Nissan 21200-V7205 Engine Coolant Thermostat Radiator

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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 (as indicated by the temperature gauge or heater operation), the thermostat is probably stuck open. Replace the thermostat with a new one. If the engine runs hot, use your hand to check the temperature of the upper radiator hose. If the hose is not hot, but the engine is, the thermostat is probably stuck in the closed position, preventing the coolant inside the engine from traveling through the radiator. Replace the thermostat. Caution: Do not drive the vehicle without a thermostat. The computer may stay in open loop, and emissions and fuel economy will suffer. If the lower radiator hose is hot, it means that the coolant is flowing and the thermostat is open. Consult the Troubleshooting Guide for further diagnosis. A more thorough test of the thermostat can only be made when it is removed. If the thermostat remains in the open position at room temperature, it is faulty and must be replaced. To test it fully, suspend the (closed) thermostat on a length of string or wire in a container of cold water, with a thermometer (cooking type that reads beyond 212 degrees F). Heat the water on a stove while observing the temperature and the thermostat. Neither should contact the sides of the container. Note the temperature when the thermostat begins to open and when it is fully open. The number stamped into the thermostat is generally the fully open temperature. Some manufacturers provide Specifications for the beginning-to-open temperature, the fully open temperature, and sometimes, the amount the valve should open. If the thermostat doesn't open and close as specified, or sticks in any position, replace it. Replacement: Disconnect the negative cable from the battery. Drain the coolant from the radiator. Detach the upper radiator hose from the coolant outlet at the intake manifold and the radiator, then unbolt the hose clamp at the timing belt cover and remove the radiator hose. Detach the bypass hose from the thermostat cover, then remove the cover from the engine. Be prepared for some coolant to spill as the gasket seal is broken. Remove the thermostat, noting the direction in which it was installed. Scrape off any old gasket or sealant on the thermostat housing and the thermostat cover, then clean them with lacquer thinner. Apply a bead of RTV sealant around the perimeter of the cover, install the new thermostat with the jiggle valve UP into the housing, and bolt the cover in place within 5 minutes of applying the sealant. Installation is the reverse of removal. Tighten the thermostat cover fasteners then reinstall the hoses. Wait at least a half-hour for the sealant to cure. Refill and bleed the cooling system. Run the engine and check for leaks and proper operation.

To replace a thermostat, follow these steps: Disconnect the battery's negative terminal and, if applicable, remove the lower engine cover. Drain the coolant from both the radiator and the engine block. Remove the engine cooling fan, air cleaner, and air intake duct from the engine compartment. Disconnect the upper radiator hose from the coolant outlet at both the intake manifold and the radiator. Remove the air conditioning compressor drivebelt and upper idler pulley bracket. Unbolt the coolant tube from the front of the engine. Loosen the hose clamp and detach the lower radiator hose from the thermostat housing cover. Remove the thermostat housing cover from the engine. Remove the drivebelts and the water pump drain plug from the front of the engine. Detach the lower radiator hose and coolant by-pass hose from the thermostat housing cover. Remove the intake manifold from the engine. Detach the hose from the water outlet housing and remove the water outlet cover from the engine. Clean off any old gasket or sealant on the thermostat housing and thermostat cover using lacquer thinner. Apply a bead of RTV sealant around the perimeter of the thermostat cover. Install the new thermostat with the jiggle valve facing upward and bolt the cover in place within 5 minutes of applying the sealant. Wait at least half an hour for the sealant to cure. Refill and bleed the cooling system. Run the engine and check for leaks and proper operation.

Before attributing cooling system issues to the thermostat, it's important to check several factors. Verify the coolant level, assess drivebelt tension, and ensure the temperature gauge (or light) is functioning properly.

If the engine takes a long time to warm up, it's likely that the thermostat is stuck open. In this case, the thermostat should be replaced.

If the thermostat doesn't open and close as specified, or sticks in any position, it should be replaced.