Our cars sometimes emit a puff of noxious smoke on startup. Sometimes it's a large cloud. Sometimes it envelops the neighbor and their entire family as they're heading out for a walk .

Perfectly normal, I know.

It's still annoying and sometimes embarrassing. Anyone know of a fix *besides* driving the car every day?

 

The "fix" is to replace the factory AOS with the UAOS design....

My 996 has 189k miles and has never let out smoke on start-up ,,"except" for when I almost lost my engine on the Track a few years ago that led me to Invent the UAOS...

I was at a Track Day at Little Talladega and after the 1 hour lunch break I went to start back up to go back out on Track and a huge cloud of smoke emerged.............It was very embarrassing and scary as I knew3 what had failed and that I almost lost my engine due to the feeble AOS design.........I had to dissabled the AOS to keep from engine damage potential and "limp" home ending and ruining the rest of my day...

Some will say that smoke on start-up is due to the flat engine design, this is not entirely true...

If your car ONLY smokes after being parked leaning to the side , then the flat design can be blamed..

If your car smokes when parked on a level surface, then you have poor ring seal or you have oil dripping down from the intake due to poor AOS function...

There are just too many cars that do not smoke EVER to say it is normal...

 

John, definately not perfectly normal. The smoking you describe means you have a bad AOS. The OEM AOS is a frail and poorly designed piece. Instead, get yourself the UAOS. If your smart, even if you don't plan on tracking your car, get the UAOS track version. You won't ever have to worry about it failing again. Not to mention it can handle an extra quart of oil above full if you accidentally over fill it. Some guys panic when they think they over filled their oil. With the track version you won't have to worry about it. Your family, friends and neighbors will thank you. 👍

 

You can also get “smoke” from starting the car, running it for many seconds and then shutting it off. It’s when it’s being started without being warmed up. It’s excess fuel and water vapor that collects in the exhaust.

 

Mike if you are getting smoke after a few engine cold starts you may want to check your fuel trims....Make sure they are very close to "0"...

I have seen this happen on cars that are running a little on the rich side. The cold start mode is "open loop" and disregards the 02 sensors untill they get heated up...and can even still be in the window of adjustment to keep from setting a CEL..

 

Huge continuous plumes of white smoke at startup is a pretty good indicator.

You can also use a manometer to check the vacuum, or you can see if it's tough to remove the oil cap due to high vacuum when the car is running. If it is, you have another indicator that it's AOS failure.

It's not a matter of if the Oem AOS will fail, it'sa matter of when.

I had 2 oem aos failures in the mid 2000s. Had enough of the oem aos at that point and went to the motorsports aos which was the only solution at the time. Last year I did a 10 year engine refresh and went to the UAOS track version which is the best solution today for a long list of reasons.

 

There's so much misinformation out there, I've been accepting something I shouldn't - thanks for the clarification.

I just had my AOS replaced a couple of years ago, and I hardly drive the car, so I'm not sure that's the reason. Good to know folks recommend the UAOS - I might go with that next replacement.

I do work in the garage a lot, so there are plenty of cold starts - any info on how to check fuel trims?

​​​​​​One time in the middle of the pandemic my fuel went bad. My understanding is this can happen after a few months for fuel with ethanol. I've been only putting 1/4 tank in it since, and refueling every 3-4 weeks. Could it still be bad fuel?

 

I'll defer to Mike on that one.

 

I dont think bad fuel will cause the smoke unless it cause a very long crank and extra fuel in the cyl. Start with the easy stuff. Test the aos with a manometer. Then grab a scanner the can read the fuel trims. Then i would move to oil anaysis that checks fuel dilution. Ultimately u may have a leaking injector. This can be tested with a fuel gauge. Fyi, bad injectors r very bad for our engines.

Again start with the simple stuff and remember to diagnose before tossing money and parts at it.

 

My car will smoke if it is started, run for a minute when backing car out of garage and shutting it down to wash. Then starting it up to move back into garage.

the next day on the next cold start, it will smoke.

So now, any time the car is started, I will drive it to operating temps before wash and then again after wash.

I have never seen it smoke again.

 

My 996GT3 smokes at cold start up almost every time and it does not even have an AOS.

 

The plume of smoke on start-up from a failed AOS can be significant. Age means nothing towards the dependability of an AOS. There is a big difference between a significant cloud and a puff. Maybe the OP can film it. Everybody's definition differs.

Sure helps if you are running properly functioning fuel injectors as well. Not to mention coils, plugs and maf. But cels would most likely appear if their were problems...

 

Yeah, that’s what I’m sayin! I don’t think it’s just us two either. But like Skip said, I should check my fuel trims.