Join Date: Sep 1998
Location: Cleveland, Ohio
The coolant sensor is basically a variable resistor, that changes resistance with heat.
If your vehicle has the correct temp sender, then find out what the resistance spec is at a specified temp (Autozone has a book that lists many different temp senders, and there specifications), and replace the temp sender with a basic carbon comp resistor. For example at 220 degrees the resistance for a particular sender might be 10K ohms. Then find a 10K ohm resitor and put that in place of the sender (make sure the correct wattage resistor is used). The gauge basically reads the voltage drop across itself, which changes as the resistance of the sender changes. This test should verify the gauge and associated wiring.