First off, we've done some comparisons on locations for the sensor, and the heater hose is not accurate. It tends to run hotter due to the proximity of the exhaust manifold. Up front gives you a more accurate reading. That said, I run with a thermostat, but with the guts removed. You get some restriction that way, but the water always flows. I know some SM guys run without anything, but I learned long ago that there is not enough heat removal in the radiator when the flow is too fast. With the KOYO, it might not matter......