Hi my engine coolant temperature sensor does not give a reading on my code reader. But the dashboard temp gauge works.

I also get some engine hunting when cold , thought it was gearbox which has now had an oil change, or throttle body. But now thinking it may be running rich as I only get 30 uk mpg on a run.

Any thought on why the gauge works but the ecu appears to have no reading of temp?

2003 x350 3.0l petrol UK