[thstone]

Could be normal or could be AOS.

It is somewhat common to get a big billow of smoke on startup that will fill your rearview mirror. In fact, the first time it happens you will think that your engine just blew up! As long as it only happens occasionally, there isn't anything to worry about.

It could also be the start of a failing AOS. If so, don't worry, it will get worse and you'll be laying down smoke screens worthy of James Bond very soon. That will be the clue that tells you to have the AOS replaced.