As a data point, I have E-Z HEAT 912 engine pre-heater which consists of two silicone heater pads – one for bottom of crankcase and the other wraps around bottom of oil tank. I have a remote cellphone relay switch so I can turn unit on well in advance of engine start. If OAT is 20-30F I’ll pre-heat for 180 minutes. When I arrive at the airplane the oil and water temps are 80F and I’m good to go.
Hi Pat. I developed the first oil therm ( using Thermostassis ), and it has been great. It cuts down warmup time by a bunch. I can start engine, and start taxiing right away, and be at needed temp before I get to end of runway. ( over 1/2 mile for me ). I would rate this as my second best invention. The "Heater Damper Door" is best/first for winter flying.