The thermostat on the Nissan 350Z is an important component of the engine cooling system. It governs the flow of coolant to the engine to maintain optimal engine temperature. When the thermostat fails, it can fail in the open position (in which case the engine will not warm up properly), or in the closed position (in which case, the engine will overheat).
Park the Nissan 350Z on level ground and turn the engine off. Wait for the engine to completely cool.
Raise the hood and check the radiator cap to see if it is hot. If not, remove the cap from the radiator.
Slide the coolant catch pan under the driver side of the radiator. Unplug the coolant temperature sensor wire on the bottom of the radiator.
Remove the coolant temperature sensor itself from the bottom of the radiator with the adjustable wrench. Turn the sensor counterclockwise to remove it. Be careful not to bend or damage the electrical connector tabs. Let the coolant drain into the catch pan. Then put the sensor back into the bottom of the radiator and tighten it with the adjustable wrench. Plug the sensor wire back in.
Go back to the top of the engine and locate the top radiator hose. The top radiator hose is attached to the radiator on one end and the thermostat housing on the other end. Remove the hose clamp from the radiator hose at the thermostat housing with the flat head screwdriver.
Slide the hose clamp back on the hose about six to eight inches. Then, slide the top radiator hose off of the thermostat housing inlet port.
Remove the three bolts that are holding the top half of the thermostat housing onto the engine, using the ratchet wrench and socket.
Pull the top half of the thermostat housing off of the top of the engine block. Slide the thermostat out of the top of the engine block, noting its orientation. Scrape any old gasket material off of both mating surfaces, using a gasket scraper or flat-head screwdriver. Be sure that both surfaces are clean. Put the new thermostat in the same way the old one came out.
Apply a very small amount of the red high temperature silicone to the bottom of the thermostat housing. Then, match the three holes on the new gasket with the three holes on the bottom of the thermostat and press the new gasket onto the bottom of the thermostat housing. The red high temperature silicone will hold the new gasket in place.
Slide the top half of the thermostat housing back into place. Put the three bolts back in place and tighten the bolts down with the ratchet wrench.
Slide the top radiator hose back onto the inlet port of the thermostat housing. Slide the hose clamp back over the hose and the inlet port of the thermostat housing. Tighten the hose clamp down tight with the flat-head screwdriver.
Fill the radiator back up with antifreeze coolant until the radiator is full.
Start the engine and let it idle. As it warms up (this will take a few minutes) the thermostat will open and the coolant level in the radiator will drop. Keep adding more coolant to the radiator until the coolant level stabilizes at the top of the radiator. Put the radiator cap back on and continue to let the engine idle for another 10 to 15 minutes.
Turn the engine off and inspect the thermostat housing, coolant temperature sensor and the top radiator hose for leaks. Close the hood. After driving the car, check the coolant reservoir level--it may drop as air continues to work its way out of the system.
