How do you fix the thermostat gauge in your 1990 Plymouth horizon The actual coolant valve is operatonal?

To fix the thermostat gauge in your 1990 Plymouth Horizon, first check the wiring and connections leading to the gauge for any signs of damage or corrosion. If those are intact, inspect the thermostat itself to ensure it is functioning properly, as a stuck thermostat can affect the gauge reading. Additionally, consider replacing the temperature sending unit, as a faulty unit can cause inaccurate readings. Finally, if all else fails, consult the vehicle’s manual or a professional mechanic for further diagnosis.