i am just curious the problem is not always occurring. Why did the radiator fan not functioning during when I am overheating but sometimes ok naman ?!
Try mo i-short ang thermostat switch para naka turned-on lagi ang Aux fan mo. Kung humihinto pa rin ang Aux fan, defective na yan or baka may maluwag na wiring.
Kung hindi ka na nag-overheat by doing so, there must be something wrong with your thermo switch.