Hummer 12600171 Thermostat Unit

Before assuming the thermostat is to blame for a cooling system problem, it is important to check the coolant level, drive belt tension, and temperature gauge (or light) operation. Before starting the replacement process, it is important to disconnect the cable from the negative terminal of the battery and partially drain the cooling system, saving the coolant if it is in good condition. If the fitting that mates with the hose deteriorates, replace the thermostat housing. The thermostat housing can be removed by removing the bolts and tapping it with a soft-face hammer if it is stuck. The mating surfaces on the engine and the thermostat housing should be cleaned, and a new O-ring should be installed in the groove in the housing. The thermostat housing should then be reattached to the intake manifold or water pump housing, depending on the model, and the bolts should be tightened to the proper torque specifications. Finally, the cooling system should be refilled, the engine should be run, and carefully checked for leaks.