How to Tell If Your Car's Thermostat Is Broken

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Step 3 Replace the Thermostat

Take the old thermostat out and be sure to note which way it was facing originally. You can use the putty knife to remove any glue remains that were left over from the previous thermostat. Once the surface is cleaned, apply the new glue to the gasket and insert the new thermostat in the same manner as the original you removed. Allow it to remain in place long enough for the glue to set. Once it is firmly in place you can replace the housing and bolt it back into place just as you found it.

Bad Thermostat Symptoms

When your car thermostat fails, it will impair the operation and functionality of your engine. Fortunately, there will be some easily recognizable symptoms that you will notice when this happens.

You should take it upon yourself to replace your thermostat promptly if it turns out that it’s faulty or develops a leak. If you don’t do this promptly, then your engine could suffer irreversible damage the longer it is overheated.

Below are 5 of the most common signs that will indicate a faulty thermostat in your vehicle.

See Also: Symptoms of a Bad MAP Sensor

#1 – Temperature Gauge Reading Higher (or Lower) Than Normal

When you first start your car, the needle in the t

When you first start your car, the needle in the temperature gauge should be in the Cold side if the car has been sitting for a while. As you’re driving, you’ll normally notice the temperature gauge gradually creeps up until it reaches about the midway point in the gauge, which is the optimal engine operating temperature.

In the situation where the thermostat is stuck closed, it will prevent coolant from flowing into the engine. This means that your temperature gauge will continue rising until it’s all the way to the Hot end of the gauge. If you continue driving your vehicle at that point, you increase your chances of engine damage the longer you drive.

This is why it’s important to always keep an eye on the engine temperature gauge. As soon as you notice the temperature going higher than it normally does, it’s a good idea to pull over to allow the engine to cool down.

In cases where the thermostat is stuck open, you’ll notice that the temperature needle moves up much slower than usual and likely stops before it gets to its normal mid-point on the gauge. If you notice this, try cranking up your heater and if it doesn’t blow warm air out of the vents, you’ve pretty much confirmed a broken thermostat.

#2 – Sudden Air Temperature Changes Inside Vehicle

One symptom that you can often feel is when the ai

One symptom that you can often feel is when the air temperature inside your vehicle suddenly changes. It may start off by dropping to a very low temperature and then suddenly spike up to a very high temperature.

Any change in air temperature that doesn’t reflect your current HVAC settings will often mean that something is wrong with the thermostat.

#3 – Coolant Leaking

A faulty thermostat most likely causes it to remai

A faulty thermostat most likely causes it to remain in its closed position. This means when the engine is running hot and the coolant normally flows toward it, the closed thermostat will block the coolant from going into the engine. This will cause the coolant to overflow from the thermostat housing.

If it stays like this and you don’t do anything to fix it, your coolant hoses will be the next things that leak. The quickest way to see if you’re leaking coolant is to just check under your vehicle. If you see green-ish or red-ish liquid leaking out of your vehicle and staining the surface underneath, then you definitely have a coolant leakage situation.

#4 – Rumbling Noises

If temperature changes were not bad enough, you wi

If temperature changes were not bad enough, you will begin hearing strange rumbling noises as well. These noises will be coming from your radiator, engine, or both. The noise could also resemble a knocking sound, boiling sound, or gurgling sound as well.

Basically, if you’re hearing strange noises as described above and you experience one of the other symptoms listed here, then you most certainly have a thermostat problem.

#5 – Heater Malfunction

If you live in a cooler climate or are driving aro

If you live in a cooler climate or are driving around in the middle of winter, you may an opposite temperature problem in your vehicle. Instead of being in a stuck closed position, it will be stuck open.

This means it will keep letting coolant flow into the engine, even when the engine doesn’t need it. So if you turn the heater on inside the vehicle cabin and thermostat is open, then cool air will continue to come out of the HVAC vents even when you turn up the heater temp all the way. You won’t get the heat that you want to warm yourself up.

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Part 4 of 4 Replace the coolant

Materials Needed

A properly maintained cooling system will help extend the life of the thermostat, but it will also help maintain the other supporting components as well. Not only should you have your thermostat checked, but be sure to also have your coolant replaced according to the manufacturer service maintenance intervals to keep that thermostat running great.

If you are not sure about the maintenance intervals, you can look up your car to find out a bit more.

