Oil temp gauge issue

[Nine One One]

Wire it up as in the link, put it in boiling water and see what it reads then, at least you have a bench mark as to how accurate it actually is, and it will also show you on the gauge where 100 degrees C is, which may give you some peace of mind whilst you drive it, and try and sort out another sensor.
Whilst it is out you can also measure its resistance.
Have you tried PRS or Tuthills for a sensor? They probably have better knowledge of what sensor goes with what gauge/year which should be dated on the back of the gauge?

[Hugo 356]

The currently available new 6v senders have a diferent calibration to the originals. You need to have the guage re-calibrated to match the current sender or better still get a working old sender

To add I was referring to these senders:
https://www.rogerbrayrestoration.com/sh ... re-calibr/

Not sure about these:
https://www.rosepassion.com/en/diagrams ... 80501-9516