Decades ago, we had a club Cessna 140. In really cold weather, the starter was marginal, and it was impossible to successfully "prop" a cold engine.
The FBO wanted about $20 to preheat the aircraft, so we figured out another method.
One of the club members had a Corvair with a gas fired heater, much like the VW Beatles option in later years.
A piece of wood in a side window and a couple of flexible insulated air ducts solved the problem quite nicely.

I seem to remember that diesel engines were used on a German WWII transport/bomber (Condor?) (The plane was too lightly constructed to have much of a payload, but it had a lot of range.)