A properly operating cooling system should not have to rely on the protection and intervention of the aux fan. That switch operates at 91C and 99C (196F and 210F). It should not kick on until your temp gauge needle is near those marks.....here is a converted image from Don Gale....



Quote Originally Posted by E34 530
However, I have noticed that the auxilary fan DOES NOT come on even when the needle start to creep past the half way mark. Could the sensor that tells the aux. fan to come on be bad, causing the slight overheat?? .....