In order to troubleshoot an inoperative coolant temperature gauge, test the fuses first. When the gauge shows that the temperature is too high after a period of time, then more research is required. In case the gauge indicates HOT as soon as a cold engine has been started, unscrew the electrical connection at the coolant gauge sending unit that is installed in the engine compartment. In case the gauge value decreases, change the sending unit; in case it stays high the wire leading to the gauge can be shorted to ground or the gauge can be defective. When the gauge does not indicate any reading after letting the engine warm up during 10 minutes and the fuses remain unbroken, disconnect the electrical connector at the sending unit, and momentarily apply a jumper wire to a clean ground on the engine. In case the gauge reads HOT, change the sending unit. Resistance can also be tested using ohmmeter, the sending unit should show resistance of 190 to 260 ohms when there is hot engine coolant and when the engine is cold. In case of non-response of the gauge, one may open the circuit or the gauge may be defective. To replace, remove the coolant, disconnect the wiring connector of the sending unit and remove it with a deep socket or wrench. Install the new sending unit in place and do not make use of thread sealer, re-connect electrical connector, divide the cooling system and ensure that there is no leakage of coolant and gauge is functioning properly.