1996 Range Rover. The engine is not overheating but the temperature gauge goes to red. when you speed up it returns a little.

Had a same problem and it turned out that the water pump was on it's way out and leaking coolant. It wasn't leakoing badly but just enough to trap air in the system and cause the temperature gauge to go crazy. Replaced the water pump and radiator and since then have had no problems and temperature sits in the middle. This was on a 4.6 v8 1997 HSE

I have the same prob. but with mine if I turn on the headlight the temp goes to red, if I turn the lights off it will still stay high. If I turn the engine off and start again it will stay in the green. It seems to me that this must be an electrical issue.

Mine used to have the same problem, same with darius over there the water pump is leaking and air got stuck in the coolant reservoir, so open up the cap a little so it can breath a little