Canada's Cold Weather Testing Establishment determined that air-cooled piston engine operation at low rpm, i.e. idling and taxiing, is not recommended in surface temperatures lower than -38C. Baffle plates installed ahead of the cylinders reduce the effect of cold air engine blast to a small degree. Potable/fresh water systems should be drained in anticipation of extended below-freezing soaks. Portable electric heaters can be used to warm the cabin.
Typical engine pre-heater in use. Note this Cessna 207A Stationair 8 has anti-gravel protector flaps installed immediately aft of the main wheels.