As a rule Either is very destructive to an engine. In diesels I've seen it bend the connecting rods. For Air Cooled rigs, like Snow Trac, one can preheat air with one of the AUX heaters and run it into the pre-heat/Clean air tubes. This would be a good idea for ambient temperatures below minus 20 degrees F. For both water cooled and air cooled rigs there are a variety of plug in (120 Volt) heaters for the cooling system and the Oil system available. Also with both Gasoline and Diesel Vehicles as most Canadians and Alaskans will tell you," with Synthetic Oil it will start 20 degrees colder than with regular oil".