I am a believer in preheating an engine when it is below freezing. pour oil out of an oil can sitting outside below freezing and one that is at room temp, there is a big difference in flow.

the metals of the engine itself will have tighter ,closer tolerances by the low temps .

I use a reiff 150 watt preheat system , at -15 C / 5 F it takes 4 hrs plugged in to get these pre-start temps: 67F CHT's ,57 F EGT's, oil 63 F, coolant 44 F .

I usually plug it in to a timer and give it a minimum 5-6 hrs of preheat before planned flight, temps are usually in the 80's F before prestart.

unheated hangar, cowl cover, reiff preheat 150 watt are the conditions.