Thanks to all who replied. It sounds like no one has actually done it, and most seem to think it's not necessary. I read about the thermos that keeps the hot coolant, but I wonder after 8 hours of being at work on a 0 degree day if it will still be warm. Also, the passenger compartment, steering wheel, seats, etc. will still be pretty cold for a while. As someone else pointed out, it would be nice on a hot day in summer to have the car cool when you get into it. I know it goes against the grain of gas economy, but this may be one sacrifice I'm willing to make. Maybe if the car had heated seats ...firepa63 said:Jim, I don't really think you need one. The car warms quickly and there is supplemental electric heat that initially comes on as the coolant warms up. In addition, there is a thermos that stores hot coolant at shutdown. This is pumped back into the system at startup.