My $22/pair oil pan stick on heaters arrived. They seem decent enough quality. About a 6' cord. They are supposed to be thermostatically controlled to 194F within a minute of power being applied. With 150w they should heat up the oil like mad. Much faster IMO than 400w cartridge heater trying to heat coolant via air convection through the aluminum to the coolant.
I plan, when installed, to record the heat the engine has when the oil has been heated for 30 minutes, 1 hour, 90 minutes and so on. I suspect strongly that it will take no more than 30 minutes at -30C to heat all the oil to 194F. If I can heat 2l of water in my kettle to 212F within 2 minutes at 70F ambient heating the oil should be as efficient and fast.
Bonus!! The silicone pads will make an ideal heater for my build plate of my 3d printer when I'm working with material that requires constant hi temps not to crack or warp. One material I have in mind wants a build plate temp of 200f. Perfect.