diesel fuel itself needs to be heated at -20 C and below. I used to have a diesel car which would start itself up periodically when its fuel temp was getting close to -20 C, just to warm up the tank & pipes.

Yeah, the 1999 diesel truck I had did the entirely opposite thing: it had a 120v electric block heater, so you'd plug it in when it was cold. (In New England, I used it once to see how it worked, but never actually needed it in practice.) At the time I saw stories (I never confirmed in any depth though) that Minnesota had 120v outlets on parking meters, giving some sort of weather-encouraged compliance :-)