Today noticed white smoke in the exhaust of my 99 Deville which was very heavy for a few minutes. At idle it cleared in less than 5 minutes. Temp was about 40 today but colder last night. Car has 120K miles on it. Otrherwise runs and accelerates fine.
Coolant temp about 197 to 208 and drops when accelerating. Is this the head gasket problem? Uses a quart of oil about every 800 miles but no leakage of any kind dripping from the car.

 

Steam, unlike smoke fades away quickly. Smoke, unlike steam hangs over the car and usually has an odor. So, my thought is you are seeing steam which at 40 degrees, would be NORMAL!

 

Wouldn't hurt to start thinking about the thermagasket solution.

 

a number of things to look into: a leaky valve seals, engine coolant/Antifreeze being processed in the combustion chamber(s) of the engine, head gasket failure, intake manifold gasket failure or probably steam water vapor due to either an engine coolant leak evaporating rapidly into steam as it escapes from your cooling system. I guess, it would help to check on all your car parts and see what might be the real cause. I've experienced it before and it was because of a leak on my head gasket.