The reason you should ALWAYS run a thermostat is to ensure the rear of your engine block gets exposed to cooling water.
With the thermostat and temperature gauge located at the front of the block, removing the t-stat causes the cooling fluid to be pulled back into the radiator (recirculated), which results in water only circulating through the "front" of the engine. The t-stat "cycles" to ensure cool liquid is forced to circulate over the entire engine (front to back).
