This is my first diesel, so this may be a stupid question...I don't know. How long do you need to leave your truck plugged in for the block heater to be effective? I am wondering if it needs to be plugged in over night or just plugging it in for an hour before you want to drive it will work. I am just looking to use as little electricity as possible. Also when do you guys start plugging them in? When the temp get below freezing at night? Or are you just starting them on the glow plugs and using a non gelling fuel treatment? Thanks for any help.