Hi Jono,
All Beta gauges are notorious for odd and incorrect readings, although strangely,
they seem to continue functioning in some manner or other.
It may be worthwhile renewing the sender unit in the head, these can also give
erroneous outputs.
Also consider obtaining a generic temp gauge as a temporary test device.
If there's no signs of overheating, and the fan is cutting in after the thermostat has opened,
it's probably ok. I really understand, though, that a bad indication is just not wanted.
Regards
Nigel