Land Rover Repair: 1998 Discovery running hot, coolant temp, fan clutch

Question
John,

My '98 Discovery is running hot, or so it seems, with no other symptoms. At first, it was heating up only at stoplights, etc. So I replaced the fan clutch as I knew my electric fans are running and it would settle back down once I got moving. I did notice something tonight, though - the temp gauge on the dash goes straight to about 1/3 of the white area as soon as the truck is turned on, even after sitting for some amount of time. Then, when started, quickly rises to about 2/3 of the white area, sometimes as high as the top white line, and just hangs there. Have you ever known of a coolant temp sensor to fail in a way that changes it's displayed range?

I can shut off the engine when the gauge is showing high, or top of white range, and slowly remove the coolant reservoir cap without any bubbling over or hissing, or anything of that sort. In my experience of over heating cars, that goes against what I have seen before and almost makes it seem like it is not in fact overheating.

If I were to go so far as aiming a digital thermometer at it, would you have a suggestion as to where to point it and what temp to expect? Any other thoughts or suggestions?

Thanks,
Michael

Answer
I recently had the experience of getting four new temp sensors in a row for an older Rover.  All did what you say - read partway up when cold and all the way hot at normal temp.  Shoot the top of the motor where the sender is located (near the thermostat)   If you read 180-195 the temp is normal.    If you read 220 it's really over hot.  

I ended up solving the problem with the truck here by getting a new genuine sender and putting 50 ohms in series with the sender.

No idea why this has happened