Bad Thermostat Symptoms And Thermostat Replacement Costs

A car thermostat is a basic yet critical component of an automobile. It aims to manage the flow of coolant, allowing the engines to keep a constant temperature throughout different circumstances.

If the component fails, the thermostat will often be “stuck open” or “stuck closed.” Harm to the engine is possible in both circumstances (particularly the latter).

This article will discuss the fundamental operations of a thermostat, frequent signs of a defective thermostat, and the usual expense of replacing a thermostat if it fails.

How a Car Thermostat Works

The thermostat plays an important part in an engine cooling system. It controls the circulation of coolant between radiators and the engine. Although it is tiny, the role it does is vital for keeping your engine at a safe and secure working temperature.

Excessive heat for too long might result in a broken engine block or a burst head valve. Excess heat is picked up when coolant passes through the engine. It travels from the engine to the coolant, in which the excessive heat is eliminated. It then performs a little pause as it travels through all the cooling systems before returning to the engine.

Close-up photo of the car thermostat valve.

The thermostat is simply a valve that connects the engines to the radiators. When the coolant in the engine becomes too hot, this valve opens, allowing it to flow to the radiator to chill. If it is not warmed, the thermostat remains closed, letting coolant circulate within the blocks.

Car Thermostat Replacement Cost

Depending on the automobile type and labor expenses, the typical thermostat repair costs around $80 and $400. A thermostat costs between $30 and $80, while the labor at a workshop costs between $150 and $400.

Some vehicles have complete housing that includes the thermostat, making it hard to replace thermostats separately. It can raise the cost of the part substantially. On some vehicles, the thermostat is installed incorrectly, necessitating many hours of labor. However, on others, it may be replaced in less than ten minutes.

Read a service handbook to see how much labor it takes to change the thermostat on your specific vehicle.

Bad Thermostat Symptoms

When your automobile thermostat malfunctions, it affects the performance and functioning of your engine. Luckily, when this occurs, you will observe several identifiable signs.

If your thermostat becomes defective or leaks, you must repair it as soon as possible. If you do not act quickly, your engine may endure permanent damage the more it remains overheated.

The following are some of the most common symptoms of a broken thermostat in your car.

1.     Unusual Temperature Readings

When you start your car after a lengthy break, you will normally observe that the temperature reading starts chilly and gradually rises to the midpoint, which is the optimal engine temperature.

However, if the thermostat fails, the coolant’s circulation to the radiators will be reduced. It implies that if the thermostat is kept open, the temperature will keep increasing alarmingly. If the thermostat is left open, the temperature will most certainly stop when approaching the mid-point.

When the thermostat is jammed closed, it prevents coolant from running into the engine. It implies that your temperature gauge will keep rising until it reaches the hot end of the scale. If you keep driving your car at that moment, you intensify your risk of engine damage.

That is why it’s essential to keep track of the engine temperature indicator at all times. When you observe the rising temperature above usual, it’s a smart decision to stop for a while and let the vehicle cool down.

2.     Coolant Leaks

When a thermostat malfunctions, it frequently stays in the closed position. As the engine overheats, coolant will leak from the thermostat housing. It implies that coolant seeping from your engines might indicate that your thermostat has failed. It might also hint at problems with your radiator’s lines, the radiator structure, or the valves and cylinder liners.

Green coolant leaking from the radiator.

If you don’t do anything to fix it, your coolant pipes will be the next to leak. Check beneath your car to discover whether you’re leaking coolant. If you notice greenish or reddish liquid coming from your car and staining the area below, you have a coolant leak.

3.     Strange Noises

Strange noises are another indicator that your thermostat is failing. You may experience growling noises from the vehicle, which might be coming from the radiators due to heating coolant. It might also sound like boiling water or pounding. The sound might also be bubbling at times. All of this indicates an issue with your cooling system.

4.     Heater malfunction

If you live in a cold environment, your thermostat may be left open instead of closed. It implies you will encounter a heater malfunction instead of overheating. It means the coolant will circulate to the engine even if it is not required. If you reside in a cold place or drive throughout the winter, remember to check your heater too.

5.     Rust and Deposit Formation

This symptom demands some expertise with what’s under the engine of your vehicle. If your car thermostat is rusted or blocked when you inspect your engine cooling system, it is an indication that it will fail shortly.

Replace the thermostat if it is rusted or blocked to avoid engine harm. Selecting the proper coolant for your vehicle can help protect the cooling system and increase the lifespan of the thermostat.


Properly functioning thermostats help in maintaining the engine’s maximum operational efficiency. When a vehicle is cold, it consumes additional gas since gas does not evaporate as effectively as it is warmed. The coolant must take considerable time in the radiator section to be cooled by the fan and air before being transferred to the engine compartment for use in the cooling system.

Many individuals assume that removing the thermostat from their vehicle would help it run cooler. It’s the opposite. Without the thermostat, the coolant will run through the radiators quickly, not giving enough time to cool down, perhaps causing damage to the engine.

If you discover that your thermostat is broken, have it repaired as soon as possible so that it does not cause major harm to your car and cost you more money in the long run.

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About Matthew Webb

Hi, I am Matthew! I am a dedicated car nerd! During the day, I am a journalist, at night I enjoy working on my 2 project cars. I have been a car nerd all my life, and am excited to share my knowledge with you!

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