Im from Canada where it somtimes drops to -40 c {-40 f},Most people run synthetic oil in there deisels here in winter.But that stuffs like 25 bucks a gallon here so i put in a bolt in oil pan heater{10 min to instal} and now i have no problem starting with 15/40. Also with good batteries my truck will start not plugged in running 15/40 down to -25 c{-13f} but will hammer alot.