Bad Coolant Temp Sensor?

[bmw5002]

Ok I just recently installed a new thermostat and i ran the car up to operating temp. so it would open and i could purge air from the system and top off the radiator with more water or anti. Anyway, I thought it was strange that I didn't hear the fan come on when the temp. guage was about halfway, and it should be at that point. So I ran the car all the way up to about 3/4 until coolant started boiling out into the overflow resivoir and the fan still didnt come on. So I disconnected the wire to the coolant temp. sensor, and whadda ya know, the fans come on. Do you think it could be bad? There is no CEL on either. Why do you think my fans don't go on when needed?

[fredk]

if its the little single blade sensor, its probably bad, kinda common