How to Fix a Temperature Gauge

Like Katy Perry sang, your car is “hot and then cold.” Let's fix that.

Depositphotos

The Drive and its partners may earn a commission if you purchase a product through one of our links. Read more.

So your car’s temperature gauge is acting up, or not working at all, and you want to fix it? Good for you. Your car’s engine temperature is vital to its operation, and a properly-operating gauge is a window to its health. Plus, it could mean the difference between getting to work and being stranded in a deserted mining town as zombies size up your brain. Anyway...

In modern cars, the temperature gauge also helps the engine computer set a proper fuel-to-air mixture. That's important for both fuel economy and engine longevity. But figuring out what’s causing your temperature gauge to fail, or behave erratically, isn’t just a case of “here’s what’s wrong.” It will likely take some troubleshooting. The Drive’s crack How-To team is here to help you diagnose and fix your temperature gauge, and get back on the road.

Let's get started.

Basics

Estimated Time Needed: One hour or more

Skill Level: Intermediate

Vehicle System: Cooling

Depositphotos

Safety

Working on your car can be messy, especially when you’re working with surfaces you’ve never bothered to clean before. It can also be dangerous as liquids can be scaldingly hot and parts could fall on your toes. So here’s what you’ll need to ensure you keep your jeans, shirt, and skin spotless, and your bones fully intact.

  • Mechanic gloves.
  • Long-sleeve shirt to protect your arms.
  • A mask or ventilator to prevent inhaling chemical fumes, and if you want to look like a cut-rate Bane.
  • Eye protection.

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking, though check your local laws to make sure you’re not violating any codes when using the street.

Depositphotos

Everything You’ll Need

We’re not psychic, nor are we snooping through your toolbox or garage, so here’s what you’ll need to get the job done. 

Tool List 

Parts List 

  • New temperature sensor (if applicable)
  • New thermostat (if applicable)
  • New coolant
Depositphotos

Here’s How to Fix Your Car’s Temperature Gauge

Let’s do this! 

Replacing a Faulty Engine Coolant Temperature Sensor

The most common cause of faulty temperature readings is a broken coolant temperature sensor (CTS). The part, which is normally located near a vehicle’s thermostat near the base of the radiator (consult your owner’s manual or repair guide) can get gunked up and fail. 

  1. Using an OBD2 scanner, check to see if the CTS is providing live temperature readings.
  2. If it isn’t, there’s your problem. The part will need to be replaced.
  3. Let the car’s coolant cool for 15 to 20 minutes.
  4. For better clearance, lift up the front end of your vehicle.
  5. Remove the radiator cap.
  6. Drain the radiator, according to instructions in your car's repair manual.
  7. Disconnect the temperature sensor's wiring connector.
  8. Remove the temperature sensor.
  9. Install the new temperature sensor.
  10. Reconnect the wiring connector.
  11. Make sure all the coolant plugs are secure.
  12. Add coolant and place the cap back on the reservoir.
  13. Lower your car.
  14. Start the engine.
  15. Wait to see if the temperature gauge reads correctly.
  16. Take a test drive.
  17. Check to make sure the coolant level hasn’t dropped.
  18. If it has, refill it as necessary.
  19. If everything is a-ok, you’re golden.
Depositphotos

Replacing a Faulty Thermostat

The second most common fault is a bad thermostat. This little part manages the flow of coolant from the radiator to and from the engine and can become stuck open or closed. Neither is a good thing for your engine. The thermostat is usually located at the top of the radiator or at its base (consult your owner’s manual or repair guide). The only way to test a thermostat is by removing it completely and submerging it in a bucket of hot water to see if it opens. Here’s how to test and replace a faulty thermostat.

  1. Let the car’s coolant cool for 15 to 20 minutes.
  2. Locate the thermostat.
  3. For better clearance, jack up the front end of the vehicle.
  4. Remove the radiator cap.
  5. Drain the radiator, according to instructions in your car's repair manual.
  6. Remove the thermostat. 
  7. To test the thermostat, submerge in near-boiling water. If it remains closed, it’s faulty and should be replaced. 
  8. Replace thermostat.
  9. Make sure all the coolant plugs are secure.
  10. Add the coolant and place the cap back on the reservoir.
  11. Lower your car.
  12. Start the engine.
  13. Wait to see if the temperature gauge reads correctly.
  14. Take a test drive.
  15. Check to make sure the coolant level hasn’t dropped.
  16. If it has, refill it as necessary.
  17. If everything is a-ok, you’ve done it.

Diagnosing Air in the Coolant System

Another common reason for a faulty temperature gauge is air making its way into the radiator hoses. Air can pool near the temperature sensor or the thermostat and cause faulty readings (or no readings at all). It can also affect the car’s overall cooling efficiency. Here’s how to diagnose and to fix air in your hoses.

  1. Jack up the front of your car, this will aid the air removal.
  2. With the radiator cap off, start the car.
  3. Coolant should begin to cycle through the engine and if there’s air trapped in the system, it will burp up the air. 
  4. Let the car idle until warm, which may take 15 to 20 minutes. 
  5. Once you’re satisfied all the air has been removed (the burps will stop), replace the radiator cap.
  6. Lower your car.
  7. Take a test drive.
  8. Check to make sure the coolant level hasn’t dropped.
  9. If it has, refill it as necessary.
  10. If everything is a-ok, you’ve done it.

Diagnosing a Faulty Instrument Cluster

The average DIY’er may need a professional to diagnose and fix a faulty instrument cluster. If you’ve already checked the three possible culprits above and none were the cause, it’s more likely something is wrong with the gauge cluster itself. 

Depositphotos

Tips From a Pro

Here are our top pro tips to help you diagnose and fix your temperature gauge.

  • If you see a dip, or even a fluctuation, in your fuel economy, you may have a faulty temperature sensor or thermostat; both aid the car’s ECU in determining how much fuel goes into the engine. 
  • A check engine light may also tell you that something’s amiss. The same with leaking coolant.

Life Hacks

Since you may not have access to the right tools, we also compiled a list of our best hacks to make your life easier and drain your pocket less.

  • If you’re stuck by the roadside with a radiator leak and only a grocery store in sight, you can plug the leak by pouring an uncooked egg white into the radiator filler hole (don’t use the yoke; it can plug up the heater core). This should only be done in an emergency, but it works. 
  • If your car is overheating, turn on your heater and open up the windows. The heater will help dissipate the heat from the engine. 

How Often Do You Need To Replace Your Thermostat or Temperature Sensor?

Automakers build these parts to survive and often you won’t know it’s time to replace one until it fails.

How Often Do You Need To Flush Your Radiator?

About every 30,000 miles or every third oil change for most modern cars.

Featured Products

Ancel AD310

Evans High-Performance Waterless Engine Coolant

K-Seal Multi-Purpose One Step Permanent Coolant Leak Repair

Got a question? Got a pro tip? Send us a note: guidesandgear@thedrive.com