Infiniti 21200-31U03 Thermostat Assembly

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Before assuming the thermostat is to blame for a cooling system problem, check the coolant level and temperature gauge operation. If the engine seems to be taking a long time to warm up, the thermostat is probably stuck open and needs to be replaced. If the engine runs hot, check the temperature of the radiator hose that leads from the thermostat to the radiator. If the hose isn't hot, the thermostat is probably stuck closed and needs to be replaced. Don't drive the vehicle without a thermostat as it may result in oil sludge, excessive exhaust emissions and higher fuel consumption. If the inlet radiator hose is hot, it means that the coolant is flowing and the thermostat is open. To replace the thermostat, disconnect the cable from the negative battery terminal, raise the vehicle and support it securely on jackstands, remove the engine lower splash shield, drain the cooling system completely, remove the engine cover, remove the air filter housing and intake duct, remove the coolant reservoir and any water pipes that lead to the oil cooler that are in the way, remove the left (driver's) side intake valve timing control cover that is mounted to the timing chain cover and in front of the thermostat housing, squeeze the tabs on the hose clamp to loosen it, then slide the clamp several inches back up the hose, detach the hose(s) from the thermostat housing, remove the thermostat housing cover fasteners and remove the housing, remove the gasket from the engine block and discard it, clean all mating surfaces before beginning any reassembly, install a new gasket, the remainder of installation is the reverse of removal, tighten the thermostat housing cover bolts to the torque, reattach the hose(s) to the housing cover and fitting(s), then tighten the hose clamp(s) securely, refill the cooling system, start the engine and allow it to reach normal operating temperature, then check for leaks and proper operation.