A car thermostat sits on a table.

Tips On How to Change a Car Thermostat

Your car thermostat plays an important role in keeping your engine cool and safe and running dependably. It also has a tendency to wear out over time and need replacement. Luckily, changing a thermostat isn’t usually a tough job, as long as you keep a few things in mind and are willing to set aside the time for it.

Get Set Up

The thermostat is a temperature-controlled gatekeeper that allows the flow of coolant through the engine and radiator. On a cold start, it remains closed to help the engine reach operating temperature. When it heats up, it opens and allows coolant to flow. Thermostats fail by becoming stuck open or closed — the latter leads to more dire consequences. If you’ve managed to diagnose the thermostat failure as one or the other, get some tools and parts together: You’ll need a drain pan, tools, new coolant, a new thermostat, a new thermostat gasket and a little silicone sealer.

Take It OutHow To Change a Thermostat

First, don’t work on the cooling system of an engine that’s still hot. Check out the owner’s manual and the situation under the hood before you begin. When the engine is cool, locate the thermostat housing. Drain the radiator and remove the hose at that connection (this is a good time to the the condition of your hoses). Be careful to prevent debris from falling inside.

Next, grab your tools and remove the thermostat housing. Depending on your vehicle, there might be other components you have to remove to get to it.  Once the housing is removed, the thermostat should be exposed. Note that you might have to pry it out with a flathead screwdriver.

Switch It Over

Feel free to test your thermostat at this point, but honestly if you’ve come this far, you might as well change it. Scrape off any residual residue around the housing and block. Don’t get too aggressive with the scraper, as aluminum is a popular metal for housings and you can gouge the sealing surface. Double-check that the new thermostat has the proper temperature rating, and acquaint yourself with the direction of flow, because it’s very easy to install it backward and have to do this all again. Use a little silicone sealer (RTV) to hold the thermostat to the housing, install the gasket on the block and match up the two surfaces, making sure nothing slips out of place.

Put It Back

Next, tighten each of the housing bolts a little at a time for even pressure, making sure they all end up tight. A good torque wrench and a service manual are your friend in making sure the bolts are properly tightened. Too loose and it might leak, too tight and you can actually crack the thermostat housing. Reconnect the hose and any other components you had to remove. Add coolant, making sure you’ve tightened the radiator drain plug, then install the radiator cap. At this point, you should be good to fire up the vehicle and check for any leaks. Let it run for a while under observation. Continue checking for leaks, watch the gauges on the dash and look out for any warning lights. If the thermostat opened at operating temperature after a few minutes (or a bit longer in the winter), then your job is done!

Of course, if you’re not comfortable doing this yourself, take your vehicle to the experts at your local NAPA AutoCare. Problems with the engine cooling system are not something to play around with.

Check out all the heating & cooling systems parts available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more tips on how to change a car thermostat, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photos courtesy of Blair Lampe.

about author

Blair Lampe

Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter.  In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.

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