Defender 90 with 300 TDI Temp Query

Have just been to look at a defender 90 that has had a 300 TDI engine fitted from a Discovery and the temp gauge reads about a quarter of the way accross upon start up and runs into the red when warm, it has a disco sensor and a defender gauge, is this why its reading hot and is the fix to fit a defender sensor to the disco engine.?? Or am I barking up the wrong tree and could it be a more serious problem??

Regards Andy

YES - You need to match the senders and guages. When I went from an NA to a 300tdi it did exactly the same, I bought a 300tdi DEFENDER temp sender and screwed it in, 5 min job and that's it done.