I actually find the gauge quite accurate, mine usually stays around the R then on cooler days it runs around the M when driving along, fans kick in between the M and O.

If you have fitted an aftermarket radiator you need an uprated fan switch otherwise the fans stay on due to the heatsink effect, these switches are far superior anyway with a better span bringing the fans on at a higher temperature and only a few degree span opposed to the OE 86 degree and off at 77 some 11 degrees!

I have a standard radiator and suffer from the same problem with the standard switch, trouble is they sap so much power and it will end up melting the fuse etc very soon.

Martin