Land Rover Repair: Fluctuating Thermostat Readings, range rover hse, highway speeds

Question
Hello John,
 
My 2002 Range Rover HSE has a problem with the thermostat.  The reading goes into the red when stopped or driving slow.  However, at highway speeds it stays in the middle of the gauge.  While getting the vehicle smog checked, this happened.  The technician at the smog center verified (with a temperature gun) that the vehicle was not actually overheating.  Have you experienced this before?

Answer
Well, some of your data is probably wrong.

The symptom you describe is consistent with a car whose radiator (for example, there are other possibilities) is clogged, and which is overheating in traffic.  

Yet you say the smog tech says it's OK

The up and down of the gauge tells me the smog tech is probably wrong.

I think you should find a qualified LR service person, and have them do a better check.  If the motor overheats and you ognore it, you could put yourself in the way of a $10,000 repair.