How does Thermostat work?

A thermostat is a most important part of the engine cooling system. It works according to the engine temperature. It uses to control the coolant flow entering and leaving the engine. The efficient working of the thermostat prevents the engine from overheating and many other problems. As the thermostat goes bad, it generates various symptoms. This article mainly explains the signs, replacement cost, and location of the thermostat.

What is Thermostat?

A thermostat is a part of the engine cooling system that closes and opens to permit coolant to flow in and out of the engine. It acts as a valve that activates according to the temperature of the engine. The thermostat activates as the engine temperature increases and allows coolant to flow from the radiator to the engine.


Symptoms of Bad Thermostat

As the thermostat goes bad, it generates one of the below-given symptoms:

  1. Engine Overheating
  2. Temperature Fluctuations
  3. Heater Fluctuation
  4. Coolant Leaking
  5. Rumbling Noises
  6. Rising Temperature and Full Expansion Tank

1) Engine Overheating

The engine overheating is one of the main signs of a bad car thermostat. The thermostat works as a valve that allows the coolant to flow from the radiator to the engine and vice versa. When the engine temperature increases, the thermostat opens and allows the coolant to flow throughout the engine.  

As the vehicle thermostat fails, the coolant cannot flow to the engine, and the vehicle will eventually overheat. Therefore, when your vehicle overheats, immediately check your thermostat, and if it goes bad, then fix it.

2) Temperature Fluctuations

The thermostat must be opened and closed according to the engine requirements so that engine can properly maintain its temperature. The perfect timed opening and closing of the thermostat ensures the proper supply of the coolant to the engine and maintains the normal temperature of the engine.  

If the timing is wrong, you will see a fluctuation in the engine temperature, and the temperature gauge will respond abnormally. The temperature gauge is installed on the vehicle dashboard.

You may also face temperature fluctuation issues due to power or air faults in the cooling system.

3) Heater Fluctuation

The car heater takes heat from the hot coolant of the radiator. As the heater extracts heat from the coolant, it transfers this heat inside the car. Therefore, when the thermostat is not working properly to keep the car’s engine at a constant temperature, the heater will not work properly, and you may face temperature fluctuation issues.  

When the thermometer and the heat in the car are fluctuating, it’s the best time to check the thermostat.

Temperature changes that do not reflect current HVAC settings usually indicate a problem with your car thermostat.

4) Coolant Leaking

As the thermostat fails, it gets stuck in the off position. This means that when the thermostat is stuck in the closed position, the coolant will not flow to the engine. This causes the coolant to leak out of the thermostat casing.

If it is stuck in the closed position and you don’t fix it, then ultimately, your coolant hose will be leaked. The easiest method to check for coolant leaks is to look under the vehicle. If the vehicle is leaking green or red liquid and the underlying surface is dirty, there is definitely a coolant leak.

5) Rumbling Noises

The rumbling noise from the vehicle is one of the obvious signs of a stuck thermostat. The vehicle may generate rumbling noise due to a fault in the radiator, the engine, or both. So, if you are hearing this kind of noise or noticing the old car thermostat symptoms, there are high chances that you have a bad thermostat.

6) Rising Temperature and Full Expansion Tank

In the case of a closed thermostat, the coolant can’t flow from the radiator to the engine. In such a condition, the coolant in the radiator remains the same, but the coolant inside heats up and begins to turn into vapor.

Therefore, if the temperature gauge goes up and the radiator reservoir is filled with coolant, it means you may have a faulty thermostat.

What causes a thermostat to fail?

1) Engine Overheating

The thermostat works according to the temperature of the engine. It opens and closes according to the engine heat. If your engine overheats due to some reason, the thermostat may fail. Thermostat parts are manufactured to work at normal operating temperatures of the engine, while excessive overheating can damage these parts.

2) Sludge

With time, the coolant contaminates and begins to fail. The major problem is that the coolant condenses and converts into thick, sludge-like material with time. This sludge can enter the thermostat and restrict or completely block the flow. The contaminated coolant can also prevent the thermostat from giving correct readings, causing delays in closing and opening, which may cause engine overheating or hypothermia.

3) Defect

Like many other car parts, thermostats are mass-produced in factories. Before the thermostat goes on sale, the manufacturer inspects its efficient working. Human factors play an important role in controlling the behavior of thermostats. During the inspection process, the manufacturer may miss some defects that may cause of a bad thermostat.

4) Maintenance

The proper repair and maintenance of the thermostats are very important for their efficient working. If you don’t maintain the thermostat properly, it will not work properly and may lead to different issues.

5) Age

Age is another common cause of failure. The thermostat heats up and cools down all the time, and internal parts can wear out over time. This usually happens slowly, but the temperature at which the thermostat opens will start to rise until, one day, total overheating occurs.

Thermostat Replacement Cost

The thermostat replacement cost varies according to your living area, type of brand, and the car model. The average replacement cost of the thermostat is between $60 and $470. In this cost, the labor cost is from $40 to $380, while the thermostat cost is between $20 and $90.

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