Assuming you are talking about the factory temperature gauge fitted 1967 on, (and the part numbers confirm this) then the problem is most likely that the voltage stabiliser is :-
1. Missing or not in the circuit
2. not properly earthed (on this model it is mounted on the bulkhead and relies on the mounting and the bulkhead for earthing)
3. Faulty.
(in that order)
The voltage stabiliser gives 10v nominal, but this is actually an intermittent 12v switched on and off by a bimetal strip with a period of several seconds.
If the stabiliser is present and working (confirm by switching on the ignition and check voltage at the sender, should go on and off, also is the fuel gauge behaving), you may have a problem with manufacturing tolerance of the gauge and/or sender. I had this, so the normal running temperature was only just below the hot mark. I simply experimented with small resistors until I found one that gave the normal reading when in series with the sender.
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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