[stephen low]

There is a sender on the water pipe that leaves the pump heading to the heater. Do I assume this is feeding info to the ECU on temp?

If so what drives the thermo fan operations?

I have had suggestions for various sensor locations on the raditor. Measure heat in at top of radiator ie temperaure as leaving the motor versus heat out of radiator near outlet showing return water temp back into the motor.

I'm probably stuck with maintaining a sensor on the radiator but it is whether it is near the inlet or outlet location.

Suggestions on those choice please?

Running the engine on idle up to 100C the other day didn't fire the thermo with a sensor set to 92C on 87C off switching. Short circuited the wiring and the fan came on and it also activated using my over-ride switch so the system is capable. Might have to do a boiling water test to see if the switch is ok first.