MYSTERIOUS OVERHEATING ISSUE

It might be worth checking the grounding of the gauge and the wiring? I had a very similar issue with my new to me 110, the needle on the gauge would go right up into the red looking like it was overheating, but actually the issue seemed to be the lack of earth to the gauge. Not sure how it would've been originally but definitely seemed to sort out my issue adding in a new earth wire to the bulkhead.

The sensors are basically thermistors, and the gauge reads the resistance compared to ground (no resistance). So if its reading higher than you expect there could be more resistance somewhere in the system, potentially due to a bad connection or something like that.

And a brand new black sensor....this is where it went!

and whats the actual temperature? if the dial doesnt match the sensor then it will give a false reading

Changed the sensor .....black for defenders green for discoverys! Engine cold

Why don't you buy aftermarket gauge with sensor and put it in the top hose?
Or capillary gauge if you know what the thread in the housing is.
Saves buying endless sensors which are not compatible.
Have you tried earth on the gauge which someone previously suggested?
By the way even if you do find a sensor which seems to work you still need to check temperature independently to make sure it is correct.
We have fitted two gauges on the 200tdi.

Thanks. The gauge is a pukka LR one from Brookfields. My chum is taking the front end off on monday to check the wiring an fitting an earthing wire. Meanwhile I will drive around without looking at the Temp gauge.... Have checked the top hose and it is not overheating.......fingers crossed!