I have a Sanger flatbottom v-drive with a 327 Chevrolet 1960's engine and Rewarder wet headers. It is run in freshwater only. I bought the boat this summer. When i went to winterize this fall there was no thermostat. I am in Michigan. Is thermostat needed and if so what temp. I tried a search on this site but still can't get a sure answer. Thanks for your time.