This how-to shows you how to replace your thermostat. Your thermostat could be the cause of an overheating problem (stuck closed), or a problem where your engine does not reach operating temperature (stuck open). You may also need to replace your thermostat with a lower than stock temp unit if you are installing certain performance chips. The stock thermostat opens at 195°. There is no performance gain to be seen by switching to a lower temp (180° or 160°) thermostat unless a certain modification requires it. All this is really going to accomplish is giving you colder heat in the winter. I just replaced mine with a stock unit.

Remove the fill cap from the coolant overflow to alleviate any pressure in the system.

Remove the intake hose to give you a little more room to work. Wrap some rags around the base of the thermostat housing to absorb any coolant loss. If you do this on a cold engine, coolant loss should be minimal, so you don't need to worry about draining the system.

Next, remove the vent pipe from the thermostat housing using a 1/2" box wrench. Once it is loose, move it out of the way.

Remove the 13mm bolts holding the thermostat housing down. A standard 13mm socket with extension will work for the left side bolt, but the right side has a nut on a stud, so you will need a deep socket to clear the stud to remove it. If you wish, you can use the deep socket for the left bolt, and not have to worry about using an extension. The extension just gives you a little better clearance to swing the ratchet.

Once the bolts are out, slide the housing off to the side to expose the thermostat. You may lose a little coolant out of the hose at this point, but it should be minimal.

Remove the thermostat. You may lose some more coolant now, but as long as you have your rags in place, they should be able to absorb all that is lost. If you wish to check the old thermostat to see if it was stuck closed, throw it in a pot of boiling water and see if it opens up.

If the rubber gasket stayed in the block, and your new thermostat already has a gasket installed, remove the old gasket from the block using your fingers or with the tip of a screwdriver.

Install the new thermostat. Be sure you don't install it upside down ;)

Reassemble everything that you took apart. Top off the overflow tank with the proper coolant/water mixture (typically 70/30).

Start the car and check for leaks. Go take her for a spin and be sure the car is operating in the proper temperature range.