Preferred Coolant Temps

ValiantS said
You'd want the oil over 220-260f and the coolant about 33f but neither are realistic. So, if your chasing a tune-up keep oil temp consistent and near 200 and settle for the coolant temp at a reasonably achievable LOW value.

Oil temperature is based on clearance and grade. You run a 0w20 oil at 260 and it will kill the bearings.

Cool temps and thin oil makes more power in gas. Alcohol based fuels are different