Engine noise!

2003 C4S - 162k - oil change every 6k On the way home this evening, high pitch squeal could be heard driving about 30 mph - goes away temporarily with acceleration. Thought it may be belt/pulley. So belt taken off - still there but not as bad with the belt in place. I notice pool of oil in the throttle body - is this normal? Oil filler tube compressed at the crease - when engine is running - is this normal? very difficult to take off the oil filler cap while the engine is running. After couple of starts - started seeing white smoke on start only If i had to pin point the squeal - it sounds louder under the engine on the offside. Any pointers what it could be or what to check next?

AOS ?

Hi Poopga, AOS was my initial thought but I've never had one go so can't really comment. It makes sense though with the smoke and then oil where it isn't meant to be. I didn't know they made a noise when they go mind. It may well do though as it's the rubber diaphragm that tears so it might whistle. I'd happily take AOS over some other options. Good luck. :thumb:

I don't reckon its AOS. When they go its proper smog city as the engine pumps oil into the intake. A video or sound clip might help.......and a bit more definition on your description, e.g. Pool of oil.

From Pelican parts.. "In addition, you may hear a high-pitched squeal from the engine when it's running because air is being sucked in past the crankcase seal due to the extreme vacuum inside the case." https://www.pelicanparts.com/techar...Oil_Separator/09-ENGINE-Air_Oil_Separator.htm Sounds exactly the same sound and problem as this chap.... https://rennlist.com/forums/996-for...ossible-aos-failure-ideas-video-attached.html I meant pool of oil sitting at the back of the ipd plenum (not the throttle body!) enough to dip cover tip of my finger.

There's usually a small amount of oil sat in there but without seeing how much' its hard to be more specific. Personally, you'd know about a failed AOS......so would everyone else - proper smoke city.

On a Boxster when the aos fails ( there are different failures with these ) you can get a high pitched squeel .. its air being sucked in via anywhere the engine can .. release the oil filler cap engine running and if its dam hard to remove due to a vacuum then you have just proved its an aos. I dont remember seeing this on a 996 but i see no reason why not . As mentioned though a normal aos failure is an awfull lot of smoke out the exhaust . Edit Just to say you do get oil in the inlet mainifold as normal .. its how much YOU have and without pictures i cant say other than a rule of thumb .. if it pools each side then yes aos and belive it or not they dont always smoke .. again this is Boxsters and i have no idea why these are different to 996 .. but they are .

Thanks all. I couldn't remove the filler cap with the engine running. Lot more smoke this morning - but only on start up. Getting it picked up tomorrow to be taken to indy - hopeful it will turn out just the AOS and no damage to cat or anything else.

AOS faulty .. ill give it a 95% chance of being that .. i never say 100 %

When my AOS let go it went in spectaclular fashion, however there were symptoms for months just like the OP has described that I ignored, hoping they would go away. This sounds just like a failing AOS to me, and you should get it addressed ASAP. I nearly damaged the engine severely as several pints of oil were drawn into the inlet manifold when it went and it went into the cylinders, hydraulically locking the engine.

AOS Afternoon Can someone explaine the term AOS pls, PDCC4S

Air Oil Seperator Its a device that sits on the top left of the engine and is made out of black plastic. It takes the oil mist that is in the crank case when the engine is running and allows it to condense back into liquid oil and drain back into the crank case, whilst allowing the gasses into the inlet system to be burned in the cylinders for emissions reasons (its cleaner overall to burn them than allow them to escape into the atmosphere unburnt). The failure mode of these devices is the rubber diaphragm that sits inside thm perishes over time and after about 5-10 years they fail, allowing the liquid oil to be sucked into the inlet manifold. Lot of other bad stuff happens, but it's this that can really ruin your day, as the liquid oil can get into the cylinders in sufficient quatities to hydraulically lock them, and bend your con-rods.

Got my car back from eporsh today - it was the AOS!! All fixed and up and running again