I just bought this 85 f250 with s 460 in it and the temp gauge is reading almost all the way hot after warm up. The owners before me put in a new radiator. I changed the thermostat temp sending unit flushed the radiator which is full of brown liquid no matter how many times I flush it. and am currently changing water pump. The old one didn't seem to be in bad shape but I went ahead and put a new one on. I am almost done putting it all back together but I don't think the new water pump will change anything. When the temp gauge is reading hot the coolant in the radiator is barely luke warm. Shouldn't it be boiling if it's that hot?My oil gauge is also reading high even after a fresh oil change. Are my gauges junk? I'm completely stumped.

 

This goes back a bit and it will require you to check it out.
There was a small component called a voltage regulator mounted on the rear of the instrument cluster. It provided 6 volts to the gauges for them to work. Sometimes they would quit working, but I don't believe that is taking place here, it may be providing the wrong voltage to the gauges. Some later years used the temp gauge to provide the correct operating voltage. You might use a voltmeter to check this out. The voltage regulator was about a half in thick by an inch and a half long and was silver colored held in place with one screw.

 

Thank you I will look into this. One question though. Since when I start it up cold the theme reads cold and gradually moves all the way to Hot. One time it stayed in the middle for a few seconds and then started rising. Would it be doing this if the Voltage regulator is bad? Basically the only gauge that is reading good is the battery gauge. Gas gauge seems to fluctuate oil rises to the top emediatly and lowers a little when warmed up. Temp gauge reads hot even though the Coolant is barely warm

 

It might be a good idea to check the grounds going to the sheet metal of the cab. If there is a poor ground it will go through the gauges and cause them to read higher than normal. You might try disconnecting the oil or temp sending unit wires at the sending units and see if that makes any difference.

 

New and first post: One of the easiest troubleshooting tools to use is a digital non-contact thermometer. Use one to measure the temperature of the radiator top/bottom, thermostat housing and intake manifold next to the thermostat housing and the sending unit. If you cannot measure it then you cannot troubleshoot it, you can only guess. I don't like guessing. I have a '85 F-250 4x4 with a 460 and upgraded to a brass radiator. Aluminum core is fine until the tanks rupture. I also prefer mechanical gauges so I have a 3-hole housing on the top of the dash for mechanical oil and temperature gauges. Third is the fuel gauge.