AOS Issue?

Car - 2000 C2, 111K miles. Car sat for three weeks while I was out of town. On the way to work today, about 18 miles into the trip, I get a loud squeal from the engine compartment. Seems to go away at about 3000 rpm, but at idle or low rmp, its loud. Seems to get louder. At times, it was like air leaking out of a tire sort of squeal. Let the car sit until lunch. Crank it up after lunch, no noise at idle, but a huge puff of smoke out the passenger side exhaust. Thick, white burnt oil looking smoke. I'm thinking AOS issue. Anything else I should check before a run to the mechanic? Thanks.

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While the AOS may the cause of the symptoms that's not conclusive. Could be a bad water pump and the sound you hear is the belt squealing. This is hard to inspect with the car on the ground. There are checks you can do but really if you're not going to fix the car yourself, and I hope you do not have to tell your mechanic what is wrong, the best advice I can give is get the car flat bedded to your mechanic for his expert diagnosis. All you need check is that he has plenty of dark roast coffee to drink while you are waiting for the word on the car's condition. Bring extra pastry.

idle tensioner will squeal at low rpm and go away and higher rpm. White smoke is coolant or water being burnt off. Blue smoke is oil.

Thanks.

I agree it's not definitive, but your symptoms almost exactly match mine just before it failed. Do a search and you'll find some sound clips of the "falling whale" noise it makes.

On our Boxster some years ago, the AOS went bad. Someone showed me that if the AOS is failing, excessive vacuum is created in the sump, and the oil fill cap will have considerable suction if you try to remove it while the engine is running. Normally, it will come away easily.

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That was my experience with my Boxster's 1st bad AOS back in Feb. of 2004. With the engine idling, and not a real healthy idle either, I could unscrew the cap but could not remove the cap from the oil filler tube. The pressure diff created by the failing AOS was the reason. The 2nd AOS failure (the replacement AOS for the 1st AOS) I never bothered to test this again. Upon starting up smoke just billowed from the car's exhaust pipe and continued. After say 30 seconds it was clear the smoking was not just some residual oil in the intake so I shut off the engine and had the car flat bedded 90 miles away to a dealer and had the AOS replaced. I might note others have experienced a bad AOS but the cap 'test' didn't find the cap stuck. There are either 2 failure modes or the AOS fails and transitions through various symptoms.

I think that one of the things that people keep forgetting is that the AOS is an item that has a finite life, between 70k and 90k. After that, an AOS is simply in just in varying degrees of failure. They can fail subtly or catastrophically. For my money, I would plan on replacing the darn thing every 75k or so or certainly with every clutch change... If you have hit 100k, your AOS is past due for replacement and will fail sooner rather than later.

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Uh, my Boxster is at over 261K miles and on its original clutch. But your point is right up to a ummm point. My car's 1st AOS lasted until 80K miles. The 2nd lasted for around 100K miles. The 3rd one has I guess around 80K miles on it. Not going to replace it until I get some sign it needs replacing. In this particular case though the cause of the OP car's noise needs to be diagnosed and addressed. If it proves to be the AOS that's just dandy. But if it is not the AOS but assuming it is the AOS based on miles in this case could have the AOS replaced with the car returned to the owner with the problem that prompted bringing in the car still present. And if the owner leaves with a false sense of security if say it was the water pump serious collateral damage could result if the water pumped failed catastrophically. In the OP's case, if say the tech id's the water pump as the cause of the noise but the OP wants to replace the AOS at the same that's his call. But to walk in to his tech's shop and say "AOS" is not what I would advise the OP to do.

Follow up on my original post. Drove to my indie. As I pull in, the whine/noise/sound begins. My tech meets me at the car, says turn off your A/C, looks at the odometer, and says - That sound you hear is the failed separator. I'll check it out, but 95% of the time, thats the separator. So, separator replaced, and car is back to running great.

That ended well for you.

What did he charge you? FWIW on a Boxster such as Mr. McMasters, the AOS is much more easily accessed as the motor's installed backwards.....

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That's good news. BTW, the tech did what you wanted him to do. He id'd the the problem and fixed it. A tech at the car is worth 10 'net mechanics.

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Definitive proof that AOS failure sucks!

Yes, I'd like to know what he charged too, as I just replaced mine, pre-emptively, since I suspected it may have been the cause of a very small "oily" leak, which I suspected was perhaps oil vapor blow by. My lord in heaven, I never want to do that job again! The mkII engines hqve a different design AOS, which puts the friggin 5mm allen bolt right smack dab between the AOS, the intake runner, the fuel rail and injector wiring harness and then those squeeze clamps (and yes I own the right locking tool) were rotated and positioned such that the tool head for the clamp could not get to them! Fwiw, there is no reason to remove the alternator to access it like I kept reading. I did end up removing the expansion tank to get more maneuver room, and that was a whole nuther royal pita. It had already been replaced by an indie for the PO in '07, and it looks like he snapped a few of the plastic hose holders doing it, but I was able to use heavy duty tyraps to cinch everything back up. As it turns out the o-ring on the AOS had a tear in it, so maybe the cause. Haven't got it back together because I also replaced the water pump and Tstat and THAT is also turning into a different fiasco. That last bolt near the crank pulley, dear lord, I spent 2 solid hoirs futzing with ways to get it out oncce it was loose. Some of you guys must have pretty tiny hands that said they could just reach in an dundo it qith a socket. But thats another threar all together.