Air Oil Seperator - Boxster 2.7 1999

[justinbaker]

Hello all,

My air oil seperator is failing, or failed. I have a vacuum on trying to remove the cap when idling, flickering oil light at idle and strange squeeking noises.

I have read there have been some revisions to this unit.

Firstly, where is best for a replacement, and if so, do I buy the upgraded version?
If the upgraded version is the best option, what additional parts will I need. Piping tubing etc?

[bertelli_1]

Justin,

The seperator won't give you poor oil pressure or strange noises (apart from an air leak whoosh - if you can hear it). A decent vacuum at the oil filler would also suggest it is ok. I suspect you have a far more serious problem I'm afraid.

btw - all seperators supplied by porsche are the updated type.

[Rockster]

justinbaker said:

Hello all,

My air oil seperator is failing, or failed. I have a vacuum on trying to remove the cap when idling, flickering oil light at idle and strange squeeking noises.

I have read there have been some revisions to this unit.

Firstly, where is best for a replacement, and if so, do I buy the upgraded version?
If the upgraded version is the best option, what additional parts will I need. Piping tubing etc?

My local Porsche dealer parts department manager tells me parts are keyed to a car's VIN.

Visit your local dealer parts department and supply a VIN and find out what the latest AOS part number is.

AFAIK, there is no best. There is at best, better. My 02 Boxster is on its 2nd replacement AOS. 'course, the 3 AOS's have been spread over 247K miles of driving...

Sincerely,

Rockster.

[Rockster]

bertelli_1 said:

Justin,

The seperator won't give you poor oil pressure or strange noises (apart from an air leak whoosh - if you can hear it). A decent vacuum at the oil filler would also suggest it is ok. I suspect you have a far more serious problem I'm afraid.

btw - all seperators supplied by porsche are the updated type.

I missed that part about the oil pressure warning light and the noises.

You are so right.

The oil light should not flash, unless the engine is running so poorly that its idle speed drops enough oil pressure falls away. Happens but it is rare.

For the noises... a leaking AOS can make the engine make funny sounds. Not necessarily whooshing noises though. In some cases the failing AOS can cause the engine's crankcase to experience considerable low pressure to the point a seal can leak air (the RMS for instance) or the oil filler tube can crack and leak or even the oil filler tube cap can leak (these can leak even when the AOS is working just fine).

For the seal the noise can be a faint howl or even a squeal. If the cap is leaking severely the air being drawn in past the cap can make a noise as it comes in past the seal/rubber gasket that seals the rear trunk fluid bay to the underside of the rear trunk lid.

Along with the above, if one tries to remove the oil filler tube cap with the engine idling in some cases the cap is near to impossible to remove against the pressure difference. I've experienced this firsthand.

A squeak though... that' s not a noise I'd associate with a failing AOS.

To the OP, best then to get the car flat bedded to a qualified shop for diagnosis and repair. Avoid starting the engine.

Sincerely,

Rockster.

[justinbaker]

Yes the oil light flickers at about 700 RPM idles ok at this. I thought that the air oil seperator was the cause of the squeeking sound.

What are the symptoms of a failed unit without it smoking?

[911Fiddler]

Tested my aos this year according to a procedure I saw written up. Fitted a plastic manometer tube onto the dipstick tube and measured the suction in terms of water pressure. It took 15 mins and mine was within spec at 5 inches of water pressure at idle.

[Rockster]

justinbaker said:

Yes the oil light flickers at about 700 RPM idles ok at this. I thought that the air oil seperator was the cause of the squeeking sound.

What are the symptoms of a failed unit without it smoking?

Well, first thing is you need to be sure that oil light flickering isn't something to worry about. And to me it is. Is the oil level ok? Do you have the right oil in the engine?

I'd not start/run the engine until the cause of that flickering oil light is found and fixed.

The symptoms of a failing AOS can vary based on my experience with 2 of them going bad.

The 1st one started out with the engine just a bit flat off idle, a bit hesitant. I tried various things to no avail.

About the last thing I remember trying, and I don't know why, was trying to remove the oil filler tube cap while the engine was running at idle.

While I could unscrew the cap I was not able to remove it with the engine running.

I think at this point I gave up my diagnosis and called to make arrangements to bring the car in to a dealer's service department. I talked to the service manager and after he heard a run down of the symptoms told me 'AOS' and do not start the engine.

I called a flat bed tow truck but the driver required that I position the car so I started the engine. At some point the smoking started in earnest.

But the engine was unharmed and the car soon back on the road.

The 2nd AOS failure the engine was running as best I can remember just fine. On a long road multi-day road trip. At the end of the 1st day when pulling off the freeway the engine emitted a bit of a stumble, a brief and not very severe stumble, but still notable because this was so uncharacteristic of the engine. Concurrent with this stumble the check engine light came on. I travel with an OBDII code reader/data viewer so I pulled the codes and they indicated the DME was at its enrichment threshold. I suspected the MAF and cleared the codes.

The next day and back on the road all day long and the engine was fine until the end of the day and again the behavior as the day before. Same codes.

Next day all day more driving and even though I stopped for gas and other reasons never a hint of any problems. I reached my final destination (after driving over 2K miles) and was thinking of where I could buy a MAF for my car. The first start of the engine the next morning though had oil smoke just billowing from the exhaust. The MAF was not the problem, obviously. And no need to do any diagnostics, and risk running the engine any. I knew then the cause of the stumble, check engine, error codes, was not the MAF but the AOS. Again. I then made arrangements to get the car flat bedded to the nearest dealer (over 90 miles away), and it just so happened to be the same dealer that had installed this AOS only years and maybe 100K miles ago.

Get that oil light flicker taken care of.
Sincerely,

Rockster.

[justinbaker]

Thanks for the help,

I wasnt concerned about the flickering oil light, and knew I had plenty of fresh in there. Its certain that the oil seperator has gone, as plumes of smoke appeared this evening on start-up. I imagine that my tickover was low enough to twinkle the oil light.