Bad Thermostat Symptoms, Causes, and Replacement

The thermostat plays a crucial role in the car’s cooling system by controlling the flow of coolant into and out of the engine. Its main purpose is to ensure that the engine reaches its optimal operating temperature quickly. If the thermostat of your car is clogged or faulty, it may produce different signs, such as poor engine performance, to alert the driver. This article explains the bad thermostat symptoms, causes, and how to replace it.

Symptoms Of a Bad Car Thermostat

When the car thermostat goes bad, it produces different symptoms such as engine overheating, fluctuating engine temperature, heater not working, poor engine performance, coolant leaks, fuel expansion tank, strange noises from the engine bay, or poor fuel efficiency. 

Let’s discuss these symptoms of bad thermostat in detail:

1) Overheating Engine

car Overheating

An overheated engine is one of the first signs of a bad or stuck thermostat. When your vehicle’s thermostat remains closed, it prevents hot coolant from flowing to the radiator. As a result, the hot coolant will be unable to cool down the engine, causing the engine temperature to remain higher than usual.

For the coolant to be effectively cooled, it needs to flow through the radiator. When it goes through the radiator, the radiator cools it and returns to the engine, which helps to cool the engine. But if your thermostat is stuck closed, the coolant will not flow, leading to a continuous buildup of heat.

The overheating of the engine may result in severe damage. For instance, it may lead to a blown head gasket or a cracked cylinder block, which can result in significant repair expenses.

It’s important to note that your engine doesn’t always overheat due to a faulty thermostat. It’s crucial to inspect the coolant level to ensure an adequate amount of fluid is present in the system.

Other potential causes include a clogged radiator, a leak in the cooling system, or a malfunctioning water pump. Nonetheless, it is advisable to inspect the thermostat as one of the components to investigate.

Read More: Engine Overheating Symptoms and Causes

2) Trouble Reaching Operating Temperature

thermostat stuck open

If your thermostat is stuck open, the coolant will be allowed to flow continuously to the radiator. In such a scenario, the coolant does not spend enough time in the engine to reach and maintain the best operating temperature.

As a result, your engine will need to work hard to achieve its normal operating temperature and also will have difficulty maintaining the desired temperature range.

When your engine fails to warm up adequately, its efficiency is compromised. This can manifest in increased fuel consumption, causing extra expenses at the fuel pump. Furthermore, this issue may cause early failure of engine parts.

3) Heater Not Working

The proper functioning of your vehicle’s thermostat is crucial for maintaining a consistent temperature in the engine. It plays a role in heating up the coolant that is responsible for providing heat to the car’s heater.

heater not producing heat due to bad thermostat

When the thermostat fails to regulate the temperature effectively, it can result in temperature fluctuations from the vents inside the car.

If you notice fluctuations in both the temperature gauge on the dashboard and the heat output inside the car, it is a clear indication that the thermostat should be checked for potential issues.

4) Temperature Fluctuations

When a thermostat fails, it often leads to erratic and fluctuating behavior of the entire cooling system. Monitoring the temperature gauge on the dashboard can help identify spikes and drops in the needle, indicating potential temperature confusion caused by a faulty thermostat.

Overcooling is a famous sign of a faulty thermostat. This occurs when your thermostat is stuck open, preventing the engine from reaching its normal operating temperature. This issue can cause various problems as well.

5) Poor Engine Performance

The thermostat plays a vital role in maintaining the optimal temperature of the engine, and its proper functioning is crucial for the engine’s performance. Without a functioning thermostat, the engine will not work efficiently.

Loss in engine Performance

When the engine is not accelerating the vehicle properly, noticeable performance problems produce. One significant impact is reduced fuel economy, as the engine works harder to recompense for temperature inconsistencies.

A malfunctioning thermostat can result in the engine overheating or failing to reach the desired temperature. This can lead to increased emissions, contributing to environmental pollution in addition to putting the engine at risk of damage.

6) Coolant Leaks

Coolant Leaks, signs of bad thermostat

One of the major symptoms of a bad thermostat is the presence of coolant leakage. Typically, when your thermostat goes bad, it tends to get stuck in the closed position. This means that when coolant attempts to circulate through the radiator, the thermostat blocks its track.

In such a condition, your coolant starts to overflow, which ultimately starts to escape from the thermostat housing. This often leads to noticeable coolant leakage. It’s important to note that even if the thermostat is not the cause of the issue, it is still advisable to have your vehicle checked.

7) Full Expansion Tank and Increasing Temperature

When the thermostat valve is stuck closed, the coolant becomes trapped inside and starts to heat up, eventually converting into steam, while the coolant in the radiator doesn’t affect it.

car Temperature Gauge

If you observe the temperature gauge rising and notice your car’s radiator tank has sufficient water, it is highly likely that there is an issue with your thermostat. Additionally, an increasing coolant level can also indicate that the car is on the verge of overheating.

8) Strange Noises from the Engine Bay

Strange Noises from the Engine Bay

In addition to temperature-related problems, a failed thermostat can also cause peculiar noises from the engine bay. The gurgling, boiling, or knocking noises, may originate from the engine, radiator, or both. These unusual noises serve as additional indications of a failed thermostat and potential associated issues.

9) Poor Fuel Efficiency

Bad Fuel Economy

If your thermostat remains stuck open, the engine may run cooler than the planned limit. This may badly affect fuel combustion efficiency, resulting in poor fuel economy.

