Never have ran one or needed one
You will know if you need one if you’re freezing in the cab
Also. I’ve seen some guys with the entire grill buttoned up. I’m not 100% certain but I think you need some flow otherwise you restrict your engine sorta like putting your hand over the end of a vacuum hose
The motor needs to draw air from somewhere
I know people would do that to their cars in the winter and have always heard to leave some opening
