If I am using the cluster temp gauge for diagnosis,the first thing I do is check it for calibration..As Jon said, you would be surprised how many are off and you don't want to be chasing your tail off on the assumption your gauge is correct.

Ohm the sensor unit to verify the gauge reading.

OHM 110 = 60C
67 = 80C
38 = 100C

I have a simple , homemade , known value , 38 ohm Resistor [ RS item, < $1] with plug on it in my toolbox..I sub. that for the sensor and look at the gauge for 100C...Simple ..