Oddly enough just yesterday I saw an F550 dumptruck puff out a cloud of white smoke on accell, then stop. I was behind him and drove through the cloud, it didn't really smell like fuel or coolant, I just expected it was in regen. It was a City Works truck, so I am sure it never gets out of town. I have driven them and seen them puff smoke in a similar fashion, usually in winter after driving through town for a while, then pulling away from a stop. If they are running ok, not consuming fluids, and no warning lights on, I advise people that it is normal, and advise them to get out on the highway once in a while to complete a good regen.