The squeal from hell in a Porsche Boxter

I have a 2000 boxter with a tiptronic and 80k miles. I have maintained religously and the serpentine belt was replaced at about 75k. I am getting a high pitched squeal from the front of the engine on deceleration. Its not a belt squeal, but it sounds like a metal to metal or bearing squeal. My mechanic who has a lot of experience with porsches agrees. It does not do it when the engine is cold, only when its up to temp or has been driven 10-15 miles. It only squeals on deceleration. As soon as you touch the gas or load the engine it stops instantly. Most time if I just rev the engine a bit at a stoplight it will stop as well. We have had it on the rack twice. No leaks at all. The waterpump is tight and dry. All of the pulleys and idler show no signs of wear and spin freely without the slightest hint of noise or resistance. The belt looks good. The real puzzle is that in my experience once a bearing goes bad it will not come and go, but just keeps getting worse. There are no service bulletins that address this issue. I still believe it is a pulley or idler, but I don’t want to spend a fortune replacing all of them, especially if I turn out to be wrong. Has anyone else experienced this ? Any ideas ? Its driving us nuts. I can go to the shop but as soon as I touch the gas to put it on the rack, it stops squealing and the easter egg hunt is on. Help !!!

You say, “The belt looks good.” How old is the belt?

5,000 miles, 6 months

I only asked because I recently had an intermittent belt squeal on one of my cars. I checked the pulleys, tensioner, etc, and found nothing wrong. The belt looked fine, but was a few years old. Finally, when nothing else worked, I installed a new belt. No more squeal.

I don’t think this will work in your case, however, since your belt is practically new.

You might have better luck finding a Boxster owner that had the same problem on a Porsche forum.

I’ve heard of something similar - does the noise stop if you remove the oil filler cap ?

If it does it’s the Air / Oil Separator failing.

Don’t tell your mechanic you had to post your cars problem on Car Talk because he couldn’t fix it. These Porsche mechanics are a little sessitive about this kind of thing.

Same advice concerning the guys at the track,don’t tell them you even know the address of Car Talk. Do you know how bad it looks when your track buddies can’t help?..och

Spelling isn’t my high point either,isn’t that Boxster?

Yes, oldschool, you are correct about the spelling. My theory is that the car is offended because its owner can’t spell the name of the car that he owns, and the car is simply screaming out of frustration.


Seriously, however, I like Scudder’s theory about the air/oil separator, and I think that a bad PCV could be another possibility.

VDC - Porsche use an AOS instead of a PCV valve so yes you’re correct.

If it is the AOS then rlloyd needs to get it fixed quick, not only will it pollute the MAF and cause it to fail it has been known for enough oil to be dragged through the intake into the cylinders and cause catastrophic engine damage when the pistons tries to compress it.


I was not aware of the AOS previously, so you taught me something today.

If the AOS turns out to be the source of the problem, then I think it indicates that rlloyd’s mechanic does not have quite as much experience with Porsches as he should. It sounds like you could teach his mechanic a few things.

Couldn’t this problem also lead to oil leaks?

Not so sure about that, I only know about this problem from a Porsche specialist pal of mine in London, he had one of the catastrophic failures on his hands. The owner knew that by flooring it the squealing problem would stop temporarily and just floored it once too many times - blew the engine apart.

A Failing AOS won’t cause leaks but it will create vacuum in the engine since basically all crankcase air is being sucked into the inlet manifold. An easy check is if the oil filler cap is difficult to remove while the engine is running then the AOS is suspect.

WOW, I’m impressed. All due apoligies to the car guys for the typo. I have already apoligized to the car. It wasn’t happy, but I think were still OK. I can’t spell for crap. Anyway, I think the AOS diagnosis is dead on. It started squealing today and I tried to unscrew the oil filler cap. It was so tight I coudn’t get it off. I pulled out the dipstick and the noise stopped immediately. It was sucking air pretty badly and I could hear what sounded like a sucking gurgle even through the dipstick tube. I have ordered the part and will park it until I can fix it. I should have suspected something else, I also got a trouble code for the Oxygen sensor, but I swear it sounded just like metal rubbing metal. Makes sense now though. Thanks to all, I think this internet thing is here to stay. rlloyd

You ar eright, thanks.

Kudos to Scudder for nailing this one!
It really sounds like your diagnosis is spot-on!

I had the same problem on my 2000 Boxster with Tip. There have been a number of changes to the breather system since manufacture. My mechanic updated the entire breather system for roughly $650. Far less than the $XXXX.xx i was expecting thinking I had a torque converter failure!