are you using 15/40 engine oil vs a straight weight oil .15/40 will give you faster lubrication at colder temps.Where I used to work the fleet was powered with propane and they circulated warm water thru the regulator to keep the propane from icing up.,in the winter we blocked off part of the radiator to make the heaters work,but these trucks were old with I think 160 f thermostats.but you still had to keep a good eye on the temp gauge as it warmed up thru the day.