The thermostat in an Xterra controls the flow and temperature of your engine coolant. If your SUV takes a long time to warm up, or if it overheats frequently---monitor the temperature gauge in your dashboard closely---your thermostat may be in need of a replacement.
Disconnect the battery.
Remove the lower engine cover and drain the coolant from the radiator.
Remove the engine cooling fan.
Take out the air cleaner and disconnect the air intake duct if you have a four-cylinder Xterra. You may also need to remove the power steering bracket.
Remove the upper radiator hose, if you have a six-cylinder Xterra. Remove the air conditioning belt and the pulley bracket for the idler and detach the lower radiator hose from thermostat's housing unit.
Remove the cover to the thermostat housing unit. Some fluid may spill as the seal is broken.
Remove the thermostat.
Clean off the housing unit by using paint thinner to clean the edges where old gasket residue may remain. Once clean and somewhat dry, apply sealant around the edges of the unit.
Install new thermostat with the valve in the "up" position. Be certain to do so quickly, before the new sealant dries.
Replace the housing unit cover and repeat the installation steps in reverse order; the final step is refilling your radiator with coolant/antifreeze.
Wait at least 30 minutes for the sealant to dry before starting the engine, to avoid possible leaks. Once the engine is started, check for leaks as well as the engine's temperature on the appropriate gauge.
