Originally Posted by
Karl @ FPT
It does sound like a faulty gauge or more likely a poor connection, possibly to the back of the clocks, could even be the wire is damaged in the engine bay as it see's a lot of heat over the years making it brittle.
Tried re-wiring it. Must be a faulty gauge. (no doubt age related)
Got myself a VDO water temp gauge and sender plumbed in to give me a more accurate reading.