My 2004 superduty 6.0 just started puffing out white smoke. It seems to do better once it has warmed up(gauge half way between cold and hot) is this a bad fuel injector or just a clogged one. Put an additive in today when I filled up so I will see what it does.
Could be either fuel or coolant related. Depending on the smell as was stated above. So first thing, have somebody rev it WOT for a second and stand back there and smell. If it smells sweet or fishy, that is coolant. If it smells like a mixture of fuel and exhaust, it's obvious the issue. Have a look at your degas bottle and look for obvious loss of coolant (it should be at the min line), or discolored coolant. Next, check your oil and see if there are any bubbles or milky substance on the dipstick. Hopefully it goes ok, good luck.