If the coolant temperature gauge is inoperative, check the fuses first. If the temperature gauge indicates excessive temperature after running awhile, troubleshoot the issue. If the temperature gauge indicates HOT as soon as the engine is started cold, disconnect the electrical connector at the coolant gauge sending unit and if the gauge reading drops, replace the sending unit. If the gauge fails to respond, the circuit may be open or the temperature gauge may be faulty. To replace the sending unit, drain the coolant, disconnect the electrical connector for the sending unit, using a deep socket or a wrench, remove the sending unit, install the new sending unit, and tighten it securely, connect the electrical connector, refill the cooling system and check for coolant leakage and proper gauge operation.