water temp gauge?

[califjeff]

I have a 1983 f250 6.9l with a/c.
Last week or so I noticed the temp gauge would read normal them jump up to half way or so and come back down but at night seems to read fine. I heard the factory gauge is crap and to install aftermarket gauge. Also i replaced the sending unit but didn't change anything. and could it be the the thermostat?
Any help would be great thks

 

[Dieselcrawler]

Could be something loose in gauge cluster

 

[snicklas]

Since it is a Slantnose, they have the IVR (Instrument Voltage Regulator) for the instrument cluster. If they stick, all the gauges read high. Did you notice, did all the gauges (Fuel, Oil, Amp, Coolant) all go high and then later go back to normal? If so that is a trait of the Slantnose trucks. Ours did it back in the 80's when it was newer. If it does it again, hit a bump, or lightly thump the top of the dash, I bet they go back where they belong.

 

[califjeff]

it was only the temp gauge, rest read normal. don't want to replace thermostat if I don't have to

 

[icanfixall]

Try removing the sender wire in the drivers side head. Thats the over temp sender and it peggs the gauge when the coolant temp reaches 242 degrees. They are a problem sometimes and cause you to think the temps are way out of range. Removing the wire and running the engine will tell you if thats an intermitnet electrical problem. Another way to test if the sender in the head works is to remove the wire and ground it. the dash gauge should peg well past the hot or the "L" letter. Why don't you want to replace the thermostat??/ You have to remove a few things but its not that bad. Also never install any thermostat thats an after market one. They can't pass enough coolant to keep the engines cool. Many parts stores sell a chinese look alike that will fail. The words "made in china or just chaina" will be seen on the fakes.