Did you know that a bad car thermostat can damage your car’s engine? The engine will not operate within its ideal temperature range when the thermostat fails. Without a working thermostat, the engine would always lose heat to the radiator and take longer to warm up.
Keep reading to learn more about the signs of a bad thermostat.
What does a car thermostat do?
A car’s thermostat is the component in its cooling system that performs two main functions. First, it must get the engine to heat up to its optimum temperature as quickly as possible and then keep the engine at its optimum temperature.
The most popular type of thermostat regulates coolant flow to the air-cooled radiator. Such thermostats use a chamber that contains a wax pellet, which melts and expands at a set temperature.
This process operates a rod that opens a valve when the operating temperature is exceeded, allowing more coolant into the radiator. The composition of the wax determines the operating temperature.
In addition to monitoring temperature, the thermostat is also tasked with blocking coolant flow to the radiator when the engine temperature is cold. Until the engine is warm, the coolant will not flow through the engine when the engine is cold. As the temperature rises, however, the thermostat slowly begins to open.
When the engine reaches approximately 200 degrees Fahrenheit, the thermostat will be open entirely. As the opening allows hot coolant in the engine to flow through the radiator, the water pump pushes lower temperature coolant from the radiator to the engine.
By permitting the engine to warm up as quickly as possible, the thermostat aids in reducing engine wear and deposits and releasing unnecessary emissions.
Thermostats are successful because of their effective design. They are a small cylinder located on the engine side of the device, which is filled with wax that slowly melts at approximately 180 degrees F. However, this can vary greatly from vehicle to vehicle.
A rod connected to the center of the valve presses into the wax, and when the wax melts, it expands, pushing the rod out of the cylinder to open the valve and allow coolant to flow. The wax expands significantly because the wax is going from a solid to a liquid state. And it is expanding from the heat. When the engine is shut off, the process reverses to start again when the engine is restarted.
How does a car act when the thermostat is bad?
Here are the symptoms of a failing thermostat;
Unusual Temperature Readings
When you start up your vehicle after a long rest, you will usually notice that the temperature gauge starts from the cold side and eventually rise to the mid, which is the optimum engine temperature.
However, if there’s any malfunction with the thermostat, the coolant flow to the radiator will be affected. If the thermostat is stuck closed, the temperature will continue to rise dangerously. While if the thermostat is stuck open, the temperature will likely stop before reaching the mid-point.
Higher Cabin Temperature
Another common symptom of a failing temperature gauge is sudden temperature changes inside the vehicle. For example, if you notice that the temperature inside your cabin suddenly drops and then rises again, this can be a sure shot symptom of a failing thermostat that requires replacement.
Leaking Coolant
Coolant leakage is one of the most crucial signs of a failing or failed thermostat. This happens mostly due to a stuck thermostat. When the coolant tries to reach the radiator, the thermostat blocks its path leading to an overflow of coolant that escapes from the thermostat housing. When this happens, a major coolant leakage can be noticed. So even if the thermostat isn’t faulty, make sure to get your vehicle checked up.
Noises From the Engine Bay
If temperature changes weren’t enough, you would also experience strange noises within the engine bay. These strange noises can indicate a failed thermostat.
These noises can arise from within the radiator, the engine, or both. The strange noises may resemble a knocking, boiling, or gurgling sound as if something is boiling.
Heater Malfunction
If you live in colder environments, your thermostat will likely be stuck open rather than being stuck closed. This means that you will experience a heater malfunction rather than an overheat. Coolant will keep flowing to the engine even when it doesn’t need it.
Thus if you happen to live in colder climates or are driving in winters, make sure to check your heater. Even though problems with the thermostat are virtually impossible to avoid, a smarter step would be to replace a failing unit before it becomes a bigger pain.
Thermostat stuck closed symptoms
When the thermostat is stuck closed, the coolant’s circulation is blocked, preventing the coolant from getting to the radiator to be cooled. This will result in extremely hot engine temperatures, which will cause the vehicle to overheat.
An overheated engine can result in fast complete engine failure. Other broader symptoms that you might experience if you have a bad thermostat include;
- The temperature gauge reads lower or higher temperature than usual
- The vehicle’s head does not work
- Your automatic transmission cannot shift to higher gears due to the lack of power.
- Poor fuel economy.
- Temperature warning light illuminating the vehicle’s dashboard
- A failure in the head gasket
Thermostat stuck open symptoms
When the thermostat is stuck open, coolant flows into the radiator continuously, causing the engine to run cooler than recommended. Unfortunately, overcooled engines run inefficiently. Resulting in increased fuel consumption, higher emission levels, and an increase of wear on engine components.
Because the coolant flow is constant, and the engine’s temperature is not reaching its suitable level, the engine may exhibit performance problems. Additionally, the AC heater may not heat properly, as the heater uses engine coolant to produce heat.
