Maybe the gauge is broken... Any signs it is really getting hot?
First thing I would check is the cooling fan viscous unit. They have a high failure rate. When you have gotten too hot, it should be locked up. Carefully try and slow it down with a rolled up newspaper. If it is working, you won't be able to slow it down.
Pissing people off on the "net" since 1983.
Land Rover. Turning owners into mechanics since 1948.