It is all about the plan...so say you have a Cummins...it has 12 quarts of oil in there...When it gets down to freezing or below...it is thick, like syrup. But, you know your driving it the next day....just plug it in the night before, and when you fire it up, you get heat inside real quick....these big motors take awhile to heat up by the way...if you don't pre heat. If you have one and have never used it, try it, even if your not in freezing temps...anything below 45f. Most will not have this option but you can install one aftermarket if you need it. Most people don't even care about this stuff, but when you drive for a living ...it matters.
