The only way to repair the thermostat on a Nissan Xterra is to replace it. The thermostat has no parts that can be fixed or replaced. Heating and cooling weakens the moving parts on the unit. Any attempt at repair is generally futile and results in replacement in a short time. A thermostat is inexpensive to buy, but replacing it is complicated because there are several steps necessary to access the thermostat. When the car overheats quickly or does not warm up properly, the thermostat is the likely culprit.
Raise the hood and let the car cool. Open the radiator cap to release any leftover pressure. Place a large container under the radiator and open the drain on the bottom of the radiator with your fingers or a pair of pliers to drain the coolant. If you do not perform this orderly draining of the coolant, it will pour out all over the place when you open the thermostat housing. Doing it this way allows you to capture the coolant and reuse it at the end of the job.
Use a wrench and remove the bolts that hold the cooling fan in place and lift the fan up and out of the vehicle. You may need to remove a housing before you can access the fan depending on the year of the Xterra that you are working on. Place a wrench on the drive belt tensioner and rotate it counterclockwise to loosen the belt so it can be removed. Once the belt is out of the way, you should be able to reach the thermostat housing.
Loosen the clamp holding the lower radiator hose to the thermostat housing with a wrench and slip the clamp up the hose and out of the way. Pull the hose loose from the thermostat housing. With a wrench, remove the bolts that hold the housing in place and lift it off of the thermostat. Make a note of how the thermostat is positioned in its mount. The new thermostat will need to be placed in exactly the same way.
Pull the thermostat out of the mounting. Use a scraper and remove any old glue or gasket pieces from the mounting and housing. Apply a small amount of gasket sealer to the mounting and press the new gasket against the sealer to hold the gasket in place during the rest of the installation. Cover the gasket with a thin layer of gasket sealer.
Slide the new thermostat in place in the mounting. Replace the housing and install the bolts back into their respective holes by tightening them with the wrench. Slide the radiator hose back onto the housing. Push the clamp down on the hose until it is on the neck of the housing. Tighten the screw on the clamp until the hose is secure.
Place the wrench on the belt tensioner and rotate it counterclockwise so that the drive belt can be reinstalled. Put the cooling fan in position and insert and tighten the bolts. Replace the housing if it had to be removed. Make sure the drain valve on the radiator is shut.
Add the coolant back into the radiator and add any additional coolant that may be needed to fill the radiator. Replace the radiator cap onto the radiator. When about 45 minutes has passed since the thermostat housing was tightened down, start the car. Check for leaks before driving the car.
