Originally Posted by vyper developments

Hi All,
I have owned the same 2WD sapphire for nearly six years now and have replaced the temp senders on quite a few occasions. I have found that there is a big discrepancy over the resistance values of the temp senders, these senders work on a NTC principle, which means that as the water temperature increases the resistance decreases and this will obviously effect the overall reading of the temperature gauge.
I had the same one in the car for a few years and that one used to read between the N & O of NORM the next one read a bit below that, The current one I have fitted now reads a lot higher at between R & M.
For peace of mind I have very accurate additional temperature monitoring which covers all my engine parameters. The water temp in the cylinder head is around 85 degrees C in normal use, give or take a few degrees on thermostat operation. When sat at idle the fans will cut in at 96 degrees C and will trip in and out quite frequently if sat in traffic.
Personally I think it is wise to have another means of keeping an eye on water temp if you dont trust your standard temp gauge, bearing in mind an increase in water temperature will also affect your engine oil temperature!

CheeRS, Mike.