Temp gauge problems

[Usmczo6]

I disconnected my factory temperature sending unit, the gauge inside the truck was very erratic, I put in an autometer in the same location everything works as it should, I took the gauge cluster apart cleaned all of the connections, I figured I would try to see if the original temperature sending unit would work now, it's buried past 260 degrees at all times and it does fluctuate a hair with revving of the truck, is this more commonly a wire issue to the sending unit or do the sending units themselves go bad?

 

[45tt]

I’m in the same boat as you. I’ve replaced the thermostat, temp sending unit and dash gauge. I down to replacing the pigtail and wire. I’m thinking that my wire got to close to the header and scorched it. If that doesn’t work then I’m not sure.

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[1987 GMC Jimmy]

Could be the wrong sending unit with a different resistance range. The engine bay ground network has to be right, or it’ll read wrong. And then the wire can’t be chafed, which you already know. Mine’s set up perfectly, and it sits at three quarters to pegged when it’s warm. I’m eventually going to try a 70 ohm resistor inline and see if it reads right.

 

[Usmczo6]

I'm going to hook the Auto meter back up it looks cooler anyway, let me know how you guys make out

 

[Swearbody]

The sending unit registers resistance. It sounds like it has too little hence the high reading. If its increasing when the voltage increases (revving engine) then it has no resistance. Voltage is flowing through too easily. Probably a bad sender and not a bad ground. Try measuring the resistance from pole to pole on the sender.

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