Car Thermostat Replacement: 10 Important Tips

Updated on July 16, 2018
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, like:

  • 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.

Index
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

Warning!

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.

Questions & Answers

  • What is a good tip to assure that the thermostat is always facing the right way? The coolant usually flows top to bottom of the radiator, right? So which end would I want facing the flow?

    Have the spring face the engine; the pointy side towards the radiator.

  • 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.

  • Does a thermostat have a serial number one can use to identify a specific one for each car?

    Not necessarily. One serial number may apply to more than one model. If you want to be absolutely sure you're getting the correct replacement, you can use your car's VIN number located on your registration card or the interior of the dashboard, driver side.

© 2014 Dan Ferrell

Comments

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    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      6 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 

      6 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 

      8 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 

      8 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.

      Thanks.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      9 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 

      10 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 

      12 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 

      12 months ago

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

    working

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