Is it likely to be the black temp sensor? There are the two sensors on the front of the head, on the water flange, one blue, one black. The blue is for the ecu, and the black is for the dash gauge.
The black sensors seem to read low with age, I just fitted a new sensor, and now the needle sits near half at normal running temp (it used to only get that high when the fan was coming on)
So that may be worth replacing. looking at my reciept from vw the blue and black sensors were £13.37 and
£19.22 inc vat, duno which is which tho! (part no's 025906041A, 251919501D) May be worth getting genuine, as reports indicate aftermarket blue sensors are not as good, so same probably goes for black....