Ok here is the electrical impaired fix. Take a test light hook it up to the ground lay underneath the dashboard and look for a little metal oblong shape near the center of the dash board. As I recall there's three wires to it but there could be two. This is the power supply to the gauges If you hook up the test light by touching it onto that with the ignition on the light should blink the power supplied is not steady.
Now back to the thermistor.
Get the car to operating temperature go get a under $20 infrared gun and shoot the metal area surrounding your temperature sensor and then compare that to what it says on the gauge. Hopefully this will find your reading is probably on the high side. I have had gauges read 20° to 30°, hotter than reality. Even when I pick the hottest part of the motor back up against the firewall on and shoot it with the IR gun.
Rule no 1 KISS rule no 2 don't take rule no 1 personal
Want to make it harder to understand? Add a volt ohm meter into the process with all its multiple settings and numbers...
My fix was to add resistors in line to the offending gauge in this case the temp sender.
Nearly every gas gauge sender in the cars that I have had have required a pull apart and thorough cleaning of the wires and contacts in the sending unit. Except for one car that was parked since 1977 in a nice dry garage with no gas in it.
