Back when I lived on a barge, and needed to motor to get water, I had a starting problem. Big diesel, very cold weather (it was cold back then, children) = = flat battery. No way of charging said battery either.
It was a raw-water cooled engine (water pumped from river round the engine block). I added a bit of plumbing so that the barge hot water (gas heater) could be routed around the engine. Two min of running that filled the engine jacket with water at about 70C, warming it up nicely. Started instantly.
This amazed all other boat owners, who struggled with starting in winter.