Nissan 21200-0B000 Thermostat Assembly

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2000 and later models are equipped with a water control valve in addition to the thermostat. The water control valve is mounted on the water outlet pipe assembly at the rear of the cylinder heads and connects to the cylinder block. Before assuming the thermostat is responsible for a cooling system problem, check the coolant level, drivebelt tension, and temperature gauge (or light) operation. If the engine takes a long time to warm up, the thermostat is probably stuck open and should be replaced. If the engine runs hot and the upper radiator hose is not hot, the thermostat is probably stuck closed and should be replaced. If the lower radiator hose is hot, it means that the coolant is flowing and the thermostat is open. A more thorough test of the thermostat can be made when it is removed from the vehicle. To test it fully, suspend the thermostat in a container of cold water and heat the water while observing the temperature and the thermostat. Note the temperature when the thermostat begins to open and when it is fully open. If the thermostat doesn't open and close as specified, or sticks in any position, replace it. To replace the thermostat, disconnect the negative cable from the battery and drain the coolant from the radiator and engine block. Remove the necessary hoses and components to access the thermostat. Remove the thermostat cover and the old thermostat, then clean the housing and cover. Apply a bead of RTV sealant around the perimeter of the cover, install the new thermostat, and bolt the cover in place. Wait for the sealant to cure, then refill and bleed the cooling system. To check the water control valve, perform the initial steps of the thermostat check. Note that the water control valve is fully open at a temperature above boiling, so you won't be able to see full opening of the valve in boiling water. To replace the water control valve, disconnect the negative cable from the battery and drain the coolant. Detach the cylinder block hose from the water control valve cover and remove the cover and gasket. Remove the water control valve from the water outlet pipe, clean the pipe and cover, and install the new water control valve and gasket. Reinstall the cover and hose, refill and bleed the cooling system, and check for leaks and proper operation.

After installing the new thermostat, you should tighten the thermostat cover fasteners, reinstall the hoses, and wait for at least 30 minutes for the sealant to cure. Finally, refill and bleed the cooling system, and run the engine to check for leaks and proper operation.