Blowing white smoke out your exhaust? 996/Boxster

Most people’s initial reaction when they see white smoke coming out of their exhaust, is to assume the worse…..blown headgasket, slipped cylinder lining, catastrophic engine failure.   While on rare occasion that is the case, many times it is nothing more than a bad Oil Air Separator (OAS, AOS, Air Oil Separator, etc).

996, 997’s, and Boxsters use an oil air separator which basically reduces oil vapor that recirculates in the engine.  Unfortunately, they use a rubber diaphragm that is prone to failure.  The result is excessive smoke out of the exhaust on start up and driving.  Some smoke on start up is normal on a horizontal engine, but it shouldn’t last more than 10-15 seconds.  When the OAS fails, the car will start smoking for longer periods of time, until is a huge smoke cloud as you drive.  One of the other symptoms of a failed OAS, is a chirping or harmonic noise near the rear of the engine by the transaxle.  The noise is due to the air passing through a small tear in the diaphragm.  Once the OAS completely fails, the noise will probably not be audible as the air is passing through a large tear, and not a small one.

Fortunately the part is cheap at less than $150, and a couple hours to replace.

I cut open a recently failed OAS that was starting to not only make noise, but also cause some light smoke issues.

You can see the main tear in the middle (red arrow).  There was also another tear about the same size near the perimeter on the other side which is hard  to see.

911Air Oil SeparatorBoxsterMaintenance

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Randy - Seattle, WA

October 2, 2009 at 9:43 PM

This just happened to me at a PCA track-day on 10/1…Everything was going well and I had done one of my four sessions for the day. My second session was up and when I started my 2000 996 C4 she started smoking like a freight train…Immediate thoughts from fellow track day folks was a blown head gasket, 3.4L is bad, I need a new engine, etc…I drove it home and the smoke cleared up but I’m sure my OAS is bad so I’m replacing it this Monday…thank god because I’m not ready to do a 3.6L swap. My 3.4L has 99K and runs very well…I’ll be installing new plugs along with the OAS.

geeroms pascal

September 29, 2012 at 12:08 PM

Hi,the part you show on the photo failed on my 996 and some off the oil got into the exhaust and air intakes.
So my question to you is;i already sterted to get the engine out for better acces and once the intakes are cleaned and the part is installed,how do i get the oil out off the exhaust?Do i start the engine and let it burn out???


    September 29, 2012 at 6:43 PM

    Sure, it will burn out of the exhaust pretty quickly. Shouldn’t be enough to hurt the cats.

Eric Bartlett

January 2, 2013 at 8:18 AM

This just happened to my 2008 Cayman, this seems to be a manufacturing problem, faulty design or part, why doesnt Porsche fix this? or initiate a recall? My Cayman had less than 25000 babied miles on it. the Porsche dealer wants to charge me $1100.00 to do the repair, does that sound right?


    January 2, 2013 at 12:20 PM

    Hi Eric,

    That separator is a little more expensive, but not that much. I would find a qualified independent shop who can save you a lot of money. Oil separators are used on many different cars, Porsche is just one of them. They all have issues. Unfortunately, I can’t answer for Porsche 😉

Bart Flannery

August 20, 2013 at 5:30 PM

Same issue with 2007 boxster. Only 20k but started puffing at about 15 k or so. You would think Porsche would come up with a fix and recall since it seems to be chronic problem? It’s not like these are Camry’s with a couple of million cars out there. Doesn’t matter still absolute hoot to toss around back roads of Penna. I’ll get it fixed when it gets embarrassing.

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