MG> - 30 is a little harsh on an engine. You should plug it in sooner if you
 MG> want your car to last longer.

That's true.
I use mine even at -5 C.

 MG> Most people don't realize that you don't need it plugged in all night
 MG> though. You only need about a hour and a half for it to warm up, but no
 MG> one wants to get up early and go out in the cold to plug in their car.

3 hours is max. After that it doesn't do any good. The engine will not be any
warmer.
I have it connected to a whatch that runs it for max 3 hours

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