How to Tell If Your Car’s Thermostat Is Broken and What to Do to Fix It

When the heater is running in the car, it can feel great on a cold day – it thaws you so efficiently that you may have to take off your coat to stay cool. (Just make sure you don’t do this while driving.) What if you have heated seats? Mostly a trip to the spa. (Although instead of sipping cucumber-infused water, it’s a half-empty water bottle that’s been in your car for an unknown amount of time.)

So when your heat isn’t working, you notice. Aside from de-icing and fogging the windows , this is another “fun” part of driving in winter (in cold climates). There are several different reasons why you won’t have heat (Jonathon Klein lists seven of them in this article on The Drive ), including the most common cause of your lack of heat: a broken thermostat. Here’s how to tell if yours is broken and how to fix it.

How to tell if a thermostat is broken

While a faulty thermostat isn’t the only reason your heat isn’t working, Klein says he is most likely to blame. “A part stuck open or closed can cause problems not only with your heat, but also with your engine’s cooling system, ” he writes .

Aside from a general lack of heat, here are a few more signs that your thermostat might be breaking, courtesy of YourMechanic :

  • The temperature sensor shows very high values ​​(red) for the first 15 minutes after starting the engine.
  • The engine has been sitting for a long time and has not warmed up.
  • Vehicle temperature varies unevenly.
  • Coolant leaking from the thermostat housing or from under the vehicle.

How to fix a broken thermostat

Fortunately, this is a relatively straightforward job that you can probably do on your own, and Klein provides a set of easy-to-follow instructions .

Safety first: he recommends the mechanic’s goggles and gloves. Now, here’s what else you need :

  • Drain bucket
  • Selection of wrenches
  • Coolant
  • New thermostat
  • A flat workspace (such as a garage floor or driveway)

Here’s what to do :

  1. Let the machine cool down for 15-20 minutes.
  2. Find a thermostat. It will be at the base of the radiator, between the core and the main hose.
  3. Remove the radiator cap.
  4. Raise the front of the vehicle for better clearance.
  5. Place a bucket under the radiator and drain the coolant by disconnecting the hose.
  6. Remove and replace thermostat.
  7. Connect the hose to the radiator.
  8. Add coolant and close the reservoir with the lid.
  9. Lower the car.
  10. Start the engine.
  11. Wait to see if the heat comes on.
  12. Take a test drive.
  13. Make sure the coolant level has not dropped.
  14. If so, top up as needed.

Now enjoy the warm and hot ride.


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