How to Replace a Car Thermostat (In 15 Easy Steps)

Thermostats are one of those auto parts that is fairly inexpensive and straightforward to replace yourself. Although the part is inexpensive, the labor rate at a mechanic can drive up the cost of replacement.

It’s always a good idea to search online for a how-to guide for your exact vehicle. If you can get your hands on a factory service manual or a third party repair manual, that’s even better.

Here are some general steps you will need to follow to replace a thermostat on your own vehicle. 

Steps to Replace a Thermostat

These steps are common to nearly every vehicle you will need to replace a thermostat on, and should give you an idea of what is involved with the repair process.

1) Gather Your Tools

Gather your tools: clean drip pan, rags, new thermostat, new thermostat housing gasket, pliers, ratchet set, safety gear (goggles, gloves), torque wrench, torque specs for your vehicle, plastic scraper, funnel.

2) Cool Engine

Make sure your car is cool (hasn’t run recently) and is in a clear work space. You’ll generally want to let the car cool down for at least 3 hours before you work on the cooling system.

3) Open Cooling System

radiator cap

Open the radiator cap and set it somewhere safe. If you see any leaks around the cap, replace the radiator cap as well.

See Also: 7 Components of a Cooling System

4) Grab a Drip Pan

Place a drip pan underneath the radiator drain plug under the car. If you plan to reuse the coolant, make sure your drip pan is clean. 

5) Drain Coolant

Turn the drain plug so that the antifreeze/coolant runs into the drip pan. You will need to let enough out so that the thermostat is exposed – usually about half. Some people take this opportunity to replace the coolant if the coolant is brown, or it’s been a long time since it was replaced.

Be very careful to leave the coolant somewhere that animals and children can’t access it. Antifreeze is sweet smelling but very toxic to people and animals. 

6) Loosen Thermostat Housing

Use a ratchet to loosen the bolts that attach the housing of the thermostat to the engine. The radiator hose may need to be removed if it’s in the way of removing the thermostat.

The gasket should come off as well. Many manufacturers call for the thermostat housing gasket to be replaced along with the thermostat.

7) Remove Thermostat

bad thermostat

Check the engine where the thermostat housing was just removed to find the thermostat itself. It should look like a cylinder with a metal ring and a valve attached at the top.

You should be able to remove the thermostat by hand. If it’s stuck, you could grab a pair of pliers for a bit more leverage.

If you don’t see the thermostat, check the thermostat housing; sometimes the thermostat gets stuck in the housing. Save the old thermostat until you finish the job, in case you encounter any issues (such as buying the wrong part).

If you don’t know which new thermostat to buy, check the ring of the old thermostat. There may be some numbers on there, like a part number or the temperature rating, which should help you figure out what to buy.

If all else fails, you could call your local auto parts store and they could help you find the correct replacement part.

8) Remove Gasket Residue

Use a plastic scraper to scrape off any remaining gasket residue from the flanges of the housing and the engine where the housing attaches. If the mating surface is not smooth, there may be leaks later on.

Be careful when scraping, as the parts may be made of softer metals such as aluminum that could be damaged. 

9) Install New Thermostat

replacing car thermostat

Place the new thermostat in the engine port in the same orientation as the old one – spring side down, valve side up. This makes sure that it works correctly and minimizes leaks. 

10) Install New Gasket on Thermostat Housing

Place the new gasket on the thermostat housing flange, being careful not to cover any holes.

Some vehicles actually have a gasket that goes on the thermostat before it’s installed, which is why it’s important to look up your exact vehicle before doing this job. 

11) Reinstall Thermostat Housing

Replace the housing by lining up the bolts and hand-tightening first then using a torque wrench to tighten them to the manufacturer’s specifications. Too loose could result in leaks or a blown hose, and too tight could damage the aluminum housing or strip the threads in the engine block. 

If you do strip the threads in the engine block, it is usually fairly straightforward to repair the damaged threads using a thread repair kit like a Helicoil or Timesert.

Make sure you buy the correct thread size when you buy your thread repair kit.

12) Refill Coolant

Refill the coolant by pouring it from the drip pan directly into the radiator or into the coolant reservoir. A funnel will minimize the chance of spilling coolant all over the engine bay.

13) Burp the Radiator and Replace the Radiator Cap

Burp the cooling system by removing the cap at the highest point of the cooling system. This is often the radiator cap, but some vehicles have a separate cap for this. Let the engine come up to operating temperature.

Wait for the thermostat to open. This can take 5-15 minutes. During this process, you should see air bubbles coming from the cooling system.

After the bubbles disappear, turn off the engine and replace the radiator cap, sealing the cooling system. 

As you run the engine, coolant in the engine will expand. This will spill coolant onto the ground if you don’t have a funnel that seals against the radiator.

If you don’t have one of these funnels, leave the drip pan in place while burping the cooling system. 

14) Watch Temperature Gauge

For the next few drives, keep a very close eye on the temperature gauge. The gauge should stay near the middle, as it would when the vehicle is running at operating temperature.

If the temperature starts to spike toward the hot side, turn off the vehicle. Verify that you don’t have any air pockets in the cooling system. Make sure the thermostat was installed in the correct orientation.

Sometimes there is a little hole in the thermostat that needs to be positioned in a certain orientation to allow air bubbles to escape. 

15) Check Coolant Level

It is not uncommon for a little bit of air to be trapped in the cooling system, even after burping the system. This air should work itself out over the next few drives.

Check the coolant level periodically for at least the next month or so. Add coolant to the overflow reservoir until the level is between the min and max lines.


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