Just to add to the possibilities, perhaps it is your engine upper end cleaner working. I have 2x before used Red Line Complete Fuel System Cleaner (http://www.redlineoil.com/redlineoil/si1ti.htm
) and each time my car has ejected plumes of white smoke. The key difference is that in my cars experience the smoke comes out in a very short time frame and in MASSIVE amounts.
PS: The coolant loss is probably unrelated. Check the heater hoses.... A lot of folks miss this because it's hidden. In age and use, the hoses may be due for a change or just a clamp tightening