I also believe I need one as well. But if you didn't have a thermostat in your engine, that is not your problem. I understand that without a thermostat your engine should be running as colds as possible. The thermostat only regulates water-flow to keep the engine running at 180 degrees or warmer. Basically it stops the water from flowing when engine temperature is below 170 degrees. When engine is above 180 then the thermostat is supposed to be fully open. If you dont have a thermostat, then that means that water flow is flowing at its maximum flow rate and your problem is most likely not the thermostat but possibly a water pump or clogged water system some where.
I'm not a mechanic but can anyone confirm my belief above ??
The reason for thermostats is to keep the engine running warm enough... If we never had a thermostat, the engine would run way too cold and cold means bad fuel economy and bad efficiency.