Tips for changing a thermostat on your car:

This is a for typical installation, if you have any concerns, consult a professional mechanic and / or a service manual for your car.

Things to have ready:

New thermostat correctly rated for your car. Check owners manual or auto parts store for correct size and rating. (Thermostats DO vary in quality. A few dollars extra now may save you from doing this again later.)

Something to remove old gasket material such as flexible putty knife and / or wire brush.

Sealer such as Ultra Black Silicone Gasket, Ultra Blue, Permatex Avaiation or equivalent.

New anti-freeze if it has been over a year or two since it was changed.

Water to mix with anti-freeze -- some auto manufacturers recommend distilled or de-mineralized.

Tools - socket wrench and sockets, screwdrivers.

Paper & pencil - to make a sketch as you remove the old thermostat.

Paper towels or cloth.

Fresh water supply - to rinse off spilled anti-freeze.

NOTE: Never open the radiator cap while the engine is hot. Coolant under pressure may spray and cause burns, and the radiator cap may hit you in the head. Before starting, allow the engine to cool.

Locating the Thermostat: If you follow the upper radiator hose back to the engine, it often connects to the housing for the thermostat. Click here for sketch of thermostat & housing    If you are not experienced in car repair, this is a good point to decide if you want to try this yourself.  You will need to be able to get access to the opening where the thermostat is located to get at the bolts and remove any left over gasket material from the existing installation.  You might also want to invest in a factory service manual, or a after - market manual for your car available at many auto parts dealers.

First, drain the level of the coolant below the level of the thermostat, or completely if you are changing the coolant. There is usually a drain plug on the bottom of the radiator, or a valve on the lower back side. Many of the valves turn in to open, opposite of what some might expect. You may find it easier to work by also removing the upper radiator hose from the housing.

Next remove the bolts holding the thermostat housing. Usually there are two - loosen the first one only slightly, then the same to the other, until both are loose. This will reduce the imbalance of force on one side compared to the other, and reduce chances of cracking the housing. Do this in a similar manner when re-installing the bolts. As you remove the housing, pay attention to the direction of the thermostat. Clean the housing and engine opening of any old gasket material. Have a cloth or paper towel handy to clean up any pieces of the gasket that fall into the engine opening.

Usually either the engine or the housing has a small grove in it to hold the thermostat in place. You will place the thermostat there.  Some manuals recommend adding sealer to the thermostat gasket for the best seal. Recommendations vary as to silicone (use sensor safe rated for newer cars) or as in a tip from the author of  The Drive Train Page, aviation grade Permatex.  Install the gasket over the thermostat and housing, and place back on the car in reverse order. (A tip from a local radiator shop: They often find excess silicone gasket sealer (or RTV) in the cooling system from folks who have used a lot in sealing the thermostat. - It doesn't take a lot to make a seal)  Be careful not to over-tighten the bolts, you can crack the housing or the engine mount. The best way to re-tighten is with use of a torque wrench. You can now re-connect the hose and refill the radiator. (Remember to close the drain)

Normally auto manufacturers recommend a 50% - 50% mix of anti-freeze and water. Do not exceed about 70% antifreeze, the freezing point actually comes up from there. After your first refill, you may need to add more after the engine cools down. The thermostat will trap air, and you will probably need to re-fill again after the new thermostat opens once the engine reaches the operating temperature, and allows air to escape.

If you drian your radiator, chances are some coolant is left in the engine and heater core. To do a simple flush, fill the system with water and run the car until the thermostat opens. (The upper radiator hose will become hot.)  Shut off the car and drain the system. (Remember to close the drain when finished).  A Flush and Fill T kit (Prestone and some others make them) also are very good to flush the system. Now, since there is probably water left that will not all drain out, to make your 50% - 50% mix. you will have add enough anti-freeze to make a 50% mix, then fill the rest with water. Run the engine agian till the thermostat opens. After the engine cools down, re-check the coolant level and add as needed. It is a good idea to check again in a day or two, as any trapped air that is purged out may cause the coolant level to drop.

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