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Replaced air oil seperator, now I've got an oil leak

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I first posted this in reply to Beelzy's (8-8-08) "Smoking after short trips" post. Since we are so frequently having air oil separator (AOS) problems (and I got no response), I'm giving it its own topic.


I had the billowing smoke adventure about a year ago with my '00 base Boxster with 40k miles. It was the AOS, which was replaced by a local shop along with the rubber portions of the oil filler tube. Question -- my car never leaked any oil until this work was done, now it has a very slow but persistent leak. How much? After my 10 mile urban commute the spot may be about 1.5 inches in diameter, after a long hard drive the spot may be 4-6" in diameter.

The shop claims the problem has nothing to do with its AOS/filler tube install, and I have not been able to see any obvious source for the leak when I get under the car. They explain that the crankcase pressure is higher now that the AOS has been replaced, and that the the leak is caused by an old seal and this higher pressure. Hmmm.

I watch my oil carefully (and no longer park in my brick driveway) but have not resolved the annoying problem. I've been planning to take it to the dealer (HBL in Northern Virginia, near Washington DC), as I've a bad vibe w/ the mechanic.

Any thoughts?

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Hi jefla,

I am not an experienced mechanic, but the adice I could give you is what I would do in your situation - locate a reputable Porsche Indy in DC (lookup or ask around the area's PCA), if not possible, take it to the dealer ASAP. These engines are precision instruments and a oil leak is never a good thing, or something you can get away with...

Best of luck,

Keep us posted.

Edited by gandrade1
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A leaking AOS causes higher crankcase pressure. I know of at least one dealer shop that put a pressure gauge in an old oil filler cap. When they suspect an AOS leak they put the gauge cap in place of the normal oil filler cap and look at the pressure reading. An AOS leak will give a much higher (crankcase) pressure reading.

They need to find the source of the leak.

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I "vibe" is always a good enough reason for me to find a new Indie, so I cannot question that. My two Indies are like extended family to me...it's the only way I can almost trust them. :P

With that being said things constantly happen to cars that do not have to be cause and effect. I ONLY buy 5+ year old cars and have owned atleast 25 such animals in the last 15-20 years. I can tell you many times when we fix one leak and three days latter the other side starts to leak. It's very common for non-DIY'r to get all cranked up when such issues occur assuming the worst that the Indie is to blame.

If you don't trust them prior to this fix, then walk away. If they guy said it COULDN'T be the issue w/o looking at his own work, then walk away. If he's willing to take a look or consider his work could be at fault then he's worth keeping.

Is the leak 100% below where the AOS is located?

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