White smoke - you sure it's not just the condensation that occurs as it gets colder outside? Engine's burn gasoline in oxygen - the biggest byproducts of combustion are H2O (water) and CO2. When you start up a cold engine, that water in the exhaust stream condenses out in the cold exhaust pipes/mufflers - so you see water spitting out the back and a stream of vapor/fog out both pipes until the system warms up enough keep the water evaporated. If you have only short drives in the winter, you can have 'white smoke' all the time -- very hard on the exhaust system in terms of rusting from the inside out.
If you're loosing coolant out the exhaust pipes (as in failed head gasket) 2 things will happen - 1) you can smell the antifreeze in the exhaust very clearly. If you're not smelling antifreeze in the exhaust stream, then you can't be loosing too much there; 2) your coolant level will be lower. Are you having to constantly add coolant?
Assuming that's not the problem, you probably have a t'stat that has failed and it's stuck open. Upon failure sometimes they stick open and sometimes they stick closed. When they stick closed, you overheat quickly. When they stick open, the car won't warm up.
Hope that helps.
