Thermostat replacement is generally done if a car is overheating. The other possibility is that the car is no longer heating up correctly due to the thermostat sticking. Before changing the thermostat verify that the engine coolant is full and that the cooling fan is working when the car is up to temperature. You will also need to find out the recommended temperature of your car’s thermostat when you purchase it. This sunbird has a 3.1 liter v6 engine that will randomly overheat. Another possibility is that the water pump is bad. Removing the radiator cap (if possible) when it is cool, can some times be helpful to see if flow is occurring although it won’t always work.
Here is the location of the thermostat housing which contains the thermostat below it. You will need to remove anything in the way of the thermostat housing for it to clear. The air tube shown will be swung out of the way
Next this coolant line in the yellow circle will need to be removed, then the two bolts shown by the two red arrows. The right side has a nut holding a tab, under it will be the bolt. You wont need to remove the radiator hose on this one instead just lift the thermostat housing up.
Here is the thermostat sitting in the hole. Pay attention to the direction that the thermostat faces so that you put the new one in the right way.
Here is the new thermostat. You can see that the “gasket” is actually a rubber seal (red arrow) that is being slipped on it in this picture. Some housings are different and require a paper gasket to seal it down. If this is the case you will need to carefully scrape the gasket off the housing and where it bolts to on the engine. Use a razor blade scraper to do this but be careful to not damage the housing or engine with nicks. Use brake cleaner or alcohol to clean the surface after the old gasket is gone. Apply a light film of silicone or rtv sealant to both surfaces of the thermostat gasket before applying. At this point you can place the thermostat back in and reverse the previous process and you should be done.