Originally Posted by scheidt27
I usually plug mine in below 20*. U can leave it plugged in as long as you want, it justs costs more is all. 4hr minumum of being plugged in for the block heater to do you any good as well.
There is no minimum time for leaving it plugged in. mines on a timer for 2 hours and heats my water to around 110 when its about 30 outside. If its colder than that, i still see water temps of 90 upon startup after 2 hours heating. If you only leave it on 1 hours you will still see it starts easier but 2 hours is better. You can leae it plugged in over night but your electric bill will reflect this.
Theres no magic number to start plugging it in at, its kinda pointless at 40* and 30* you will see your heater warms faster but the truck probably doesn't have a hard time starting at 30 so as stated, 20 degrees you will see the benifits of the heater when you start it.