Car Thermostat Replacement - 10 Important Tips

Updated on March 20, 2016

Car thermostat replacement is not difficult. You don't need special skills or special tools. In fact, you just drain some coolant, disconnect a hose, a housing shell, and install a new thermostat. Then put everything back together.

But it's what you don't know what will get you in trouble.

Overlooking a small detail that seems inconsequential can lead to cooling system problems and more expensive repairs.

These 10 essential tips will help you replace your car thermostat properly. They'll help you avoid issues like coolant leaks, thermostat housing damage and stripped threads associated with poor thermostat service.

You'll find most car thermostats near the top and to one side of the engine — which makes your job easier — and less frequently toward the lower section of the block. And, while you may need to remove one or two accessories to gain access to the thermostat, you can replace it in your own garage in about an hour or so, using a few simple tools.

If you know your car thermostat has failed go ahead and read this tips before you replace it. However, if you don't know whether the thermostat is bad, check this other article about troubleshooting the thermostat.

* Catch pan
* Floor jack, if necessary
* 2 jack stands, if necesary
* Ratchet and socket set
* Standard and/or Phillips screwdriver
* Rags
* Plastic scraper
* Fresh coolant, if necessary
A stuck thermostat can overheat and seriously damage your car engine.
A stuck thermostat can overheat and seriously damage your car engine. | Source

Car Thermostat Replacement

The best way to go about your repair job — if this is the first time you are going to replace a car thermostat — is to use the service manual for your particular vehicle make and model. The manual provides a step by step procedure to replace the thermostat plus torque specifications. Buy an inexpensive, aftermarket copy online or through one of your local auto parts store. I highly recommend you get a copy since most likely you'll need to remove air from the cooling system — "burp" the system — after you finish your repair job.

Following your service manual, pay attention to the next important tips to avoid potential repair problems associated with car thermostat replacement.

So, when replacing the thermostat . . .

1. Wait for the radiator and engine to cool before attempting to replace the thermostat. When hot, the cooling system is under pressure and you'll seriously burn yourself unintentionally by releasing a gush of hot or boiling coolant.

2. Drain about two quarts of coolant using the radiator drain valve before disconnecting the upper radiator hose from the thermostat shell to bring the coolant level to below the thermostat housing. This will prevent coolant from splashing over belts and other components after separating the upper radiator hose. Coolant will cause some parts, specially rubber, to deteriorate over time. You may need to raise the front of your vehicle and remove a splash shield to reach the radiator valve. After raising your vehicle, block the rear wheels with a couple of wheel chocks and support your car on jack stands.

3. Disconnect the upper radiator hose from the thermostat housing. To locate the thermostat housing, just follow the upper radiator hose back to the engine. On some models, you need to remove the air filter assembly to clear the area around the thermostat case and, if equipped, disconnect the thin hose and electrical sensor connector from the thermostat housing. After removing the clamp securing the upper hose to the thermostat casing, you may find out that the hose refuses to come off. To break the seal, carefully insert a thin, flat-head screwdriver at different points between the hose and the fitting. Then, twist the hose back and forth while carefully pulling it off the thermostat housing.

4. Use a six-point wrench or socket of the correct size when removing the two or three housing mounting bolts. Using a six-point tool will prevent rounding off the bolts' heads.

5. When trying to lift the thermostat housing you notice it doesn't move, lightly tap it with a rubber mallet or screwdriver's plastic handle. Do not use a wrench or a regular hammer.
Thermostat casings are made of aluminum or plastic and can easily brake.

6. Carefully lift the thermostat housing from the engine and, before removing the thermostat, pay attention to the way the thermostat aligns inside of the housing. To check the alignment, note in which direction the bleed pin — near the edge on the round base of the thermostat — points to. You will have to install the new thermostat with the bleed pin pointing in the same direction as the old one. Some thermostats come with a guiding tab that fits into a recess on the mounting base to prevent misaligning the thermostat.

