Dino oil is long-chain molecules and acts as an insulator.
A synthetic oil could possibly transfer heat at an acceptable rate to function as a coolant. It would have to be very thin in order to be pumped properly at sufficient volume. I have never heard of it tried, though it would be interesting for sure.
There are plenty of industrial temperature control valves that you could adapt in-line with your coolant hose/bypass system in order to maintain a much higher operating temp.
Temperature Valve diverts and mixes fluids., Rostra, Vernatherm Div.
