I have a timer in the outlet for the block heater. When I lived in SW lower MI, I'd have the timer turn on 2 hours before I planned on starting the engine whenever the temp was going down to freezing or below. If it was closer to 0, I'd set the timer for 3 hours before starting. Before I had the timer, I'd plug it in the night before, but that caused a significant increase in electrical usage $$$.
At the time, I was using Rotella 15w-40 oil (not a synthetic or blend). I used the block heater a lot because I wanted to make it easier on the engine, not because I had to use the block heater to start.
Here in AZ, I have used a 'Thermo Cube' that turns on when the air temp drops below 35* and shuts off when the air temp reaches 45*. I've used it a few times, both with and without the timer. Amazon: Thermo Cube Thermostatically Controlled Outlet - On at 35-Degrees/Off at 45-...
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