Derale 18748 Basic Single Stage Fan Controller

I purchased 2 of these to replace a high amp 2 speed fan controller that was malfunctioning. I installed these to 2 separate high amperage relays because the high current the fan uses is too much current for the fan controller switches to be directly connected to the fan. I think because of the low current demand on the18748 fan controller switches that it takes to actuate the relays, that, the18748 fan controller switches should last longer than they would controlling any electric radiator fan because there is far less current going through the switch contacts just to actuate a relay compared to running the fan directly. For the low-speed fan switching I placed one of the probes just below the radiator tank near the inlet. It works exactly as it should. The engine temperature gauge never goes above 200°F before the fan low-speed switches on. Low speed fan switches on most of the time when the engine temperature is at about 195°F, (testing was done with choke all the way on at a medium/high cruise speed RPM; approximately 2900 RPM. The 8748 fan controller switch shuts off when the engine temperature is between 185°F and 175°F as tested. The engine temperature readings that the 8748 fan controller switch comes on and shuts off at does very depending upon driving conditions. It is January winter time so because of the low temperatures, the high speed fan mode has not been needed. I did use a heat gun on the high speed fan switch which I located further away from the radiator inlet and a little bit lower away from the radiator tank just to be sure that it does work. I have a 3rd 8748 fan controller switch that I purchased previously that is also connected through a relay that controls a smaller fan so that when the engine is very hot and I parked it, that small fan will come on and prevent a boil over condition. Conclusion: The 8748 fan controller switch is a very good dependable product and does what it is supposed to do as advertised.