[terryf]

Having slept in quite cold temperatures in cars during longer trips quite a lot of times, just having the car idle over-night has always been enough to keep the cabin warm enough to not even need a blanket. Not talking about luxury cars with huge engines either. It also uses very little fuel. After 8 hours, you can see that the fuel gauge has moved, but only very slightly. I'm pretty sure a ICE car with a full tank can idle for several days before running out of fuel.