soren.911

DBJoe996

Left side exhaust is Bank 2, right side of engine where the AOS breather hose vents, so it does sound like an AOS problem. It is not that unusual for an AOS to go bad, even a new one out of the box. True test would be the manometer on a modified oil filler cap to measure the crankcase vacuum. There are some threads on here on how to do that and some benchmark measurements. I sure would do that before tackling an AOS replacement project, unless you are not the one doing the work. How old is the AOS now?

Cosmo Kramer

Do you drive the car hard right before shut down or are you just putting around?

jumper5836

A bad AOS will smoke all the time. Also isn't there a check where you can have the car running and then remove the oil cap, the car will run rough if there is a problem but a good AOS will compensate quickly and will run smooth. Having a puff of blue smoke at cold startup is normal for a flat-6 as oil can get past and pool which is burnt off at startup.White smoke is just the water condensation in the oil burning off.

Mike Murphy

adh

If you are adding gas additives they will cause smoke on a cold start up.

jandackson

NYoutftr

+1
This happened with my car

soren.911

Ahsai

How did you clean the intake manifold? They can hold a lot of residual oil where the three runners merge so you need to go very deep on both sides.

Also use a manometer to measure crankcase vacuum (from the oil filler tube) and it should be around 5 inches of water.

soren.911

Nickshu

Mine does a large puff of smoke after sitting for awhile or after hard driving. AOS tests around 5 with my manometer. I do have some oil in the intake last time I had it off. I have not investigated further but curious what turns turns up from this. Could an AOS be bad yet still show a normal reading on the manometer?

DBJoe996

Damn things are a bit complicated. They are designed to capture oil in the crankcase fumes, drain the captured oil back to the crankcase and vent the crankcase fumes (ideally without much vaporized oil in it) to Bank 2 and to the Throttle Body (vent lines 4 and 5 here http://www.autoatlanta.com/porsche-parts/hardparts.php?dir=996-99-05&section=104-10). The puffs of smoke, oil in the TB and intake plenum, James Bond smoke screens and smoking after hard driving or sweeping right handers are all a result of the AOS being either marginally bad or being totally overwhelmed by oil sloshing around in the crankcase and getting sucked up into the vent lines. The crankcase should be under vacuum, but under certain say hard aggressive driving at high RPM's, there may be much less vacuum which affects the overall performance of the AOS. Normal reading on a manometer at idle may not be indicative of what happens to the AOS under full running conditions. At best it is a crappy plastic device that is a PITA to replace and is the source of great consternation to many. I believe even Jake mentioned one time that he has found new AOS's bad right out of the box. Given the fact it is heated by coolant lines and there is just a cruddy diaphragm separating the coolant/crankcase fumes, there is one more major PITA thing to go wrong.

Pretty good read on AOS testing and function https://rennlist.com/forums/996-foru...this-mean.html

I would not worry so much about a puff of smoke. It is actually quite normal to have some oil in the intake because of the mist of oil vapor being vented by the AOS. I have a good, functioning AOS, and every time I remove the TB for cleaning I always find a light coating of oil in the intake plenum. It is not normal to have the intake overwhelmed with oil and creating a smoke screen. But, overall, it is still kind of a crap shoot with the AOS.

Nickshu

I believe I have read posts that the Motorsport AOS will improve this issue but they do not show any greater reliability than the stock AOS. If I recall from prior conversations here on RL some people "in the know" have found the motorsport AOS's fail just as much as the stock AOS...at several times the price. That said I may need to spring for one the next time around.

My understanding is the mode of failure of the stock AOS is that the rubber diaphragm gets a hole in it and allows oil thru (along with crankcase vacuum) - Hence the irregular manometer readings when it's failed. Is there a way for oil to bypass the AOS then even if the diaphragm is intact? That would appear to be what is happening on my 996 as it tests around 5 on the manometer.

I am running my 996 mostly on the track with track suspension setup and Hoosier R7's. I do have a 2 quart deep sump and run the oil level at the bottom 3 bars as recommended, but still appear to be picking oil up into the intake somehow....evidenced by a big, brief cloud of smoke at startup. Interestingly if I come off track and the car sits for say 1 hour, when I restart I don't get any smoke. If I let it sit for 2-3 hours, or overnight I get a big smoke at startup the next AM.

DBJoe996

I don't know if the Motorsports AOS will work on a Mk1. Most say it only is for the MkII engine. Anyway, interesting reading http://986forum.com/forums/boxster-g...s-failing.html