Yikes smoke!

I recently ran my first autocross a couple of weeks ago. Great experience and can't wait to get out and do it again, but that's another story... Towards the end of the second day (it was a 2 day autocross course through PCA), when I started my car - 2003 C2 with ~ 41,000 miles - I noticed a significant amount of white smoke coming from the back of the car. It only occurred on start-up on the last run of the day and has not happened since. I've run in several DE events before this happened and never had this issue occur before. I'm wondering if this is an indication that the AOS is on its last legs or some other issue brought on during the time on the course. The oil level is at the upper end of the range, but it isn't overfilled - at least doesn't appear to be based on the dipstick. I've done a search on the site and seen some mention of the fact that the AOS can fail as a result of extensive tracking/autocross, but no mention of a situation that is close to mine where the smoking completely stops. All other threads I've read indicate that a failed AOS causes a lot of smoke to come from the exhaust, which doesn't seem to be occurring here. I'll be taking the car in for an oil change soon and am wondering if I need to raise the issue of the AOS as well. Interested in any thoughts from people far more mechanically inclined and knowledgeable in this area than I. Thanks in advance.

IF it was a one-time only thing and has not happened since AXing your car, you may have just had too much oil in the car and overwhelmed the AOS and/or had an instance of "puff of smoke when restarting after driving the car really hard" syndrome. Some folks will tell you to drain half a pint of oil, but OTHER folks will tell you to never track your 996 without the oil at the full line. Opinions == a**holes, unfortunately, so you get to decide how you feel about the oil level. Since the issue has not persisted, it seems less likely that the AOS gave up. Read some threads here about AOS and suction on the oil filler to get an idea of what's normal and what's not. A single puff of smoke in my opinion after a hard run is not a throw-parts-at-it dilemma - my 986 did this a time or two after especially vigorous AX with no ill effects. Others will encourage you to freak out. Freaking out is expensive. Waiting too long can be expensive, too. I'd rather be a little more methodical and see if a problem actually exists before fixing it - a new AOS is no guarantee that you won't blow your AOS the next time you're out AXing anyway, so it's not really as great a PM candidate as, say, the water pump. All IMO. Which is often wrong + laced with irony, sarcasm, sarcastic irony, and/or ironic sarcasm.

Some folks also let the car idle for a minute or so, to let the AOS catch up with dispersed oil & excess vapor, after a hard run. This is to reduce "Puff the Magic Smoke Screen" on restart.

Thanks for the input guys. I read plenty of information saying something along the lines of AX'ing will cause your AOS to fail. A little surprising to me given the cars are designed to be driven hard. I never realized that the 996 was so dainty. Some suggested upgrading to a motorsports AOS, but at over $700 for the part, that seemed excessive to me given the amount of track time I get in any given year. Letting the car idle for a time after coming off the course makes complete sense and seems like common sense...of which I apparently have little. Thanks again guys!

Mine did the same after a track session - was not running oil at full - maybe 1/2 way in dip stick - no issues since then and that was with a new aos over a year ago ..someone told me back then to let it idle a few mins - yes I was also surprised you would need to do this on a 911 - even after a cool down lap Keeping revs below 5k ..... Dry sump engines are better suited for high G work I guess ...

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While the car is sort of intended to be driven hard, the AOS ain't. Auto-Xing can send an AOS over the edge in no time. Even if the AOS is "OK", hard driving can generate way more oil vapor than the AOS can remove from the crankcases fumes. These fumes are routed to the intake where they have to make a very sharp turn. The fumes make the turn, the oil vapor impacts the intake wall and wets it with oil. If you park the car then and shut off the engine this oil warmed by the hot engine -- the intake is generally cool while the engine is running but heats up from heat soak when you turn off the engine -- the oil runs down and collects in one or more cylinders or on top of the valves. When you start the engine this oil is pulled into the combustion chambers and burned incompletely and smoke is what you get. Be sure when you Auto-X the oil is fresh. Do not overfill the engine but do make sure the oil is if not at the max line very close to it. (Frankly I would not try to get fancy I'd just make sure the oil level was at the max line.) Before you come off the track take a cool down lap and during this lap switch on the A/C. This turns on the fans -- they may already be on -- but if not this gets them on and this helps cool the engine down. Back in the pits let the engine idle a minute or so then shut the engine off.

At my last Auto-X I had the same thing happen... looked like a James Bond escape smoke screen. I have an Auto-X this weekend, and will try to remember that tip about running the AC after a driving session. (They don't allow "cool down laps" but I can find a place in the back forty to drive around).

Also have this from time to time. In the western part of Norway we have mostly narrow roads with lots and lots and lots of twisty turns around the fjords and tunnels of course. So it's quite fun to drive a 911 here. But sometimes upon starting there is smoke, white smoke, and I have also experienced bluish colour, might be my imagination about the time it was bluish though. I have heard different explanations to this. If it is frequent, it might be the AOS failing. If you do a short drive in your car, like a 2 minute drive, shut it off and upon restarting there might come some smoke. This due to the different metals the engine consists of warming up unevenly, creating gaps for the oil to seep into the cylinders after shutting off the engine. And the third being vigorous on the fun pedal around twisty turns without the cool down before stopping. Also when me and a friend went to buy a 996 that had stood still for three months, it did smoke quite a bit the first minute after starting the engine. He does not have a problem with this after purchase.

Mine did this when I started it in my garage in the morning. The AOS is about 3 years old so it should be okay. But my wife thought maybe there was something on fire and called me concerned after I left. It's also done it at the track even when I leave the car running at idle for a while. Never thought about the A/C trick but it did do it less when I didn't have the oil filled up the whole way. Unfortunately right now I do as I just changed the oil recently.

This is very good information for my upcoming track day.

RE: AC during a cool-down lap...If the safety crew sees anything dripping from your car, you've got a good shot at getting flagged off.

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Won't be any water dripping that soon after turning on the A/C. Might see a bit of water trail when turning sharply into the pit parking space. On the way out of the pits back to the track the A/C should be off and by that time any condensation dry. Still, if it is a concern and if even water from condensation has one at risk of being black flagged leave the A/C off. Just take the cool down lap if possible. If not back at the pits let the engine idle for at least 2 minutes before shutting it down. This is what the Turbo owners manual calls for -- and this would probably be the bare minimum for a N/A car "hot" off the track.