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Joined: 19 Jun 2017
Posts: 31

PostPosted: Thu Jul 25, 2019 7:18 am    Post subject: Preventative Maintenance 997.2 - Air Oil Seperator Reply with quote


I have a 09 997.2 and noticed that if I park the car on a banked road ie the passenger or driver side is higher or lower then the other side when I start the car up there is a bit of smoke. No smoke if the car is parked on flat ground or if its parked with the engine lower than the front. I looked into this and apparently it could be caused by the AOS diaphragm failing. In my case I think its more linked to the design of the engine and isn't a big deal.

Do you think its worth replacing the AOS as a preventative action, its about £80 from design911 and I plan on taking the air box out and replacing the drive belt in the weekend anyway...
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Joined: 10 Jul 2016
Posts: 150
Location: Adelaide, South Australia

PostPosted: Thu Jul 25, 2019 9:18 am    Post subject: Reply with quote

This is a common issue due to oil seeping past the rings in a flat six engine.

While you can change the AOS if you want, it won't change the situation with the occasional smoke storm!
Long time Porsche fan. Previous cars include 911T 2.2, 911E 2.2, Carrera 3.0, 986 Boxster S. Current car is 997.2S Manual (with PSE, H&S Backbox bypass, Sports Chrono, SSK, DSC PASM controller, Carrera Sports wheels, Ducktail/Diffuser and splitter, Sport Design steering wheel etc.)
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Joined: 21 Mar 2015
Posts: 7808
Location: Brighton

PostPosted: Thu Jul 25, 2019 6:14 pm    Post subject: Reply with quote


i doubt an AOS change will make any difference .. these tend to fail slightly differently to the early cars in that they kinda block .. a high pitched squeal is more of what happens .

They can cause smoke but i've yet to see one where the road behind you becomes obscured in smoke .

AOS and it will always be both exhausts that smoke as the oil is getting into the inlet manifold and being burnt both sides ... obviously it only gets there when the engine is running as an AOS does nothing when its not running .

Edit ..

btw .. when changing the drive belt then please check the tensioner as per this post .

My Daughter's Crowdfunding has hit the target .

Thank you all so Very much .

She's not going until july 2020 though .


7pm - 9pm

Indy Mechanic .
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Joined: 12 Feb 2014
Posts: 104

PostPosted: Thu Jul 25, 2019 7:30 pm    Post subject: Reply with quote

The AOS went on my wife boxster recently, 986, it was at high revs under acceleration joining a duel carriageway, the smokescreen behind would have made James Bond proud and both carriageways were covered and all traffic slowed to a crawl until it cleared.

We pilled over and I checked the crank wasnt on the road and set off after 5 minutes without any issues bar a puff if rapid throttle applied.

D&G replaced the AOS and the car has been fine ever since.

Cheers, Paul
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