Car Thermostat Functions, Failure Symptoms and Replacement Cost


In this article we are going to explain about one important part in the engine systems and related to the cooling systems. This part called thermostat valve, so you will know the basic functions, failure symptoms and also the average replacement cost. And here we go:

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Basic Functions

The main function of a car thermostat is to control the amount of coolant that goes into the engine.  The thermostat will typically open whenever the engine starts to warm up. For example, when you’re driving your vehicle for a while, the engine will get hotter. This causes the thermostat to open and let the coolant flow right through the engine. That way, it will cool the engine off and prevent it from overheating. On the flip side, if you leave your car engine running while you’re parked somewhere, the thermostat will remain shut because the engine will already be cool from staying idle.

A functional thermostat will know when the right time to open because it has a sensor which detects the current operating temperature of the engine. As you operate your vehicle, the thermostat is normally open for most of the time because the engine needs to consistently be cooled off from the coolant. This sustains normal temperatures in the engine which helps it maintain the quality of its performance.

Of course, there are outside influences which may affect the temperature of the engine as well. The temperature of the environment around you is a perfect example of this. Cold and hot temperatures outside play a key role as to whether the thermostat is closed or open. But as long as you have a functional thermostat, then it will know when to perform either task.

Top 5 Failure 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 worn out or faulty. If you don’t do this promptly, then your engine could suffer irreversible damage the longer it is overheated.

Below are the top 5 symptoms that will indicate a failing thermostat in your vehicle.

  1. Temperature Change – The first noticeable symptom is when the temperature inside of your vehicle changes suddenly. It may start off by dropping to a very low temperature and then suddenly spike up to a very high temperature. Any change in temperature that doesn’t reflect your current air settings will mean that something is wrong with the thermostat.
  2. Coolant Leaking – A faulty thermostat will likely cause it to remain in its closed position. This means when the engine turns hot and the coolant 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 greenish liquid leaking out of your vehicle and staining the surface underneath, then you definitely have a coolant leakage situation.
  3. Engine Overheating – Most drivers are used to their temperature gauge showing a normal temperature. However, if you have a faulty thermostat, you will notice that needle in the temperature gauge moving toward the red area very quickly. This indicates that the engine is unusually getting hotter and it needs to be cooled off soon. This symptom should occur within 10 or 15 minutes of starting your engine.
  4. Rumbling Noises – 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 that you shouldn’t be hearing and you experience one of the other symptoms listed here, then you most certainly have a thermostat problem.
  5. Heater Malfunctions – If you live in a northern environment where it is colder outside, you may an opposite temperature problem in your vehicle. Sometimes when the thermostat is faulty, it could be stuck in the open position rather than the closed position. This means it will keep letting coolant flow into the engine, even when the engine doesn’t need it. If you’re trying to produce heat in the winter time and your thermostat is open, then you won’t get the heat that you want to warm yourself off.

Replacement Cost

For replacement parts, we recommend:

The good news for those with a faulty thermostat is that it does not cost a lot of money to have it replaced. Of course, the exact cost will depend on the make and model of your vehicle. But for the average car owner, you can expect to pay between $150 and $200 for a professional mechanic to replace the thermostat in your vehicle for you.

To break this average cost down, it is divided into parts cost and labor cost. The cost of the actual thermostat unit itself is between $30 and $60. The cost of the labor will be between $110 and $150. Remember that most mechanics will charge around $90 to $100 per hour for their services. The thermostat replacement job is not that timely, but it could take a mechanic about 1 to 2 hours to complete it. Therefore, you end up paying more money for the labor than you do for the actual thermostat part.

Read also: Diesel glow plug function, failure symptoms and replacement cost

A lot of car owners try to save money by replacing the thermostat themselves. Unless you are a professional or experienced mechanic, then you better let a professional do the replacement job for you. After all, there may be another problem with your vehicle as well. You’ll want a professional so they can first diagnose the problem before replacing the thermostat.


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