Change thermostat - 2004 Chevrolet TrailBlazer

Typically, the thermostat is located under an aluminum fitting where the top radiator hose meets with the engine block or the intake manifold. You need to drain the antifreeze into a container from a valve at the bottom of the radiator so that the level is below the top of the engine block. Save this for reuse or disposal. Then loosen the hose clamp and remove the top hose from where it meets the engine block or manifold. Now, loosen the two or three bolts that hold the aluminum fitting from the engine block or manifold and remove it, revealing the thermostat.

Pay attention to the orientation of the thermostat. Now, clean up the mating surfaces of the fitting and the manifold. Reinstall using a new thermostat orientated the right way, a new gasket and/or silicone sealer, and then the fitting. Attach the hose, refill the radiator, and test for leaks.