How Does A Car Thermostat Work? [Easy Guide]

The average human body sits approx 98.6°Fif it’s only a few degrees higher, it indicates something is wrong.

A car engine works in much the same way, on average between 195-220 °F. One of the main components in charge of regulating hot or cold temperatures is a thermostat.

How does a car thermostat work?

Simply put, it responds to changes in the temperature of the engine coolant. If it’s cold, the thermostat remains closed, keeping it in the engine.

If it gets too hot, the thermostat opens, allowing it to flow into the radiator where it will cool.

Still not sure?

Worry not, because in this guide, we’ll cover everything you need to know about automotive thermostats.

That includes what it is in general, how it works, and how to tell if it’s not operating properly. Finally, we will provide a step-by-step guide that explains how to check a car’s thermostat.

Let’s jump into it!

What is a Car Thermostat?

The thermostat is one of the main components of the engine cooling system, serves to regulate the flow of coolant between the radiator and the engine.

While it may be small in size (fits in the palm of your hand), the work it does is essential to keep your engine at a safe operating temperature.

Too much heat for too long, and you could end up with a cracked engine block or a cracked head gasket (basically both) worst case scenario).

How Does a Car Thermostat Work?

car thermostat

As coolant flows through the engine, it picks up excess heat. After leaving the engine, it goes to the radiator, where the excess heat is removed. Then make a few more stops along the way through the cooling system and end up back at the engine.

The thermostat is basically a valve between the engine and the radiator.

When the coolant in the engine gets too hot, this valve opens, allowing it to flow into the radiator where it will cool. If not heated, the thermostat remains closed, allowing coolant to continue circulating within the block.

How does the thermostat know when to open or close? It has features unique types of candles acting as an expansion agent. When the heat reaches a certain temperature, the agent expands, which opens the valve.

When the heat subsides, the agent shrinks, returning the valve to its normally closed position.

As you may have guessed, an engine running on a hot cooler won’t be able to cool down, meaning there’s a risk of overheating. Let’s now take a look at some of the most common signs that suggest your thermostat needs attention.

What Are the Symptoms of a Faulty Thermostat?

Poor Engine Performance

man in car driving through road

Imagine going on a long hike on a hot summer day only to find out that you didn’t bring any water with you. There’s no way you can continue for long.

This is also how it works for your car. If the thermostat is not working properly, the engine cannot cool itself. When this happens, you will notice a decrease in engine performance as it is difficult to keep up.

One of the more obvious signs that something in your cooling system isn’t working is a drop in fuel economy.

Engine Overheated/Not Hot

engine too hot

As one of the main devices in charge of controlling the temperature inside the engine, if the thermostat does not work, the gauge will end up outside the range it should be.

If the thermostat is stuck in the open position, the coolant will continue to flow. This can prevent the engine from reaching its optimal operating temperature, reducing things like engine power and fuel economy.

The other side of the equation is overheated engine, which can be a serious problem. This occurs when the thermostat is stuck closed, not allowing the hot coolant to cool in the radiator.

If this is left for too long, it can cause real damage to your machine.

While many things can cause an engine to overheat, a faulty thermostat is one of the first things you should check.

Machine Temperature Fluctuates

temperature warning light

Another symptom related to temperature is fluctuations in the gauge. If you frequently see it going from hot to cold (or vice versa), it may be because of a faulty thermostat.

If the thermostat does not open/close properly, the coolant escaping from the engine cannot be adjusted. This can confuse the system and cause it to display erroneous readings.

Coolant Leak

green coolant leak on the ground

Another sign that your thermostat is not working is if you see orange or green puddles of liquid under your car. When the valve does not allow fluid to flow out of the engine, it can damage the surrounding hoses, causing a leak.

If this symptom matches the other symptoms on this list, it may be time to check the thermostat.

How do you check a thermostat?

car thermostat

Fortunately, checking the thermostat is fairly easy.

First, start the engine and let it idle for a minute or two. After that, find and remove the radiator cap, and look inside to see if any coolant is flowing.

At this point, the engine shouldn’t be hot enough to require cooling, so it shouldn’t be flowing. If so, chances are the valve is stuck open.

Another possibility is that the valve is stuck closed.

To check, allow the engine to warm up slightly to its optimal operating temperature, then see if any coolant is flowing. Otherwise, it must match the rising temperature gauge indicated on the instrument panel.

Either scenario suggests you need a new thermostat. Depending on how smart you are under the hood, you may be able to change yourself between $50-$150. Otherwise, the store will handle it for you for between $200-$300.

With Small Size Comes Big Responsibility

Size aside, the thermostat in your car has an important job to do. If it doesn’t work as intended and you ignore the symptoms that suggest it, you’ll end up with a massive (which is important) repair bill.

Be a responsible car owner and take it take care of him all his life. This is without a doubt the best way to ensure it stays strong.

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