I've done the search deal, and of course read a lot in books, but I can never seem to get the smoke deal straight, especially when it comes to plain ol' gray/white smoke. In understand why it's there on a cold start-up in a diesel, but what I'm wondering is why so many cars (both gas and diesel) emit whitish smoke during cold weather while their simply driving around. I realize this could be the world's dumbest question, but anyone who's familiar with me knows I'm not afraid to ask those. I see tons of vehicles with a little waft of white behind them in the fall/winter months, and I suspect my car has something similar ... I can never see it behind me, but sometimes when idling in traffic at night I can see it in the headlights behind me. Yet during the day I can stand behind my tailpipe and NOTHING is coming out (well, nothing visable). Why can I sometimes see this on winter nights? Is it a product of emissions interacting with cold air? What's the difference between "normal" smoke, smoke from unburnt fuel and smoke from a crack head? I can't imagine every car I see with a little waft of smoke behind it has something catestrophically wrong with it, so I suspect there's something obvious I'm missing. Anyone want to give me White Smoke 101?

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)