A couple of thoughts regarding preheat. Consider them in your conditions, dismiss them, I don't care. I'll just share what I've learned through 20+ years of Alaskan winter flying.
Warm air, no matter how it's applied, will quickly heat cylinders but oil takes a long time. Especially since the heat transfer from heater to oil is very inefficient. I've used hot air in the form of Red Dragons, mini Herman Nelson setups, and probably the best option, a 900w "Little Buddy" electric heater mounted on my engine mount with adel clamps. Include my ammo box combustion heater, too. In all cases it takes time to preheat an engine properly. Almost nobody allows enough time. The cylinders feel warm and they get impatient so they pack the heater and start the plane. In below zero temps it's easy to heat the cylinders enough to quickly fire the engine for but if the oil isn't warmed the oil pressure will sit on zero for many seconds. Maybe 30 seconds. That sucks. There has to be a better way.
Oil pan pad heaters are cheap and effective. A 75w pad heater will warm the oil well when attached correctly to the sump. Yep, it's an electric appliance so power is necessary. If you leave it on all the time the greenhouse effect takes the water vapor to the place where dew point occurs and the humidity condenses there. Like in your cylinders and on the cam and lifters. Most of us will only preheat prior to a flight so the time factor is important. In cold temps, even with a well insulated engine cover, the oil can be warmed to ease the starter's work in turning the engine but the cylinders, being engineered to air cool, may still be cold. Prime it, hear a few ignition pops, and sometimes all you get is frosted plugs. That'll postpone your flight. Nothing to do now but break out a real heat source and warm the engine thoroughly. So pad heaters aren't a great solution either.
Enter Tanis and Reiff. These guys heat the oil and the cylinders. Tanis has an option to heat the case but that'll happen coincidentally when the oil is adequately warmed so I think that's a waste. I remember an 18* day when I put a generator to my Turbo XP system on my then new Cub. In about 3 hours (I left and came back) the oil and cylinder temps were at 90*. I don't know of a more efficient or practical way to heat an aircraft engine. Sometimes I have to use warm air from a combustion heater but I never prefer it if I have an electric option. A heater like the Little Buddy works well but it'll take considerably longer. Like overnight. In concert with an oil sump heater it's faster but it'll require more than a 1000w. No big deal for a power outlet but not too practical for my generator. Reiff and Tanis apply good heat with small power consumption. My Reiff system allows me to dedicate less time to airplane prep. That's a important detail in my life.
The coldest temps I've flown in were just shy of -40*F. Prepping a plane is not fun in those temps. Nothing is fun in those temps. Preheating is a slow process and heating too quickly is a real concern. Using a combustion heater forces me to stand there and monitor the flame. Been there, done that. Don't want to do it again. I'd rather carry a generator if I anticipate those kinds of temperatures. Start the gennie and go back inside for coffee or a nap!
