Symptoms of A Bad Thermostat and Replacement Cost

bad thermostat symptoms

The thermostat is a useful and important part of the coolant assembly for an internal combustion engine, helping to maintain normal engine temperature and being responsible for the operation of the heater in the cabin. Without a thermostat, a vehicle’s engine remains cold even over long distances or long periods of time, and running the engine cooler than normal for long periods of time can be detrimental to performance and engine oil.

Because running the engine at temperatures that are colder than normal for a long time daily can cause engine oil depletion, if not taken care of in time, the oil level in the engine can be very low, which can cause the engine to overheat or, in many cases, the engine seize.

What Is Thermostat In Engine?

The thermostat is an important device in the engine’s cooling system that controls the temperature within the desired range by activating or deactivating the heating or cooling system. It detects the current temperature of the engine and compares it to the set point, allowing actions such as turning on the heater or air conditioner in the vehicle cabin.

Symptoms of A Bad Thermostat

Symptoms of a bad thermostat include engine overheating or overcooling, coolant leaks, an unstable temperature gauge, unusual engine noise, erratic operating temperatures, or cabin heat problems.

Let’s take a closer look at the symptoms of a bad thermostat so you don’t get confused about one when the engine overheats.

1. High Temperature Warning


When the thermostat valve does not open even when the engine is warm. Then the circle of coolant will not circulate throughout the engine coolant gallery. Due to which the temperature of the engine starts getting higher than the normal temperature in no time. Due to this, the temperature gauge in the cluster meter of the vehicle starts moving towards the red overheating indication.

And in some modern technology vehicles the high temperature light comes on in the digital cluster meter. This symptom is most common when the thermostat does not open, which should never be ignored. so that you can change the new one after inspecting the bad thermostat in time.

2. Unstable Temperature Gauge

When the thermostat valve of your vehicle’s engine coolant assembly becomes stuck due to corrosion, and the thermostat valve remains permanently open. It is then unable to stop the flow of coolant to reach normal engine temperature and the engine runs cold longer.

When this happens, the temperature gauge shows an engine temperature lower than normal and when the vehicle moves at high speed on the highway, then the cold air coming from the front comes directly to the radiator. and starts cooling the coolant more than normal temperature.

And the thermostat is unable to stop the hot coolant. Due to this, cold coolant starts circulating directly in the engine block and head gallery. Due to this, the engine does not reach its normal temperature. In this situation, when the vehicle is moving at high speed on the highway, the temperature gauge shows the temperature of the engine almost at the bottom (zero) level.

And when the vehicle is parked at a place with the engine started. Then the temperature gauge shows the engine temperature at a normal level. Thus, an unstable temperature gauge is also a main symptom of a bad thermostat. Never ignore it for long.

3. Cabin Heater Issues

You often use AC in your car during summer and heater during winter. In winter, a car’s heater provides heat only through the engine’s coolant temperature, because the flow of coolant from the engine runs in the heater coil and when the coolant gets hot, the heater coil heats up.

And the air from the blower fan passes through the heater coil and reaches the cabin of the car. But due to the bad thermostat valve being permanently open, the engine coolant does not get heated. Due to this, the heater does not run in the cabin of the car and the blower only blows cold air. The heater not running in the cabin of the car, that is, the blower blowing cold air even when the heater is on, is also a main symptom of a bad thermostat.

4. Coolant Leaking

The most common symptom of a bad or failing thermostat may be a leak of coolant. However, leaking coolant can also occur when other parts of the coolant assembly fail. But a bad thermostat causes the coolant to leak when it tries to reach the radiator. Then the closed thermostat blocks the coolant’s path. Due to which the flow of coolant increases. Then coolant starts leaking from the thermostat housing. When this happens, it is mandatory to inspect the vehicle.

5. Engine Overheating or Overcooling

A thermostat is a type of valve that opens or closes according to the temperature of the coolant. The thermostat valve remains closed when the coolant cools and when the coolant gets hot, the thermostat valve opens. But sometimes, due to the old age of the thermostat or due to corrosion, the valve of the thermostat gets stuck in the open or closed position.

When the thermostat valve is stuck in the open position. Then the engine runs overcooling for a long distance or for a long time and when the thermostat valve is stuck in the closed position. Then the engine runs with overheating.

6. Unusual Engine Sound

Vehicle engine overheating occurs due to a faulty thermostat or a valve stuck in the closed position, which causes a change in engine sound and performance. Due to this, the engine can cause vibrations and jerks. Along with this, there may be sounds of rumble, knock and rumble from the engine and the engine may stop suddenly, and with this, the hissing and bubbling sounds can be heard as the coolant boils.

Thermostat Replacement Cost

  • New Thermostat Cost – $30 To $$100
  • Mechanic Labor Cost – $$100 To $180
  • Total Thermostat Replacement Cost – $130 To $280

The replacement cost of the thermostat depends on the model of the vehicle and the quality and brand of the thermostat.

The cost of replacing the thermostat is not high. You can expect to pay the cost of a thermostat replacement from $130 to $280 by a professional auto mechanic. In which case the price of the thermostat unit can be between $30 and $100. However, for luxury and sports cars and other large vehicles, expect to pay a higher price for the thermostat.

And a mechanic may charge a labor charge of $100 to $180 to replace the thermostat. Because the labor cost of a professional auto mechanic can be as high as ($100 to $120 an hour, replacing the thermostat can take anywhere from 1 to 2 hours.

If you get the thermostat replaced by an independent mechanic’s, then you can get some relief in the mechanic’s labor charge. Because the mechanic labor cost of a certified mechanic garage is always higher than that of an independent mechanic.


Q. Can you drive with a bad thermostat?

No, it is recommended that you drive the vehicle for a long time with a faulty or stuck thermostat. because driving a vehicle with a faulty or stuck thermostat can result in engine overheating and cause you to stop your vehicle on the road. Due to this, you may have to bear the cost of expensive engine repairs.

Q. Can you drive a car without a thermostat?

However, some drivers temporarily remove a bad thermostat during the summer. But driving in any weather without a thermostat can be detrimental to the life of your engine. Because the engine cannot reach the operating temperature without a thermostat, due to which the performance of the engine may decrease.

Q. Is it difficult to replace a car thermostat?

If you do not have any experience replacing the thermostat, So, this task can be difficult for you. But replacing the thermostat is not such a difficult task for a professional auto mechanic. However, in some vehicles, it may be difficult to reach the fitting location of the thermostat.

Q. Where is the thermostat located?

The thermostat is located close to the water pump on the cylinder head in most cars’ engines. The top radiator hose lets coolant flow through the thermostat to the engine.

Share If You Like

Leave a Comment

error: Content is protected !!