5 Signs Your Car's Thermostat Is Bad (& How to Replace It)

The thermostat regulates the coolant flow into and out of the engine. A coolant temperature sensor displays the temperature on the dashboard.

A malfunctioning thermostat can cause your engine to overheat or not operate at the optimal temperature. This could lead to serious engine damage.

This article will explain the location and most commonly occurring symptoms of thermostat problems. It also explains how to replace a thermostat. Let’s begin with a quick look at the signs to look for.

5 Bad Thermostat Signs

A bad thermostat can lead to an overheating or unreachable operating temperature.

These symptoms will alert you to the need for precautions. This is a detailed listing of symptoms associated with a thermostat problem:

Overheating Engine

The hot coolant can't flow to radiators if the thermostat is closed. It is impossible to cool the hot fluid down and it causes the engine temperature to rise higher than normal.

To cool down, the coolant must make it to radiator. After this happens, coolant returns to the engine where it dissipates heat more efficiently. But, because of the thermostat that is stuck, coolant continues to stagnate, accumulating more heat.

Overheating can lead to serious engine damage. For example, if you end up with a blown head gasket, you are looking at massive repair bills.

However, an overheating engine isn’t always caused by a bad thermostat. Check the coolant levels regularly to make sure you have sufficient fluid. It could also be due to a bad water pump or a cooling system leak. The radiator may also become blocked. The thermostat is still an important part to inspect. 

Problems reaching Operating Temperature

The thermostat could be left open if the complaint was true. This allows coolant to freely flow to the radiator. The operating temperature may not reach its normal range if coolant is left in an engine for too long. It will struggle not only to heat up, but will also be unable to maintain its temperature range.

When the engine doesn’t get warm enough, it’s going to be less efficient. It is possible that your motor uses more fuel than normal, leading to increased costs at the pump. Premature wear can also occur in engine parts. 

Temperature Fluctuations

The thermostat can become unstable if it starts to malfunction. The thermostat could get stuck open where it is supposed to be shut and vice-versa. This malfunction leads to temperature fluctuations in the engine that aren’t normal. 

When the thermostat doesn’t fail uniformly, it can create mixed signals. Strange temperature readings can be noticed, which could lead you to question the cause. A quick inspection of your thermostat could reveal what is causing the issue. 

Fluctations with heat

Coolant warms the car heater. Therefore, you may experience temperature fluctuations inside the car from the vents if the thermostat is not doing its job properly to maintain an even temperature in the car’s engine.

It is time to inspect the thermostat if both the temperature and heat in the vehicle fluctuate.

Possible Leakages & Steam from engine

The thermostat may not be working correctly and the engine coolant chamber's hot coolant will escape from excessive pressure. As we all know, hot air rises. When water heats up it boils to form steam.

If the coolant gets hot and pressure is too high it can cause leaks. The radiator tank is frequently emptied of coolant.

Because they can be seen, leaks are easy to spot.

Rising Temperatures and Full Expansion Tank

The thermostat flap must be closed to prevent coolant from escaping the radiator. Coolant within the radiator heats and converts to steam.

If the temperature gauge is rising and your radiator tank has a lot of water, it could be a thermostat problem. The car could also be overheating if the coolant level is rising.

Poor Performance

The thermostat is an essential component that ensures the engine runs at its maximum temperature. Without it, the engine won’t operate as it should.

When the motor isn’t running right, you are going to notice performance issues. The engine will work harder to correct temperature differences, which is likely to lead to a decrease in fuel economy. 

There could also be higher emissions if the engine overheats or is unable to reach the temperature. Not only is the bad thermostat putting the engine at risk for failure, but it’s also contributing to a polluted environment. 

What Does the Car Thermostat Do?

The car thermostat’s job is to keep the engine’s temperature within its working limits. The thermostat is a small device that sits between radiator and engine, controlling coolant flow. When the thermostat closes, the coolant isn’t able to flow. When it’s open, coolant flows to dissipate heat. 

To ensure the best performance, most car engines built in the last few years have operated at the same temperatures. The engine temperature should generally be between 195 and 220 degrees Fahrenheit. When it doesn’t run within these temperature guidelines, it’s not operating efficiently. 

The engine heat rises quickly when coolant is not allowed to flow into the radiator. The radiator heats up quickly, on the other hand. 

As a gatekeeper, the car thermostat acts as an alarm system. It’s either allowing or blocking coolant from flowing from the motor into the vehicle’s radiator. It’s the job of the thermostat to read the temperature of the engine and determine if the coolant needs to flow or not. The thermostat will open if the temperature is high and allow the coolant to flow. The thermostat remains closed if the engine is cold. 

Locate the thermostat

The thermostat is often located in a plastic or metal housing near the water pump, connecting to the radiator’s lower hose.

It is most often located on the housing that connects the radiator’s lower hose, but it can be the upper hose in some cars.

It is almost impossible to locate your exact car model because it is usually installed within a housing.

Thermostat replacement cost

On average, the cost of replacing a thermostat is $70 to $450 depending on what model you have and how much labor it takes. The thermostat is about $20-$50, and labor costs at a workshop are between $50 and $400.

Many cars are equipped with an integrated thermostat housing that makes it hard to replace the thermostat on its own. The part can be very costly.

Some cars have a thermostat that is badly placed, which can require hours of labor. On other cars the thermostat can be replaced in ten minutes.

You can find the exact cost to replace your car's thermostat in a repair manual.

How to test a bad thermostat

It doesn’t take a lot of mechanical knowledge to test the car thermostat. You only need to do a visual check.

First, remove the radiator cap. It’s under the hood, near the front of the vehicle, mounted to the radiator. Don’t ever open the radiator cap when the engine is hot. You should not perform this test on a hot engine. The motor should start when the car is turned on. 

Coolant should not be flowing into the radiator when you examine the neck. The coolant should not flow inside the engine when it is cold. If you already see coolant running, the thermostat is open when it shouldn’t be. 

If the coolant isn’t flowing while the engine is cold, everything is running as it should so far. Allow the motor to warm up before you allow it to flow again. You should be cautious with hot coolant as it could cause injuries.

Coolant will flow into radiators as the temperature increases in motor. If you don’t see any coolant moving but the temperature is rising on the dashboard, the thermostat might be stuck closed. In either situation, you must

FAQ about thermostats