Does it make sense ? Problem with local mechanic !

[Umbakrail]

I had problem last summer (2011) with air/ oil separator. I had an air leak (confirmed with a smoke test) on it with check engine. So local mechanic (who does only porsche and mercedes) replaced it.
Since then I noticed sometime on cold start I get smoke from the exhaust. Not the usual litte blue smoke puff. Il start 3-4 sec after engine startup and goes for about 10-15 sec.
Car went to sleep for winter and the problem is still there since spring.

I had 100 000km big and expensive maintenance this spring performed by the same mechanic. I talked about the problem and he said it's you air/oil sep. When I said we just changed it he said the I is probably something else.
He saw no sign of any problem with sparkplugs, I have no coolant leak and no oil consumption.

He suggested to replace the crankcase vent valve (said it's located on engine head ) wich I agreed to do and paid for . He said there was a lot of oil in this line from throttle body to valve vent so it should be my problem.
I see no difference since then. Some morning its perfectly fine while some I just disappear in a big cloud of smoke .

He agreed to change again air/oil sep on warranty if vent valve was not the solution at that time.
Now (I called im back) he wants me to run the car with oil fiiling cap very loose for 2-3 days tho diagnose the problem before he change air/oil sep. He say if smoke goes away its oil in the vent line and air/oil sep is the problem and he will pay for it. If not he say a cylinder probably have a big problem[
I dont feel safe tu run without this cap in place on the road for 2-3 days . I'm afraid my engine can suck up all sort of dirt and water.
It seem to me he only try something not to pay for a defective part.
Porsche dealer is at leat 2h from me so it's not easy to have another opinion.

What do you think/suggest ???

Car is a 2002 Boxster S
103 000km
Engine feel good and pull strong as usual.
no prestone loss or oil level problem.

[BerneseMtnDog]

Ask if the vent line was also replaced when the new AOS was put in. Often times it's overlooked and can also be bad.

Steve

[Wayne 962]

You should also clean out the intake when you replace the air-oil separator. But, that is probably not the problem here. It's unlikely to have "another" defective part. Or, you have a defective crankcase ventilation valve, which caused a very high vacuum to occur in the engine, which then damaged your new (and probably old) air-oil separator. Simply putting in another one without fixing the vacuum problem may only cause the next one to fail as well.

-Wayne