Step 1: Test the coolant. You can use a coolant te

Step 1: Test the coolant. You can use a coolant tester to test a sample of the coolant in the radiator.

The coolant tester will determine if the coolant is able to do its job and not freeze inside the system when ambient temperatures fall below 32F. Read the instructions for your tester to determine exactly how to read the results you get.

Step 2: Test for corrosion. You can also use a digital multimeter to test the coolant for corrosion.

Corrosion can and will prematurely aid in cooling system failure, specifically the water pump, radiator, heater core, and finally the thermostat.

Step 3: Open the radiator cap. To use your digital multimeter, start with a cool engine and open the radiator cap.

  • Warning: Never open the radiator cap when the engine is hot to help prevent burn injuries.

Step 4: Allow the engine to idle. With the cap off, start the engine and let it idle at 1500 RPMs to warm up.

Step 5: Place negative probe on terminal. After a few minutes, take your multimeter, set it to DC voltage and place the negative probe on the negative battery terminal.

Step 6: Dip positive probe in coolant. As for the

Step 6: Dip positive probe in coolant. As for the positive probe, go ahead and dip that right into the coolant.

If the meter reads .4 volts or less, the coolant is good; however, if it reads more than .4 volts, then the additives in the coolant that prevent electrolysis have broken down, which means the coolant should be replaced.

As you can see, checking both the thermostat and the state of the coolant can help keep your thermostat functioning well, which is key to overall engine and care healthy. Have one of YourMechanic’s technicians have a look over your vehicle and perform a thermostat replacement if needed.

Can I still drive my car if the thermostat is broken

Answered By: Jack Parker Date: created: Dec 10 2021

If it is failed in a closed position then you cannot really drive it with the thermostat broken, as the engine would overheat. … This however will not generally have any impact on the ability to drive the car, at least if you let it warm up before you start driving.

Asked By: David Perry Date: created: Dec 27 2020

How to Test a Car Thermostat

Checking your car thermostat is the best way to know if the unit has actually failed. The testing procedure requires a kitchen thermostat and a pair of needle nose pliers. First, you need to remove the thermostat from your car.

The thermostat housing is accessible in most cars, but you still need to follow some precautions that might apply to your particular model. If you need more help, the best way is to follow the instructions in the repair manual for your particular vehicle make and model.

Once you have removed the thermostat from your car:

  1. Visually inspect the thermostat. It should be in the closed position. If it is opened, replace it.
  2. Place a kitchen pot on a stove. Pour enough water into the pot to cover the thermostat.
  3. Submerge the thermostat in the kitchen pot, but don’t let it touch the bottom of the pot. Use a pair of needle nose pliers for this.
  4. Start heating the water and place the kitchen thermostat in the pot, but don’t allow the thermostat to touch the pot. You just want to monitor the water’s temperature.
  5. Watch closely and notice at what temperature the thermostat begins to open.
  6. Make a note of the temperature at which your thermostat began to open.
  7. Wait for the thermostat to open completely and make a note of the temperature. Then, remove the thermostat from the pot and check that the thermostat gradually closes completely.
  8. Compare your notes to the thermostat operating temperature specifications in your vehicle repair manual. If your thermostat deviates from the specifications, or the thermostat mechanical action deviates from the one described above, replace it.

Most vehicle engines operate at a temperature range of approximately 195–220 ºF (91–104 ºC). Check your vehicle repair manual for the thermostat operating range, and make sure you have the correct one for your application. Or replace it, if necessary.

The next video gives you an idea about replacing a thermostat in a car.

How Do I Know If My Car Needs a Thermostat?

Now that you have an idea of how the thermostat operates, you can use that knowledge to investigate the problem.

  • First, open the hood and make sure the engine and radiator are cool.
  • Then, locate the thermostat. If you follow the upper radiator hose towards the engine, you will see the end of this hose connecting to the thermostat housing. Inside this housing resides the thermostat. On some vehicle models, though, the thermostat housing connects to the lower radiator hose.
  • If you need help to locate the thermostat, consult your vehicle service manual. You can buy one at your local auto parts store or online. You could also check the reference section of your public library.
  • Once you’ve found the thermostat, perform one of two simple tests: If you have access to the radiator cap on your car, use the following troubleshooting procedure: Checking Coolant Flow. If the radiator cap is not accessible, or you don’t see the cap, go to the next troubleshooting procedure: Checking Coolant Temperature.

