Erratic Gauges

Case in point 73 Valiant ( no oil gauge). After engine was at running temp, turn engine off, 10 minutes to go in the store whatever, then turn switch back to on, temp needle would race to 'H' then fall back to normal reading while fuel gauge never did anything out of the ordinary. So the only time I saw a wild needle swing was with hot water. Faulty mechanical limiter was the problem. Solid state regulator cured it.