Thermostat Symptoms, Function & Replacement

In Coolant by Magnus Sellén2 Comments


A thermostat manages the flow of coolant coming in and out the engine and the coolant temperature sensor records the coolant’s temperature by displaying it on the dashboard. This is some valuable information since without your car’s engine could very well be saying its goodbyes. There are two phases to a thermostat: it is either closed or open.

When the engine is sitting idle and it is relatively cold the thermostat will be closed but when the engine starts up and its temperature rises, the coolant’s temperature rises and so the thermostat opens up to let the coolant flow into the radiator, cool down and rejoin the coolant chamber inside the engine.

This mechanism ensures the car’s engine is operating at the prime temperature and that there is no overheating issue. Since the thermostat is a vital ingredient for the engine’s well-being, it’s proper working should be insured. The thermostat should close and open at the perfect time otherwise your car will start to develop serious troubles. Therefore, to know about the perfect time to go for a service read on the symptoms of thermostat failure.


Bad Thermostat Symptoms

The symptoms will give you a warning beforehand, so you can take the necessary precaution.

Bad thermostatOverheating Engine

Temperature Fluctuations

Possible Leakages

Replace Thermostat

Bleed coolant system

Replace Coolant

Overheating Engine

If the thermostat stays closed by accident, the coolant inside the engine will not be able to find its way through to the radiator and thus it won’t be able to cool off. This will result in the engine overheating -which you will be able to see in your dashboard with a rising temperature gauge ticker – and you won’t be able to drive for more than 10 minutes. Therefore, unexpected temperature rise means you need to visit the local mechanic.

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Temperature Fluctuations

The thermostat’s gate has to be timed to perfection to ensure the engine receives the coolant at the perfect temperature. Thus, if the timing is not right, you will experience fluctuating temperatures in your engine and your temperature gauge will act abnormally. This can also happen due to electrical failure, but you should never rule out thermostat failure from the equation.

Possible Leakages

When the thermostat does not work correctly, the hot coolant inside the engine’s coolant chamber finds a way to escape. We all know that hot air rises and that water when heated boils and forms vapor. When the coolant heats up it can attack the weak links and cause a leak. These leaks can be found in the piping that joins the radiator to the engine manifold. Leaks are very easy to spot since they can be seen visually

Rising Temperature and Full Radiator Tank

If the thermostat’s gate remains closed no coolant will be allowed to escape through to the radiator. The coolant inside will heat up and start to turn into vapour while the coolant inside the radiator will stay as it is. So, if you see the temperature gauge rising and the radiator tank full of water, you are most probably having a problem with the thermostat.


Solutions of a bad thermostat

There is not much you can do to solve a thermostat problem but you can make temporary fixes until you are able to get the thermostat repaired or replaced by a certified mechanic.

Replace Thermostat/Test It

The only solution for a bad thermostat is to replace it. The thermostat is often pretty easy to replace on the most car models. There is most likely no repair kit for your thermostat on your car, so you have to replace the whole unit. The thermostat is mechanically functioned and you can test it by put it down in a bucket of water and heat the water up to 90 degrees. If the thermostat is functional, you should see it open at this temperature (A bit different temperatures depending on the thermostat). If you want to find a thermostat for a good price, I recommend to check it out on Amazon here: Thermostats

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Bleed Coolant System

In many cases, you can misdiagnose a bad thermostat because of a bad bled coolant system. Make sure that you get all the air out from your coolant system.


Repair or Replace

The thermostat is a small component of the engine, so you do not have to worry too much about emptying your pockets just to get it repaired or replaced. However, it is always advisable that you save yourself from making the trip to the mechanic. Why should you spend money on repairs when you can save yourself from the trouble and just be cautious when dealing with your car? It is not like taking care of your car is difficult. The routine hardly requires 5 minutes every day, which we are sure everyone is capable of spending.

When it comes to the thermostat, make sure you regularly clean your car and take it for service every month, so that every electrical and mechanical component can get rejuvenated. Ensure you are regularly filling the radiator and the overflow tank and you will hardly see the temperature gauge rising. However, if the thermostat fails and the temperature gauge does rise, you are left with no choice but to spend money.


Thermostat Replacement Cost

Your mechanic will not ask too much in labour-related costs as the thermostat can be found easily in the most of the times. You would have to pay a standard $70 to $100 in labor costs to get your thermostat replaced or repaired. The repair can take a few hours, which is bearable considering you will be safe from any future troubles. However, if it comes to replacing the thermostat. You have other costs to consider.

Firstly, you or your mechanic has to find the right thermostat for your vehicle. Finding a matching part for a vehicle can be a hectic task and can sometimes take days. But sometimes, mechanics have a spare part available in their workshop that matches with your requirement, in which case you are to consider yourself lucky.
Now you can imagine what a rare part will cost you, probably a lot of money but an easily available part will not make much of a dent in your bank account. In reality, it could cost you around $100 to $200.

  1. Dear specialist

    You were talking about closed remained thermostat which makes over hot the engine.

    What about if there is not thermostat or the thermostat remained opened and the liquid circulates always via radiator. Whether this case is dangerous for engine? or if it is, so I have driven always like that, whether it has done any damage to my car engine? When I am driving on descent road in a speed 60 km/h then the temperature gauge ticker goes down slowly.

    Thank you

  2. My 5a engine opens fns at minml gauge yet abv checkedbout all connections what could be wrong

  3. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
    Ask A Mechanic

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