My dad used to build a fire under the old Cat bulldozers years ago.......lol
I have a heat lamp I may strap under there for an hour or so if its too cold.
One of my antique tools is a Sears engine heater. It is the same as the old roadside warning lights that burned kerosene but has a perforated can over the flame. I've never used it(it is still in its original box from 60+ years ago. But, I'm prepared if I need it.
One of the winters in the 1930s my grand father had to build a small fire under his car to get it started. That was the winter that the western end of Long Island Sound froze over and people walked from Connecticut to Long Island. I can see doing that under a diesel engine but not a gas engine. My grandfather was a bit of a daredevil especially on his old Husqvarna motorcycle. Good Luck, Rick