Hello, granted this is a boat, although it is a 1977 Ford 302 motor. All of sudden Temperature gauge fluctuates when not running. or has not been even started..
Has Steward Warner Gauge. Had it 20 years.

Just turn the key on. and gauge goes to 240 , drops down to 140. goes to the middle of gauge. Bounces back and forth all over. Wiring is tight on gauge and sending unit. .tap on the gauge doesn't have effect. Any ideas?
Thanks Mitchell

 

A good part of the time when we get incorrect or intermittent info even though connections appear tight there could be a corroded connection in the circuit. Have you considered loosening and cleaning the connections and also applying some dielectric grease to the connections to help prevent moisture induced corrosion.This is always a good first step and may be all that is required to get rid of the problem.

 

Hello, thanks for the quick reply. I am able to clean and check connections on gauge, and sending unit today. Let you know. Thanks.

 

I cleaned the sending unit, took it out, cleaned the terminal, Same. Although when I run it seems steady not like before bouncing all around. Yet to clean the conections on the guage. I did touch the sending unit wire to ground guage goe to peg 240 holds steady, then off and drops to below zero. Still checking. Although cleaning connections seems to had some positive effect. As before when runing it would jump all over.

 

Sounds like you're on the right track.

 

Update on Temp Guage erratic reading. After cleaning all terminals, guage, and sending unit, no real change. Grounded wire guage was steady.
Finally installed new sending unit. Stweard Warner brand $40.00. Guage now behaves properly.
Thanks.

 

Thank you for the update.