How Does a Car Thermostat Work?

Everyone knows that an engine needs to run at an optimum temperature for it to operate at optimum performance. One...

Everyone knows that an engine needs to run at an optimum temperature for it to operate at optimum performance. One of the most important components that control an engine’s peak performance is the thermostat. This is an integral part of a car’s cooling system. It is sad that not many newbie vehicle owners know about this component. There are also seasoned drivers that know what it is, but don’t know how it works. This article will help you gain a better understanding of this component of your engine’s cooling system.

What is a Car Thermostat?

Modern car engines operate at a certain range of temperature for optimum performance. This can range between 195 degrees Fahrenheit and 220ºF. The thermostat helps the engine maintain its working temperatures within this range.

A car thermostat is a small device that sits between the radiator and the engine of a liquid-cooled car. Its principal function is to regulate the flow of engine coolant from the engine to the radiator. When closed, engine coolant cannot flow into the radiator which can lead to a rapid increase in engine temperature. When opened, engine coolant flows into the radiator where it dissipates heat and cools the now-hot coolant.

You can think of a car thermostat as a gate valve which allows or blocks the flow of coolant from the engine and into the radiator. This is dependent on the prevailing temperature of the engine. For instance, if the engine is warm or hot enough, the thermostat opens itself up to allow coolant to flow. If the engine is cold, the thermostat remains closed.

Thermostat

Car Thermostat in Relation to a Car’s Cooling System

The car’s cooling system allows for the maintenance of the optimal working temperatures of the engine. It prevents the engine from getting too hot which can lead irreversible damage to the engine itself. Coolant circulates through the engine and picks up excess heat. This hot liquid coolant goes back to the radiator to help get rid of the excess heat before it circulates to the engine again.

The car thermostat sits between the engine and the radiator. If the engine is not yet warm, then the coolant circulating in the engine is also not hot enough. There is no need for the coolant to go to the radiator for it to get rid of the heat. This is the main responsibility of the thermostat. It prevents the flow of coolant from the engine to the radiator, allowing the engine to reach its working temperatures a lot faster.

Once the engine reaches its operating temperature, the thermostat opens up to allow the flow of “hot” coolant into the radiator. This allows it to dissipate the heat and to bring down the temperature of the coolant. After this, the coolant recirculates to the engine.

Try to imagine an engine without a thermostat. Once you crank the engine, coolant already flows into the radiator. This keeps the fluid cool. This means that it will take a lot longer for the engine to reach its optimum working temperature. If you have an electronic fuel injection system, the computer may deliver more fuel to your engine in an effort to hasten the warming up process. This can translate to issues in fuel economy.

How Does it Work?

To put it in simple words, a car thermostat works by responding to the changes in the temperature of the engine coolant. If the engine coolant is cold, then the thermostat maintains its closed position. Once the engine coolant is hot enough, then the thermostat opens to allow the coolant to go to the radiator. It is a very simple yet very effective mechanism.

So how does the thermostat open and close?

The thermostat contains a cylinder filled with wax. This cylinder lies on the engine side of the thermostat so that it maintains contact with the coolant circulating in the engine. The cylinder also comes with a valve that connects to a rod. The rod presses into the wax at the center of the cylinder.

As the engine temperature rises, so does the temperature of the coolant. This slowly “melts” the wax. The “melting” wax expands which pushes the rod outwards. This outward movement of the rod is what opens the valve of the cylinder. Coolant can now flow from the engine to the radiator through this opening in the cylinder.

As such, when you start your engine early in the morning, the thermostat is still in its closed position. This allows the engine to warm up and reach its operating temperatures a lot faster. As soon as the engine is warm enough, the engine coolant also rises in temperature. This melts the wax and creates an opening for the coolant to flow.

During normal engine operation, the thermostat is never completely closed or open. Its state is dependent on the operating condition of the engine. Keep in mind that the thermostat serves like a gate valve controlling the flow of coolant from the engine to the radiator. This helps the engine to operate at the best possible temperature.

This can have substantial implications in engine performance. A well-functioning engine means the engine oil is able to lubricate all parts of the engine while also removing harmful deposits. This can also translate to a reduction in harmful emissions while also improving fuel economy.

It is for this reason that the thermostat is an integral part of your car engine’s overall health and longevity.

Automotive thermostat valve

How Do You Know You Have a Bad or Failing Car Thermostat?

Now we know what a car thermostat is and how it works. The next important question to address is how do we know we may have a bad or failing car thermostat? Here are some of the more common symptoms of a bad thermostat in your car.

  • Engine Overheating

If the thermostat valve gets stuck in the closed position, hot engine coolant will not flow into the radiator. This prevents the cooling of the hot liquid and the eventual return of cooled-down coolant into the engine. If you keep your engine running you run the risk of destroying it, quite literally.

Of course, engine overheating can also be due to other reasons. It could be because of a low coolant level or a failing water pump. It is also possible that there are leaks in the cooling system. The radiator can also develop clogs or leaks. While there are different reasons why your engine overheats, it is always best to include a bad or failing thermostat as one of the possible culprits.

  • Engine Underheating

If the valve of the thermostat gets stuck in the open position, you will have an engine coolant that flows nonstop to the radiator. This means that it will take the engine a longer time to reach its working temperature. It may also have difficulty maintaining it at the optimum range.

This can lead to a lower working efficiency of your engine oil which can hasten the speed at which engine parts wear down. It can also reduce the efficiency of the engine, leading to poor fuel economy. This can also translate to greater emissions over time.

  • Fluctuations in Engine Temperature

Engine temperature fluctuations are almost always an indication of a problem in the thermostat. It either closes or opens when it’s not supposed to. This occurs because the thermostat doesn’t get stuck in a single position. This leads to false temperature readings. Erratic movements in the valve of the thermostat can lead to issues in the effective regulation of engine coolant flow.

  • Poor Engine Performance

The thermostat allows the engine to operate at optimum working temperatures. If it is not functioning well, this can lead to problems in engine performance. One of the most obvious effects is poor fuel economy. Your engine will be hard-pressed to work with the inefficient cooling system.

How to Check Your Car’s Thermostat

Checking the condition of your car’s thermostat is easy. Open the hood of your car and remove the radiator cap. Start your car and allow the engine to run at idle.

Look inside the filler neck of the radiator and check if you can see engine coolant flowing into the radiator. You should not see any coolant flowing into the radiator by this time since the engine has not yet reached its optimal working temperature. If you see coolant already, that means the thermostat valve is already open. This may mean your thermostat valve is stuck in the open position.

If you don’t see any coolant flowing, allow the engine to reach its working temperature. As the engine warms up you should see coolant entering the radiator. If there is still no coolant flowing into the radiator and that temperature gauge in your dashboard is already rising, you may have a thermostat valve that’s stuck in the closed position.

In either case, you will need to replace your car’s thermostat.

A car’s thermostat is an important component of its cooling system. This can have substantial impact on the performance of the car’s engine.

Sources:

  1. 4 Symptoms of a Bad Car Thermostat – Do It Yourself
  2. Do I Need to Replace My Car Thermostat? – Axle Addict