I took my '67 Imperial out for a drive the other day, finally a warmish day! After about 10 minutes of driving a small amount of smoke was curling from the vent to the left of the temp controls. The temp control was off. What is the most likely root cause and is the fix a major project? Another clue, maybe, early in the winter I added additional coolant to the radiator and turned on the heater to circulate the coolant through the heater. I began losing coolant until I turned off the heater (coolant was running down behind the engine but not on the floor in the car). Is this related or another problem entirely?