If you drive it on the street, you definatly need a thermostat of some kind.
Oil has an operating range. If you want it to do all things that
oil should do, it has to be kept in that range. Maximum temp is not hard to find, but minimum temp is. It seem like minimum would be around 180* or so. But some thermostats open at 220*, so an engineer somewhere thinks that's the minimum. Maybe it is, I don't know. In any case, it should be at least 180*.
Some people say that if you don't get the
oil over 212* the water won't evaporate. That's not exactly true. Water evaporates at much lower temps. If it didn't, your kitchen floor would never be dry.
I tried a couple of sandwich type thermostats. Worked great in the summer. Oil temp stayed between 180-190* all the time. In the winter, though, getting the oil warm was almost impossible. Even when I covered the cooler with cardboard and duct tape.
So, I put a separate electric oil pump in, and run that only when the oil gets hot. I was at the track last week and it worked really well. Now the engine oil pump only pumps oil through the engine, just as designed from the factory.
A good option for an occasional track car would be a heat exchanger. In the winter the oil is heated by the hotter coolant. In the summer, the oil is cooled by the coolant. It works to keep the oil and water temp about the same. Ford used that set up on a number of differant cars and trucks.