Looks like Vera's thermo fan is dead, it's always done the same thing my old TH did go over the half way mark but it always went further over. Well today in the heat I got a bit concerned so I parked it up and tested it and the right side A/C fan works with a two speed but the left side fan is doing nothing.

I'll take it to the auto elec tomorrow unless someone else has a better idea ..... and Mals too far away.

Had the same problem with a '99 TH - the low speed part of the fan failed - ended up jumping the Low speed relay input to the A/C fan input and that kept the car cool...