my dad plugs all his trucks in at night once it hits 28 degrees out regardless if he is going to use the truck during the day or not. ill say his.. this dodge sprinter van starts up like a champ during winter.As does his duramax. Block warmers are a life saver. we have a diesel tractor that doesnt have a wamer built in for some odd reason and she takes a while to get warmed up on those cold days specially when we use it to blow the driveway out at my parents farm.