7. After removing the thermostat, cover the thermostat opening on the engine with a clean rag to prevent sealant or gasket material from going into the engine. Then, clean the thermostat housing and engine mating surfaces using a plastic scraper, if you need to remove old gasket material and sealing compound. Avoid using a metal scraper that can gouge the mating surfaces. It'll lead to coolant leaks. Some thermostats come with a rubber O-ring instead of a traditional gasket. Before installing it, apply a light coat of fresh coolant to the O-ring.


8. When buying the new thermostat, get one with the same temperature range your car manufacturer specifies for your vehicle. You'll find this information in your vehicle service manual. If you do not have the manual, check one on the reference section of your public library or call your local dealer’s parts department. If you install a thermostat with a different range temperature, you'll end up with all kinds of performance problems because your engine will operate out of its normal temperature range.

9. Most new thermostats come with their own gaskets, but not all. So check that your new thermostat includes one or buy one. Remember that you may need to apply sealant to the new gasket — check your vehicle service manual. Only use the sealant recommended by your car manufacturer and use a small amount. Using too much sealant will damage an oxygen sensor and disrupt engine performance.

10. Compare the new thermostat to the old one. Then, position the new one in place, and tighten the housing bolts using a torque wrench. Your car repair manual specifies the torque value for the thermostat mounting screws. This prevents cracking a plastic shell, leaving the shell loose and causing coolant leaks, or damaging the bolts' threads. When ready, top up the radiator with coolant to replace the amount you removed, and bleed the cooling system, if your car manufacturer recommends it — check your vehicle service manual. Trapped air will cause your engine to overheat. Watch the next video to get an idea about how to bleed your cooling system. Then, test your repair job by starting the engine and checking for coolant leaks and coolant level.

A car thermostat replacement job is within the reach of the average car owner. You don't need special skills or tools. And you can do it in your own garage. But it doesn't mean that nothing could go wrong. The little details will get you in trouble when you don't know or forget about them. Doing a hit-or-miss repair job or following the wrong procedure will result in a much more expensive job than taking your car to the repair shop in the first place. If in doubt, consult the vehicle repair manual for your particular car make and model. The ten tips described here point out the most common details you are most likely to miss and get you in trouble when replacing your car thermostat. So keep these tips handy and consult them as necessary.


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    • Dan Ferrell profile image

      Dan Ferrell 2 months ago

      Hi John,

      remove the thermostat and flash the system. When you're ready to refill, install the new unit and purge the system.

      Good luck.

    • profile image

      john 3 months ago

      I need to replace my thermostat and I need to flush out my cooling system. Should I remove the old thermostat first or do my flush when I put in the new thermostat?

    • Dan Ferrell profile image

      Dan Ferrell 5 months ago

      Hi JP,

      380 Euros (425 US dllrs) seems a little bit on the high end. Call other shops and see if you can get a lower price between 110 - 254 Euros (130-300 US dllrs). Labor is expensive.

      Good Luck

    • profile image

      JamesPrim 5 months ago

      I took my car (a 2009 Ford Fiesta) to a garage as the coolant fluid was leaking from somewhere. They told me the thermostat needed replacing and quoted 380 Euros (I live in Madrid) all in for the replacement.

      Does that seem reasonable? I don´t know anything about cars to be honest so prefer to have it done by a garage but obviously I don´t want to be ripped off.


    • Dan Ferrell profile image

      Dan Ferrell 6 months ago

      Hi Rob,

      The piece may get stuck in one of the water packets or reach the water pump and cause wired stuff, depending on the size of the piece. Maybe the part didn't go to fat deep into the hole. Try to use one of those flexible magnetic pickup tools. Harbor Freight has some cheap ones that come in handy for this tasks.

      Good luck.

    • profile image

      Rob 7 months ago

      Oops, I broke the thermostat when removing it and a piece fell into the hole. Am I screwed?

    • Dan Ferrell profile image

      Dan Ferrell 9 months ago

      Hi Greg,

      It doesn't seem likely, unless your model gets a different one for the thermostat itself. Check both and see which one fits best, you may have one for a different model.

      Good luck

    • profile image

      Greg 9 months ago

      AR there two black gaskets for the 2010 silverado.they gave me two