Having trouble visualizing this. The AOS connects behind the throttle plate, which is way downstream of the air box. I would think that in case of an AOS failure, oil would get sucked into the intake manifolds. How did the oil find its way all the way back to the air box?

Jake,
Does running the oil level down one notch (from MAX), helps the AOS or not ..?

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250k plus miles, i think his car has the highest mileage of any on the forum.

No, the AOS is not immersed in oil, despite oil level the operating conditions for the AOS are the same. It is constantly exposed to oil mist and vapors on one side and manifold vacuum on the other.

Not changing your oil frequently enough (not just mileage, but time) is a huge factor in this equation as well as the oil thats used. When chlorinated paraffin is included in the composition of an oil, the AOS hates it.

On top of that, the AOS is a low quality product and always has been. If it wasn't an emissions component I would have released our version long ago.

Imagine about ½ quart of oil in the intake runners and cross over tubes. As the Jägermobile is put on an incline going onto the tow truck, the oil starts flowing back into the throttle body (valve closed so the oil backs-up there for a bit) and then into the main intake tube. As the tow truck levels the flatbed the oil then starts flowing past the MAF sensor and into the air box. There is a drain valve at the bottom of the air box with two disk filters; the oil slowly flows through those filters and onto the flatbed.

http://986forum.com/forums/uploads01...1396196203.jpg

Goldberg would be impressed.

I have seen a picture of an odometer with over 300,000 miles from someone in Florida.

Mandatory! AOS is the only maintenance item I have left on my list. Maybe this year.

Jager what were your symptons? Big cloud of smoke?

Jake, I change my oil more often than average, between 3500 and 4000 miles. I am at the coast and driving along elevations that vary between 50 and 200 feet above sea level. What oils contain chlorinated paraffin, or should I ask what qualified oils don't have chlorinated paraffin? Thanks

I noticed a little hesitation going up a hill, as it leveled at the top of the hill there seem to be a few miss-fires, I looked at my dash for CEL and there were none. Then I looked in my rear view I noticed a fog of smoke behind me. I slowed-down and pulled into the right lane and off on the next exit. As I pulled into the Mobile station (one I frequent quite often) there was an impressive amount smoke coming out of the tail pipe (a little scary at the time). But it didn't take long for me to realize it was probably the AOS.

Because they have to admit the Yanks have a better, non-engine-endangering system. Porsche's is not even a good execution...

FloridaBill.

still on the original IMS. BUT...he drives the car heavily (does not let it sit) and maintains strict dealer service. I recall he fired his dealer service dept because the new mechanic did not pass muster on the telephone test of "how closely to you follow the letter of service manual" on spark plugs.

I'm still trying to figure out the function of the AOS. Isn't it roughly equivalent in function to an old-fashioned PCV valve?

Yes like a pcv but because the motor is a flat 6 it has a harder time controlling the oil vapors. Its also different from a pcv in that the porsche uses a close crankcase system with no vent. So in instances where a motor has more blowby and higher load it tends to force the blowby back into the intake.

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Just out of curiosity do you do a lot of engine braking? I wonder if that has an effect on the aos?

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In that case...what does Subaru do? They're the only other flat boxer motors being built today IIUC.

Other cars I've worked on have two vents. One is the PCV valve connecting the crankcase to the intake manifold on the engine side of the throttle plate. The other is a plain tube vent (perhaps with a flow restrictor) connecting the crankcase to the intake plumbing between the MAF sensor and the throttle plate. Is the AOS a combination of these two functions? :confused:

Doesn't running with the oil level a bit too full also contribute to this?

I can see chronically extended oil service intervals being a factor, but atmospheric pressure at sea level causing repeated AOS failures?? That seems a bit of a stretch.

I sure wouldn't change this as a pm item unless I had a clear indication that the existing one was failing. It's just as likely that a new one could fail before the old one would have, and I have seen in other threads that there is apparently a fair number of them that come defective right off the shelf. Don't fix what ain't broke.

No, I very rarely down-shift and use the engine to brake.

Absolutely not. Manifold vacuum is heavily dependent upon atmospheric conditions and thats what gives the diaphragms inside the AOS their biggest workout.

Before the AOS failure was well known we'd always receive cars with this failure that were thought to have "blown engines" from areas near sea level with California and Florida always having the most, along with the entire east coast. We receive calls and keep logs from all over the USA, its not like we only see local cars, and in fact its quite opposite as we have Porsches here from 30 states now and only one of them is from our own state.

I've never had an AOS failure called in from Denver or any other area of higher elevation. When I travel across the US to instruct my Porsche engine schools I quiz the attendees on several things and one of those is "Who here has seen an AOS failure?". The trend data I have gathered has been priceless.

BTW- Suby engines also have AOS issues, especially those with high boost as the changeovers from + to - manifold pressures are hell on them.

Well that's good to know...for me personally. Boise is at about 2,700 ft elevation. It's the lowest point in the area, with the roads over the Rockies quickly getting to above 5,000 ft. Highest pass likely to see here is Galena Pass on Hwy. 75 at 8,900 ft.