Land Rover Repair: 1999 LR Discovery II - Thermostat Failure, coolant temperature sensor, failure symptom

Question
Symptom: At the beginning of the day, without warming up the engine, the water temp gauge get's stuck in extreme low position and sometime the light becomes lit. The after mile or two, the gauge becomes normal and the light is OK. I'm wondering if this is a faulty instrument or sticky thermostat. Mileage of this SUV is 55,000 miles. Radiator was replaced at about 30K. Thank you

Answer
You haven't identified the light that lights up, but I presume you are talking about the red overheating warning light on the end of the temperature gauge.  This will illuminate if you have a bad coolant temperature sensor.  If the vehicle has been overheated and the codes were not reset, a low coolant level will also cause the symptoms you describe.