube... Yuck.

Sincerely,

Macster.