You don't want to spend more for electricity than you save driving a diesel LOL

I have mine on a timer, turns on the heater 2hours before I leave in the morning, heater is toasty-warm as I back out of the garage and little smoke. Starting problems weren't the issue, just better for the engine and my cold fingers in the morning.

You can leave it plugged in all of the time, I used to with my CAT diesels, just takes electricity but it's ready any time and warm.

If it's about preventing starting problems I'd imagine that depends on the condition of your engine, the oil used, your starter and battery, vs the air temp. I'd think that any M-B diesel that wouldn't start at 20F or above without pre-heating the engine has other issues to be dealt with.

- Jeff Miller
190DT in Michigan