If the thermostat is open all the time, then the coolant fluid will continuously pass through and go to the radiator. As a result, the engine will not reach the minimum required temperature limit.
In continuously cold engines, the oil will not lubricate the engine appropriately, which results in too much tear and wear and engine failure eventually. Besides, if the engine does not reach the required temperature, it will not provide the necessary power for the vehicle to move, especially at higher speeds.
How do you test a car thermostat?
You need to pull the thermostat out of your vehicle for this test.
Items needed;
- Kitchen pot
- A pair of needle-nose pliers
- A thermometer
Steps
- Put the kitchen pot on the stove filled with water to cover the thermostat.
- Place the thermostat in the pot without touching the bottom of it. Use a pair of needle-nose pliers for this.
- Start heating the water in the pot.
- When you see the thermostat valve starts opening, mark the temperature using a thermometer.
- Keep the thermostat in the pot while the temperature is rising.
- Measure the temperature again when the thermostat is fully opened
- Compare the two temperature values to the vehicle’s specifications. You can find the vehicle’s specifications in the vehicle’s service manual.
- The measured temperature should not differ significantly from the specified temperature in the vehicle’s manual.
- If the temperature is completely off the values given in the manual, you have a bad thermostat, and you need to replace it.
How to test car thermostat without removing it
First, you will need to locate the engine’s thermostat. If you open the vehicle’s hood, the thermostat housing is located at the end of the upper hose connecting the radiator to the engine. The actual thermostat is sitting inside the thermostat housing box.
When your thermostat is connected to your vehicle, there are two things you need to investigate:
- Check the coolant flow
- Open the radiator back.
- Start the engine and wait till it idles
- When you first start the engine, the coolant should not be flowing through the thermostat to the radiator.
- Simply because it did not reach the required temperature, if the coolant is flowing, this indicates a stuck-open thermostat. You can stop the test here.
- If the coolant was not flowing initially, and it did not flow when the engine got hot, this indicates a stuck-closed thermostat.
- Check the coolant temperature:
For this test, your hand monitors the temperature rise in the radiator hoses.
- Start when the vehicle is completely cooled down.
- Then fire up the engine and feel the temperature of the hoses. In the beginning, the temperature should be low, and they should feel hotter gradually.
- Make sure not to touch the engine when performing this test.
- Wait about 10 minutes and repeat the previous steps. If the hoses do not get hotter, the thermostat is stuck closed, and the coolant is not passing through to the radiator.
Note: Before performing any of the following tests, you need to make sure that the engine is completely cooled down. It is also recommended that you have a friend rev the engine and turn it off if it gets very hot.
What causes car thermostats to fail?
Here are the main reasons for thermostat failure;
Overheating
The thermostat senses the engine’s heat and then uses that heat to open and close a valve. If the engine overheats, this can cause the thermostat to fail. The components inside the thermostat are only designed to handle normal operating temperatures, and severe overheating may damage said components.
Sludge
Just as with any automotive fluid, the coolant can become contaminated and start failing over time. A common problem is the congealing of the coolant into thick sludge-like material.
his sludge can get inside the thermostat and cause the flow to be restricted or even cut off altogether. The sludge also prevents the thermostat from taking accurate readings, causing a delay in opening or closing, which leads to over-cooling or overheating.
Defect
Just like most automotive parts, the thermostat is mass-produced in a factory. Before a thermostat is released for sale, it is inspected for proper operation. Unfortunately, the human element plays a large part in inspecting the thermostats, and some problems are missed. These minor defects can lead to a thermostat being defective straight from the box or failing shortly after installation.
Age
Wear and tear are another common reason for failure. The thermostat is constantly heated and cooled, and after a while, the internal components can wear out. This usually occurs slowly and almost unnoticed, but the temperature at which the thermostat opens begins to get higher and higher until a complete overheating occurs one day.
Improper Installation
Installing a thermostat can be tricky at times, and even some professionals install them incorrectly. One common problem is to install the bleeder valve — commonly called the jiggle valve — upside-down, not allowing air to bleed from the cooling system.
Another improper installation problem is installing the thermostat backward. This puts the thermostat part that senses the temperature toward the radiator and not in the engine. The thermostat will still open and close, but it causes a long delay because the heat must travel farther before reaching the thermostat.
How often should you replace your car engine thermostat?
Car experts recommend car thermostat replacement after ten years. However, this is an optimistic number. Thermostats are more likely to stop working much earlier than a decade.
Some factors that induce an early thermostat failure include harsh weather, rough driving, and bad engine or thermostat parts. If the thermostat becomes faulty, you should either get it checked or replace it at the earliest.
Check this too: Symptoms of a Bad Radiator Fan
An unchecked failing thermostat can overheat the engine at a fast pace degrading the engine quality and efficiency. Therefore, it is necessary to set car maintenance schedules to extend the life span of car parts.