Engine Coolant Temp Sensor
It's the sensor that talks to the ECU and then the ECU decides when to turn on the fan.
The 1.8 cars are completely different than you 1.6 car.(Tim) If the sensor is giving wrong data to the ecu, than the ecu will not turn the fan on....
BTW, good job trouble shooting. I'd send you a beer, but It would be warm. I'll just drink one for you instead