That motor takes a 180 degree thermostat, so if you put the hotter sensor on it, your fan will probably run all the time, because the engine won't be cooled down enough to close the thermostat.
If you put the lower temp sensor, it will only run when the thermostat is open, which means the engine *needs to be cooled. Therefore I'd choose the On at 186 - Off at 161 sensor.
