It seems to me that if you plug 'em in all the time then they get "used" to being plugged in. Then you get to a place where there is no plug and it will be a lot harder to start, I'm talking zero degrees or lower. Kind of like wearing a zero degree parka when it is 40, then wondering why the parka doesn't keep you warm at zero. It is what you are used to. I know engines are not "living" things and this does not make logical sense.

I'll see a few below zero daytime highs. This would be parking at work without an outlet, so I don't use the block heater at home in an unheated garage.

I've never used fuel treatment, if the area is cold the fuel is "winterized" in the winter. Though I would not buy fuel in LA then head into the mountains without treating it.

If I lived in "Frostbite Falls" I would reconsider the block heater. I've owned diesels since 1977 and this has worked for me.