My knowledge of engines pretty much ends with knowing how to start and stop them. FWIW, I put an oil pan heater on my Cummins 5.9L engine a couple years ago. I didn't have any starting or smoking problems but just wanted to keep the engine warm enough to keep it dry in the wet months. I put a 250W heater on the oil pan and it keeps the engine block temps in the 50's even during sub-freezing weather. It also keeps the rest of the ER from getting too cold.
If you heat the oil pan, heat rises. This keeps the whole engine a lot warmer. I leave the heater on 24/7. Has worked out great. On a really cold day, it does help to bring the engine coolant temps up more quickly, but most of the time it makes little difference.