How to Install a Miata Thermostat

By Al Coreli -

(Also see this article)

The installation is easy. (forgive me if you know some of this). Begin with the engine cold.

  1. Follow the upper radiator hose from the top of the radiator to where it attaches to the front of the engine. This is the thermostat housing.
  2. Remove the two bolts (1.6) or bolt and nut (1.8?). You do not have to disconnect the radiator hose.
  3. Tap up from under the neck of the housing lightly to disengage the old thermostat gasket. Remove the housing. You will see the thermostat directly. You will also note that nasty green fluid will pour out from between the mating surfaces, this is cool. If the antifreeze has been in there more than two years, it is probably time to replace it also. While everything is apart, it is very easy to flush the engine and radiator. Please do not let that green slime antifreeze release itself into the environment. It tastes very sweet and will poison and kill (very violently) anything that consumes enough of it. For years we used to "taste" the fluid to see how concentrated it was. A chemistry professor told me the substance NEVER leaves your body. It just builds up till there's enough to kill you, then it does. Be Careful.
  4. LOOK and SEE which way the thermostat is mounted in the engine. The new one must go in the same way. Remove the old thermostat and launch over your left shoulder. Loudly proclaim that you are the planet's greatest Miata mechanic, evoking absolute confidence in yourself. Open 1 (one) bottle of your favorite malt and hops beverage, and consume exactly one half of its contents in one big gulp. This will prepare you for step 5.
  5. Procure one DULL single edge razor blade. Take said blade and proceed to scrape off the old gasket from both the thermostat housing and the engine. DO NOT gouge the aluminum, or you will have a leak! This is a time honored practice, this "gasket scraping". Be sure to clean out the recess for the thermostat. Do not let any pieces of old gasket fall down into the engine. All of our great mechanic forefathers started by learning how to scrape gaskets correctly. (If you lived closer, you could swing by here, and I would provide beer and scrape the gasket for you....I love to scrape gaskets!) When you are done with the ceremonial scraping, raise the aforementioned refreshment bottle and empty its bounty into your digestive tract.

    NOTE: The next step deals with very complicated mechanical processes, and I want you to be aware that there are many different methods to complete many automotive processes. I would hate for someone to tell you what I said was wrong when it isn't. There are many ways to seal a gasket. I myself use numerous ways, depending on the condition of the materials being sealed. Since we were blessed with peel and stick gaskets, we can dispense with the other time honored practice of smearing gorilla snot lightly over the housing side of the gasket. All we have to do is Peel-N-Stick our gaskets to the thermostat housing. By now you are a true pro. Go to the fridge/snowbank (It is Canada, right ) and grab another bottle of liquid WrenchMeister, find the opener (a screwdriver will do), and down that sucker.


  6. Drop the new thermostat into the recess where the old one came out. Be sure to orient the new 'stat the same way as the old one. Git yerself some o'dat fine sealant material, blue silicone. Put a very light coating of this on the gasket that is attached to the housing. Do not let the silicone get so thick that it is opaque. Spread it with your finger about as thick as a sheet of very thin paper, that's it. Place the housing over the top of the 'stat. Then insert the bolts (nut), and torque them down EVENLY. Do not worry about undertightening, just make them snug, and if it leaks later, you can always make them a LITTLE tighter. We don't want to strip or crack anything. If you prepared the surfaces correctly, there should be no problem sealing.
  7. Fill the system from the radiator cap opening. The procedure for opening the rad' cap is as follows: Turn one quarter turn counter-clockwise. Push down on the cap and continue turning counter-clockwise till the cap stops. Lift the cap off and fill the system with your favorite antifreeze mixture. Mine's 60/40 Prestone/water. Start the car, let it warm up. If you are watching the level through the filler neck, you will notice that when the engine reaches operating temperature, the level in the rad' will fall and the contents will appear very hot. This is the time to fill the system with more coolant. Wait a few minutes (I wait for the fan to come on) and fill the radiator all the way up and install the cap. If you have any remaining coolant, put it in the overflow bottle if it needs it.

Relax, have fun. At least it's not a British car that you HAVE to work on.