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Discussion summary
YOUR RESEARCHAOS is a wear item?
Reported repair
Replace two years ago
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Reported fix
FWIW, to fix a slight oil leak, I had the AOS rubber bellows (aka diaphram) replaced two years ago. Cost=$165 at dealer...problem solved.
Leading evidence: 'Replace two years ago' (1 discussions report resolution; 0 report an unsuccessful attempt). Across 1 matching discussions, the most frequently mentioned possible cause is 'quickly becoming a diy'er' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Replace two years ago' (1 discussions). For that action, 1 discussions report a resolution and 0 report an unsuccessful attempt. The most frequently reported fix is 'Replace two years ago', supported by resolution reports in 1 discussions. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
I had my clutch replaced and then 8 months later had to have my AOS replaced.
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Suggestion
Have you thoroughly cleaned the underside of your car yet?
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Suggestion
well the AOS failure could mean the end of the whole repair game period.
Replace aos - inexpensive preventative, the car had 75k
No successful repair reported for this finding.
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Suggestion
As for the AOS, I learned enough about that to bring a new AOS with me and didn't ask the dealer, I simply said, while the trans is out replace the AOS - inexpensive preventative, the car had 75k on the clock at the time.
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Suggestion
I asked about replacing my motor mounts when the dealer was doing the clutch and the IMSB - the mechanic said no, better to wait until the water pump is replaced.
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26 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Generation: 20261026T094842Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Is the AOS considered a wear item?
I know some folks recommend changing it out if you're in there doing something already, but is it a wear item like say, a water pump, or bearing? Or does it just decide to "break" one day?
If you overfill or go crazy at the track, then you can potentially damage your AOS. This won't matter if the AOS has 60k or 1k miles on it.
Everything in the engine is a wear item if you drive the car long enough.
While the AOS is not an officially recognized wear item, compared to say tires, brakes, clutch, etc., it does wear out or more likely suffers from material fatigue and fail.
If you are "there" and the AOS has some miles (>50K?) replacing it might be prudent. But I've gotten double 50K miles from AOSs and I'm never "there" so I just wait for signs the thing needs replacing.
Overfilling the engine with oil afaik has no effect on the AOS and its longevity. Overfilling the engine with oil is something to be avoided though. In fact whether you do your own oil/filter service of have it done there is no excuse to end up with the engine overfilled with oil.
On the track the engine can emit copious amounts of oil smoke at times. This arises from oil vapor overwhelming the AOS under certain extreme temp/high rev and high g-force situations and being routed to the intake where it then goes into the engine and is burned.
The efficiency of the AOS, the freshness of the oil, the type of oil, how much oil is in the engine, among other things play a role in this not happening at all or very rarely or happening and if it happens how severe, mainly how "bad" it looks.
As is the case on the street, if this smoking happens frequently on the track it can be a sign the AOS is on its way out.
^^^ Same response I got recently when I had the clutch done on my car. I told them I wanted to replace it while they were in there and my shop talked me out of it since it looked fine and showed no signs of being on it's way out, even though it had 100k miles on it.
Sorry to tell you but that is very poor advice. The AOS will fail eventually. The rubber gasket inside as well as the plastic housing itself ages and will crack. The cost to replace it while you are dong this clutch is a fraction of what it costs to do independently. At 100k, your AOS is ripe for failure. They can fail as early as 70-80k...
Don't really think doing the clutch is really "in there" as far as AOS replacement is concerned, but I have to agree; a 10 year old rubber diaphram constantly exposed to heat, rubber, oil vapor and coolant for 100,000 miles and it's days are severely numbered. While it sure appears that no permanent engine damage occurs when it fails, it sure does make one helluva mess of the intakes, runners, valves, etc and can't be good for your cats. But if you can just drop your car off anytime and have the dealer or indy do it, and are ok with that then I guess it doesn't matter. Me, I'd rather handle it on my own terms.
AOS typically fail from the inside out. Most expansion tanks look fine even when they go. These are wear items, especially when a lot of these cars are getting 10 years old. Mine went at 34k miles on its 2nd day at the track. A real pain to do if the engine is in the car. I am replacing the AOS when I do IMS bearing install. A lot easier to do with the engine out.
I had my clutch replaced and then 8 months later had to have my AOS replaced. It started leaking water. I wish I would have replaced it when I got the clutch done. The labor was painful.
The AOS is a wear part simular to the IMSB in that is marginally robust enough for what it is designed to do. In the case of severe use or defered maintenance your mileage will vary. If the AOS ingests enough oil to hydrolock a cylinder it's time for a new engine.
Except when it hydrolocks your motor. Just ask the guys racing them in Grand Am's early GS class. Porsche Motorsports developed the expensive ($600?) dual chamber AOS to solve the hydrolock that was occuring. If you have the trans out for any reason just drop the motor a few inches and change out the stupid AOS. It's a $110. part....
of course they don't want you to do any preventive maintenance..
guess who will benefit from seeing you again !
I had the same issue with my porsche dealer... 'dont' replace if it is not broken'
They would not even want to replace the thermostat when I changed the water pump !
I mean really they would not want to do it !
It was so annoying talking to them, I actually let it go... shameless sales strategy if you ask me
well the AOS failure could mean the end of the whole repair game period. Engine kaput...
Not too smart if you want to ge first dibs on that new suspension job.
I asked about replacing my motor mounts when the dealer was doing the clutch and the IMSB - the mechanic said no, better to wait until the water pump is replaced. I remember looking in the engine bay and clearly seeing the easy access to the right hand mount, wish I would had been a bit more persistent. I am sure the mechanic was simply calculating his future labor dollars.
As for the AOS, I learned enough about that to bring a new AOS with me and didn't ask the dealer, I simply said, while the trans is out replace the AOS - inexpensive preventative, the car had 75k on the clock at the time.
Good inputs but I still trust my Indy tech. He probably did not see a need since my car is under 60k.
He did say that it would start smoking badly and it was even ok to drive it to the shop smoking. Is he wrong about that?
Steve, you can trust but verify. These guys are in it to make money. They may suspect your quickly becoming a DIY'er. As much as you like your car, you will enjoy the "together" time from the DIY projects. Have you thoroughly cleaned the underside of your car yet? Im detailing the chassis/suspension parts as I have time. You would be surprised at what you can learn under there.
If the AOS goes south dont drive it smoking. You will damage the 996's rep. Just replace the AOS. I know you got the tools.
Replacing the AOS on the MKIIs is a total bitch, if you don't drop the engine, and not for the faint of heart. Motor mounts and waterpump are a walk in the park compared.
Try changing one out on a C4 Tiptronic. Everyone, including Porsche, said it couldn't be done without dropping the engine or trans, but I have the scars to prove that it can!
Cheers,
TomF
I talked to an Indy recently about doing the AOS while "in there" and they said their AOS service is to replace the bellows. Is there more to changing out the AOS than this?
Change the whole AOS. It's got lines attached to coolant and such at the top and 2 bolts holding the AOS in. The bellow is at the bottom. Replace the whole unit while you are there. I got my first AOS replaced at 102k...was leaking oil and coolant. It's leaking again at 148k...I'll be replacing it again as I need to drop the tranny to replace the tranny mount.
