driving around town yesterday, I saw a 1999(?) F-250 X-cab 4x4 with a 7.3 blowing a ton of white smoke out of the tail pipe-smokescreen style. I am glad that it was not my truck, but what would cause this? The guy driving didn't seem too worried-it would be hard to miss. Just wondering

 

Family had a Chevy 6.0L long time ago. Started pooring out white smoke one day while running errands, so we drove it home fine. After that it wouldn't start again. Found out it was a cracked block. Coolant mixed with oil causes it.

 

Since the truck you saw was a diesel, my guess would be that it had a blown injector O-ring, and what you saw wasn't actually smoke, though it looked like it. It was likely unburned fuel passing through the system, and coming out as fuel vapor. When my truck blew an O-ring, it was unbelievable how much "smoke" comes out the tailpipe.

 

Or some dope put unleaded in it. Guy I worked with did it once and it smoked like a factory steam pipe.