blondejay;68138 wroteFunny enough though, on the hot days here in melb, 35+ hitting the freeway sometimes with minimal traffic, I've seen my Led (trigger light, connected to the pull fan) light up for almost the entire 40min drive. This tells me that during high ambient temp low rpm, high air flow driving conditions that the coolant temp can not get below my fan sensor set temp of 85deg.
At freeway speeds the fans windmill and generate power, so if you have your indicator LED wired to the same pole of a SPST relay as the fan motor, the LED will light as a result of that current flowing.
To avoid this, I used a DPST relay with the motor wired to one pole, and the light (I was using a bulb) to the other, this way they were electrically separated when the relay was open. Using a bulb, I could watch it begin to glow faintly at about 70km/h, and get pretty bright at freeway speeds!
I've never seen any of my electric fans come on above 40km/h, even in very high ambient temps.
Upper or lower hose sensing methods both work well, as long as the switches are suited to the location. The setup on my 760 uses a sensor in the head and an adjustable controller, and holds the gauge needle rock solid under all conditions, and doesn't cause the fan to run for very long or too frequently at idle.
Note that virtually all OEM applications use sensors in the head or thermostat housing.
