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Car Care Advice

5 Bad Thermostat Symptoms To Look out For

August 19, 2022
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Your car’s thermostat isn’t just to gauge heat. It contributes to your engine’s overall function, timing the release of coolant to keep your car running as effectively as possible. If you haven’t serviced your thermostat, or replaced it within the last ten years, it may be time to do just that. 

Read on to learn more about the bad car thermostat symptoms you should watch for, and learn more about convenient at-home thermostat replacement options. 

1. Check engine lights & codes 

Your check engine light may be one of the first symptoms of a bad thermostat that you’ll notice – illuminating on the dash with or without an associated code. You may also see a P0128 error code, which is shown when your engine is having trouble regulating temperature. This is normally attributed to a bad thermostat or issues within the engine control module. This code often indicates that the engine is running too “cold” due to your thermostat’s malfunction, meaning that your car is unable to properly prepare, heat, and disperse the coolant into the engine. 

2. Coolant leaks 

When your thermostat stops working, you may notice a higher incidence of coolant leaks. This happens when your engine runs at too high of a temperature due to the dysregulation, causing an overflow of coolant into the surrounding areas. This can result in a “sweet scent” when you operate the vehicle, or white smoke. 

While this can be a sign of a broken vehicle thermostat, you may want to also check for head gasket sealant issues or breakages, since this can result in similar symptoms. 

3. Incorrect gauge reports 

You likely reference your temperature gauge multiple times as you drive – making this one of the most common ways to spot a broken thermostat. If you notice frequently high or low readings that are out of the norm, it may be time for a vehicle thermostat inspection. Taking the time to be seen when the problem begins can save you significant cost and time later. 

4. Rumbling or knocking noises 

If your thermostat isn’t functioning properly, your coolant may be reaching too high of a temperature – resulting in leaks. It may also hit boiling point, which can result in a banging or rumbling sound coming from your engine bay. This will be noticeable as you drive, and can worsen as you accelerate. If these noises are paired with a sweet, burning scent or white smoke coming from your exhaust, it could be a result of a thermostat-related coolant leak. 

5. Inefficient heater function 

If you’re having issues heating your car, it may not just be the change of season. Thermostat malfunction can cause inefficiencies in your vehicle’s heating system, especially if the thermostat is frozen in the “open” position of function. If you notice issues heating your car consistently, or hear a “knocking” if you try to turn on your vehicle’s heater function, that could be one of the most common symptoms of a bad thermostat for your vehicle – and you should get it checked out. 

What happens when a car thermostat goes bad? 

When your car’s thermostat goes bad, it will not properly register your engine’s temperature, which will result in a lack of coolant flowing to the engine. This can lead to overheating and other related problems; such as a coolant leak. If you’re experiencing symptoms of random coolant leaks or heater insufficiency, you may want to take your car for a professional evaluation. It could be a faulty thermostat unit. 

What would a bad car thermostat cause? 

A bad car thermostat can result in overheating and heater insufficiency. While these don’t seem serious, these symptoms of a bad thermostat can lead to permanent engine damage due to excessive heat – such as seal breakages, cracked elements, and engine detonation. 

How do you know if your car thermostat is working? 

If your vehicle is under ten years old, it’s likely that your thermostat is working perfectly fine. Vehicle thermostats have an average lifespan of a decade, so those who drive older models should consider investing in an inspection and possible thermostat replacement. 

If you feel comfortable testing your car’s thermostat function at home, here are a few steps to do so:

Convenient auto repair at home 

Looking for a convenient auto repair solution? Consider the team at RepairSmith. Our experts come to your home and take care of vital services your car needs to function properly. For more information, please connect with us today.