Nope, never got to the bottom of it. the gauge has read high since I got the car, and since then it's had a water pump, 2 new rads, a replacement fan clutch then an e-fan, a thermostat, and a replacement gauge and sender, and it still reads high. It never overheats, so I've just come to regard the high reading as 'normal', either a) it just likes running slightly hot or b) the sender wire has developed a higher resistance with age.