> They've been used since forever to heat and start large engines. Depending on size the pony motor might even produce enough heat when idling to keep the crew cabin warm while you service the main engine.

The much larger problem is that the engine will have seized by the time you're done. In central siberia (oymyakon and friends) locals will keep the engine running from when they leave home (having possibly heated it up by starting a fire under the engine block to thaw it) to when they're back so it doesn't freeze solid. Even the gasoline will start coagulating at the temperatures involved.

Gasoline (I'm not a petroleum engineer so I make no claim about certain additives) is fine down to any earthly temperature. It was used extensively in 1930s antarctic expeditions for this reason.

The pony motor can be heated with a gasoline blow torch (yes that's a thing) to start easily. Then it can heat the coolant (and through that coolant the oil and cylinder heads) of the main engine so that the main engine may start easily. Depending on the size of the pony motor it may even be able to provide cabin heat.

My friend from Alaska took him about 20 years and his wife putting her foot down to give up on the white gas stove for that reason.

Diesel trucks often have a diesel powered coolant heater and pump for that reason as well. Turn on the heater and you can shut down the engine knowing it'll start again. And so you still have cabin heat.

See random sales website.

https://www.webasto-comfort.com/en-us/heating-solutions/off-...