Some Recommendations Before You Start:

Even if your radiator cap is accessible, you can actually do both tests, since neither requires removing the thermostat from your car and they both only take a few minutes.

With an overheating engine problem, it’s a good idea to have an assistant behind the wheel to shut off the engine if the temperature reaches an unsafe level while testing.

If either of your tests points to a bad thermostat, follow up with the third procedure below, How Do I Test a Car Thermostat, to test it outside of the vehicle and make sure you need to replace it.

If you are performing one of these tests because your engine is overheating, it’s a good idea to have an assistant behind the wheel to shut off the engine if the temperature reaches an unsafe level while you do the test.

How do I know if my thermostat is working properly

Answered By: Landon Roberts Date: created: Jan 05 2022

The most common signs of a broken thermostat are:Thermostat display is off or is non-responsive.Turning on the heat or AC does nothing.The heat or AC will come on, but either stays on nonstop or cuts out before the temperature setting is reached.

Asked By: Albert Martin Date: created: Jan 03 2021

Part 2 of 4: How to tell if the thermostat is faulty

Step 1: Check your gauge. If you see your temperat

Step 1: Check your gauge. If you see your temperature gauge going into the red within the first 15 minutes of driving, your thermostat may be bad.

Generally, if your vehicle is overheating within 15 minutes or so of driving it, this may be a sign that the thermostat is stuck.

Step 2: Check the radiator hoses. If you notice that the engine is hot but the radiator and the upper radiator hose are cool to the touch, there may be a thermostat issue.

Both hoses should be warm to hot. If one hose is cold and the other hot, this is a good indication your thermostat is stuck closed.

How to Fix a Broken Car Thermostat in 8 Simple Steps

What you’ll need:

  • Safety gloves
  • Safety goggles
  • Car jack and stands
  • A suitable container to catch the coolant, which is toxic
  • Wrenches
  • New coolant
  • New thermostat

What to do:

Step 1: Make a safety assessment

Ensure you’ve done your health and safety checks. Is the vehicle in a driveway, garage, or other safe space, and on an even surface to carry out the work? Have you got adequate clothing, gloves, and goggles (a must when you’re dealing with antifreeze)? Is the car engine cool? If you’ve just used the car, you’ll need to wait until the engine’s cold.

Step 2: Drain the coolant

Use the car jack and stands and carefully raise the car. Place the container underneath the radiator where it will catch the draining coolant, and then remove the radiator plug. Once the coolant has all drained, replace the plug.

Step 3: Lift the front of the car and find the thermostat

Consult the owner’s manual and identify where the thermostat is in your car. In most vehicles, it’s located at the base of the radiator and best to access it from underneath after lifting the front of the vehicle.

Step 4: Replace the thermostat

Take out the old broken thermostat and install the new one. A new thermostat will cost in the region of $45. Not ideal, but a relatively small price to pay for comfortable and safe driving.

Step 5: Add new coolant

It’s the perfect opportunity to change your coolant—one of those jobs you don’t get around to as much as you probably should. To do this, start by cleaning, or ‘flushing’, the system with rinsing fluid. Fill the radiator with it before draining it as you did with the coolant. Then add your new coolant.

Step 6: Lower the car

Taking lots of car, lower the car from the stands using the jack.

Step 7: Do some simple checks

Drive around and try out the heater. You should hopefully find it comes on and stays at a stable temperature with no problems. Check the engine temperature dial, looking for signs of overheating. You can also go back and check the coolant level after a couple of days (and when the engine is cold) to make sure you haven’t got a leak. If any problems persist, speak to a trusted mechanic without delay.

Step 8: Wash your equipment and dispose of the old coolant safely

Last but not least, you must be careful to wash any toxic coolant off your clothing, gloves and hands, and of course dispose of the old, contaminated coolant according to local guidelines.

About This Article

Co-authored by: Hunter Rising wikiHow Staff Writer This article was co-authored by wikiHow staff writer, Hunter Rising. Hunter Rising is a wikiHow Staff Writer based in Los Angeles. He has more than three years of experience writing for and working with wikiHow. Hunter holds a BFA in Entertainment Design from the University of Wisconsin – Stout and a Minor in English Writing. This article has been viewed 5,503 times. 1 votes – 100% Co-authors: 4 Updated: January 23, 2022 Views: 5,503 Categories: Car Maintenance and Repair

Thanks to all authors for creating a page that has been read 5,503 times.

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