Car Thermostat Replacement: 10 Important Tips

Updated on January 26, 2019
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

A bad thermostat can cause engine overheating or not allowed the engine to reach operating temperature.
A bad thermostat can cause engine overheating or not allowed the engine to reach operating temperature. | Source

Car thermostat replacement is not difficult. But, you do need to pay special attention to key points in the process.

What to Know to for Car Thermostat Replacement

  • How to access the thermostat housing
  • Using the right tools
  • Preparing the surfaces for the new installation
  • Getting the correct thermostat for your application
  • Installing the new thermostat correctly
  • Bleeding the cooling system to prevent overheating

Overlooking a small detail that may seem inconsequential at first can lead to cooling system problems and more expensive repairs.

The 10 essential tips presented in this guide 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 change it using these tips. However, if you don't know whether the thermostat is bad, check this other article about troubleshooting the thermostat.

Some Tools You May Need
Car Thermostat Replacement
1. Cool the Engine
2. Drain Some Coolant
3. Access to the Thermostat Housing
4. Use the Appropriate Tool
5. Remove the Thermostat Housing
6. Check Thermostat Alignment
7. Clean the Mating Surfaces
8. Get a New Thermostat
9. Use the Appropriate Seal
10. Install the New Thermostat
A Systematic Approach to Car Thermostat Replacement


Always work on a cool engine when replacing the car thermostat to prevent serious skin burns.

Some Tools You May Need
* Catch pan
* Floor jack, if necessary
* 2 jack stands, if necesary
* Ratchet and six-point socket set
* Standard and/or Phillips screwdriver
* Rags
* Plastic scraper
* Fresh coolant, if necessary
* Chocks
* Six-point wrench set
* Torque wrench
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 your first time replacing a car thermostat—is to use the service manual for your particular vehicle make and model.

However, the next ten tips may be sufficient to replace the thermostat in many models, since the unit is readily accessible, and you may not need to remove components, except some parts from the air cleaner assembly.

If you still need some help, though, the manual provides a step by step procedure to replace the thermostat for your specific model, how to deal with components that might block access to the thermostat housing, torque specifications, and the bleeding process for your vehicle, if necessary.

Buy an inexpensive, aftermarket copy online like this Haynes manual, from Amazon. It comes with many step-by-step procedures for many maintenance, troubleshooting, and replacement tasks that will help you in the future. So the manual pays for itself in a few days.

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

So, let's start replacing the thermostat.

Make sure the engine is cool before you start replacing the thermostat.
Make sure the engine is cool before you start replacing the thermostat. | Source

1. Cool the Engine

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 Some Coolant

Drain about two quarts of coolant using the radiator drain valve before disconnecting the upper radiator hose from the thermostat shell. This will bring the coolant level to below the thermostat housing and prevent coolant from splashing over belts and other components after separating the upper radiator hose.

  • Coolant causes 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, chock the rear wheels and support your car on jack stands.

3. Access the Thermostat Housing

Disconnect the upper radiator hose from the thermostat housing. To locate the thermostat housing:

  • 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. If necessary, 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.

Use a line wrench or six-point socket tool to prevent damage to bolts.
Use a line wrench or six-point socket tool to prevent damage to bolts. | Source

4. Use the Appropriate Tool

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

5. Remove the Thermostat Housing

When trying to lift the thermostat housing, if 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 break.

6. Check Thermostat Alignment

Carefully lift the thermostat housing away from the engine. Before removing the thermostat, pay attention to the way the thermostat aligns inside the housing.

  • To check the alignment, note 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 maligning the thermostat.

7. Clean the Mating Surfaces

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.

To clean the thermostat housing and engine mating surfaces:

  • Use 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. This may lead to coolant leaks.

Make sure the new thermostat aligns perfectly inside before tightening the mounting bolts.
Make sure the new thermostat aligns perfectly inside before tightening the mounting bolts. | Source

8. Get a New Thermostat

When buying the new thermostat, get one with the same temperature rating your car manufacturer specifies for your vehicle. You'll find this information in your vehicle service manual.

  • Most vehicle models use a 192F or 195F rated thermostat.

  • If you install a thermostat with a different rating temperature, you'll end up with all kinds of performance problems like fuel, emission and ignition system problems, because your engine will operate out of its normal temperature range.

