1992 Dodge Colt white smoke from exhaust.

My smoke problem presented itself a couple weeks ago, but then stopped for a couple weeks and now has come back. The smoke is not constant, the exhaust mainly smokes when the car has been idling for a few moments (like at stop signs, and traffic lights) and it bellows out a big cloud (not dense) of white smoke. It does smoke a little when I go really throttle heavy, but It kind of seems like the car is smoking mainly when it is atmospherically cooler out (it's cooler now, and the few weeks ago when this problem first presented itself, I think it may have been cooler, sub-50 degrees F). The smoke smells more carbon like (burned fuel smell), at first it kind of smelled like a burning clutch you slip the clutch a lot, but it has gone to more of an actual burned fuel smell. When letting the idle while parked, you can't see any smoke coming out of the exhaust, then if I rev the engine, a cloud of the white smoke will come out, and it will stay smoking a little for a minute or so, then will quit smoking. Only things previous that could possibly be relate are:1. Cast iron exhaust manifold is cracked, 2. Atleast weeks is not a month before the first incident my radiator has a crack on the top plastic piece, steamed out a lot of the coolant. That was just before I had to go into class, so I shut off the engine, and proceeded to class. After class I had to drive to walmart with the cap off the radiator (hoped that less pressure on the coolant will prevent warm coolant steaming out that crack). The car got hotter than it ever had before, but did not get to the red overheating zone on the temp guage.