You should run a thermostat on the street. Normally, engines run best at a specific temp ( usually 180 to 200 ). Running on ether side of that range can cause multitides of issues, and none positive. Running a stat will get you in to that most efficient operating range as quickly as possible and help keep you there. Running without a stat will not cause immediate damage - un less you go in to major over-heat ( which can happen ).