9. Use the Appropriate Seal

Most new thermostats come with their own gaskets or rubber seal, but not all. So check that your new thermostat includes one; otherwise, 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 may damage an oxygen sensor and disrupt engine performance.

  • Some thermostats come with a rubber seal instead of a traditional gasket. Before installing, apply a light coat of fresh coolant to the seal.

  • Some models use a liquid gasket instead. Consult your repair manual, if necessary.

  • Verify that the mating surfaces on the thermostat housing and the engine block are perfectly clean.

10. Install the New Thermostat

Compare the new thermostat to the old one. Then, position the new one in place along with its seal, and tighten the housing bolts using a torque wrench.

  • Look for a marking on the thermostat indicating which end should face the radiator. If you can't find the marking, just make sure the spring (sensor) end faces the engine.

  • Also, some thermostats have locating pins that will help you to position the thermostat in the housing and block.

  • Your car repair manual specifies the torque value for the thermostat mounting screws. This will prevent cracking the 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—you can follow one of the bleeding procedures described in this post about how to change coolant, or check your vehicle service manual.

  • Trapped air will cause your engine to overheat. The next video gives you an idea about how to bleed the system in your vehicle as well, using a special funnel designed for this purpose.

  • Then, test your repair job by starting the engine and checking for coolant leaks and coolant level.

A Systematic Approach to Car Thermostat Replacement

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.

And here is a video that can also help you visually to complete your repair job.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

  • I changed my thermostat because my car was giving a code that said it was bad. Also, the heater stopped working but I wasn't having overheating problems. After changing it, the code still hasn't gone away and my heat still isn't working. Do you have any suggestions?

    Trouble code P0128 is usually related to a faulty thermostat, but a faulty intake air temperature (IAT) sensor, faulty radiator fan, bad engine coolant temperature (ECT) sensor and low coolant level can trigger this code. Make sure the heater is not clogged or leaking.

  • How long should I let the thermostat seal sit before I check for leaks ?

    It takes a few hours. But check the instructions that come with the product to be safe.

  • I changed my car thermostat, and now it overheats. This only happens when the engine is cool, and you drive like one or two miles. Once it overheats, I just loosen the radiator cap, and the car goes back to normal. What could be the problem?

    There could be air trapped in the system. Sometimes it is necessary to purge the thermostat system more than once.

  • I got my car thermostat replaced and had to fill the coolant three times. Is that normal?

    It is possible. When you first install the thermostat, it is closed. Then you try to top off the system, but there remain some air pockets that either you need to bleed or the system itself will 'burp', like in some newer cooling systems.

  • Do I apply the sealant for the thermostat replacement towards the motor?

    Yes, make sure the gasket is properly centered. Some gaskets come with an adhesive backing that will hold the thermostat in place, as well.

© 2014 Dan Ferrell


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    Post Comment
    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      3 weeks ago

      There could be a problem in the starting system, or you disconnected something by accident while replacing the thermostat. This other post may help:

    • profile image 

      3 weeks ago

      My 2007 VW Beetle Convertible

      Lives too far from costly dealer parts

      in Memphis TN area. Your topic re: coolant temp sensor replacement excellent in today's GOOGLE stories. I lost story. Also need coolant level sensor, maybe. Should I find that at Autozone when going for temp sensor? Realize Autozone not best source; only is nearby + 2 yr warrty. Hope your email gives me back your steps and photo for replacement. Thx, diane

    • profile image


      3 weeks ago

      I replaced the thermostat and. Now my car wont start

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      2 months ago

      Usually, most models place the thermostat with the valve anywhere within fifteen degrees of the 12 o'clock starting position.

    • profile image

      Richard Roe 

      2 months ago

      When you install the thermostat, does it have to be in a certain position or degrees on a 1999 Toyota Tacoma.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      8 months ago

      There could be air trapped in the heater core. Make sure you bleed the cooling system. This can lead to overheating problems. This other post may help :

    • profile image

      Thomas Robinson 

      8 months ago

      I changed my thermostat out on my car and I am not getting any heat.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      9 months ago

      Check for fuel pressure.

    • profile image


      9 months ago

      Cheaveys10 1987 replaced thermostat now it won't stay runing

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      20 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


      20 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 imageAUTHOR

      Dan Ferrell 

      22 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


      22 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 imageAUTHOR

      Dan Ferrell 

      24 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


      24 months ago

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

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      2 years 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


      2 years ago

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


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