Read More: Causes of Low Oil Pressure

Causes of Bad Thermostat

The thermostat goes bad due to one or more of the following causes:

  • Contaminants
  • Poor Installation
  • Electrical Problems
  • Mechanical Failure
  • Coolant Contamination
  • Age and Wear

1) Contaminants

The contaminants such as minerals and corrosion may deposit inside your vehicle’s thermostat. These contaminants may badly affect the performance of your thermostat.

These contaminants usually accumulate due to insufficient maintenance or the use of poor-quality coolant.

2) Poor Installation

If your thermostat is installed incorrectly, it will be unable to work efficiently and lead to different problems. This usually happens if the gasket is not properly sealed, the thermostat is fitted backward, or the thermostat is not according to your vehicle’s manufacturer’s recommendations.

3) Electrical Problems

Few latest thermostats contain different electronic components that may stop working because of electrical issues. These components include the temperature sensor or the engine control module (ECM) that controls the working of the thermostat.

4) Mechanical Failure

Like other mechanical parts of your vehicle, the thermostat may also fail over time. It depends on a spring and valve mechanism. Over time, the spring or valve may be damaged, causing thermostat failure.

5) Coolant Contamination

A contaminated coolant is one of the major causes of a bad thermostat. If your vehicle’s coolant is contaminated with air bubbles, dirt, or debris, it may badly affect the functionality of the thermostat and lead it to work unevenly or fail.

6) Age and Wear

Over time, your thermostats may wear out due to normal usage and aging, like other mechanical components. The internal parts of your thermostat can weaken, leading to the poor performance of the thermostat.

What is a Thermostat?

The thermostat is a part of the car cooling system installed to control the flow of coolant through the engine and radiator. The thermostat is a temperature-sensitive valve located between the engine and the radiator.

bad Thermostat

The main function of a thermostat in a car’s engine is to ensure a minimum operating temperature. In the case of a cold engine, the thermostat doesn’t open and prevents coolant circulation through the radiator. This mode assists your vehicle’s engine to quickly reach its normal operating temperature, promoting efficient combustion and reducing wear.

Once the engine reaches a specified temperature, the thermostat opens up. This allows coolant circulation through the radiator, helping to regulate the engine’s temperature and keep it close to the thermostat’s rated temperature.

By restricting the flow of coolant to the radiator, the thermostat prevents rapid heat dissipation, which allows the engine temperature to increase quickly. Conversely, when coolant circulates through the radiator, heat is expelled rapidly, which helps the engine to cool down quickly.

In addition to its basic function, the thermostat also plays a role in regulating the engine’s temperature during extreme conditions. If your vehicle’s engine starts to overheat, the thermostat may open wider, increasing the flow of coolant and assisting in the cooling process.

Thermostat Location

The thermostat location varies according to vehicle make and model. The thermostat is commonly positioned within a housing made of plastic or metal, which is typically located near the water pump and connects to the lower hose of the radiator.

Thermostat Location

While it is commonly situated on the housing connected to the radiator’s lower hose, there are instances where it can be found on the upper hose, depending on the specific car model.

Due to its placement inside a housing, it is usually not visible to the naked eye and requires removal to be seen. In such cases, consulting a repair manual specific to your car model is a recommended approach to accurately locate the thermostat.

Thermostat Replacement Cost

The replacement cost of the thermostat depends on your vehicle model, labor cost, and the type of brand.

The average replacement cost of the thermostat is from $60 to $460. A thermostat costs around $30 to $60, and the labor costs from $30 and $400.

How to Test the Thermostat without removing it?

Follow the following steps to test your thermostat without removing it:

  • Turn on the engine of your car and let it idle.
  • Take a look through the radiator filler neck to observe the coolant flow.
  • Ideally, at this stage, the coolant shouldn’t be flowing since the car has not yet reached its operating temperature, causing the thermostat to remain closed.
  • If you notice that the coolant is indeed circulating, it indicates that your thermostat valve is open.

FAQ Section

What is the function of the thermostat?

The main function of a thermostat in a car’s engine is to ensure a minimum operating temperature. It performs this job by controlling the flow of coolant through the engine and radiator

What happens when a car thermostat goes bad? 

When the thermostat in your car malfunctions, it fails to accurately monitor the temperature of your engine, resulting in inadequate coolant flow to the engine. This may cause overheating and various associated issues, including coolant leaks and poor acceleration. If you notice signs of insufficient heating in your vehicle or random coolant leaks, it is advisable to have it professionally inspected. The culprit could potentially be a defective thermostat unit.

What would a bad car thermostat cause? 

A faulty car thermostat may have serious consequences, such as engine overheating, poor acceleration, or inadequate heating. Although these symptoms may not initially appear severe, they can ultimately cause expensive damage to the engine because of extreme heat. This damage may manifest as cracked components, seal breakages, or even engine blasts.

Can an engine run without a thermostat?

Driving a vehicle without a thermostat may lead to engine overheating. This occurs because the absence of a thermostat allows the coolant to flow through the engine too quickly, preventing it from adequately absorbing heat from the engine components.

What happens if the thermostat is removed?

If your car doesn’t contain a thermostat, it makes it challenging for your engine to maintain its optimal operating temperature. Consequently, the vehicle’s control unit continuously operates in a mode designed for cold starts, causing the engine to consume more fuel throughout its operation. This situation ultimately leads to a poor fuel economy.

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