radiator fan problem Options

[johnnybravo04]

Very unusual problem with a 1998 gt . My car was runninig hot and i pulled over and sure enough my radiator fans were not coming on. I replaced the relay to fan # 1 and same problem still accured. Next I checked the engine coolant temperature sensor located on the lower portion of radiator and when the ignition is on and the sensor is unplugged the fans come on. I then replaced the coolant temperature sensor
and the same thing happened. If sensor is plugged in the fans will not come on but if it is left unplugged the fans run constantly as long as the ignition is on. Does anyone know where the problem might be. Also does anyone know if it is fan #1 fan #2 or fan #3 relay that controls the radiator fans. Tahnks for the time and help it is greatly appreciated

[scothaniel]

Next I checked the engine coolant temperature sensor located on the lower portion of radiator and when the ignition is on and the sensor is unplugged the fans come on

The circuit is working properly then. Its actually more like a switch then a sensor, providing a ground to the relay which keeps the fan OFF. Once the temps go beyond a set limit, the sensor brakes the ground connection, turning the fan on. Its kinda backwars to the way you'd normally hook up a relay, but its designed so that if something fails the fans stay on. So the sensor may be bad - you can check it using a little hot water and a continuity tester.

Since the fans come on when the sensor is unplugged, you know the fan itself if fine. It also rules out the relay.

So if the fan isn't turning on, and tif he sensor in the radiator is good and thinks the water is not hot, perhaps the thermostat is stock closed and not allowing the cold water from the radiator into the motor? Or perhaps a clog somewhere, keeping the water from circulating.