What is a car thermostat?
The thermostat is central to your car’s engine cooling system. A car engine averages between 195-220°F, and the thermostat regulates the flow of coolant between the radiator and the engine.
The thermostat is small in size and roughly fits in the palm of your hand, but it plays an essential role in ensuring your car’s engine operates within a safe temperature range.
How does a car thermostat work?
As coolant flows through your car’s engine, it picks up excess heat, then, as it leaves the engine to travel to the radiator, the excess heat is removed. It makes a few more stops as it runs through the cooling system and eventually ends up back where it began: in the engine.
The thermostat is basically a valve that runs between the engine and the radiator.
When the coolant in the engine is too hot, this valve opens, allowing the coolant to pass to the radiator so it can be cooled.
If it is not heated, the thermostat stays closed, and this way the coolant continues circulating inside the block.
The thermostat knows when to open or close thanks to a unique wax that acts as an expanding agent. When the heat reaches a specific temperature, the agent in the wax expands, thus opening up the valve.
When the temperature lowers, the agent shrinks, and this closes the valve up.
An engine that’s running on hot coolant won’t be able to cool down, which puts your engine at risk of overheating.
This is why it’s essential you know what to look out for when it comes to a faulty thermostat.
Here are the most common symptoms…
Drop in Engine Performance
If your thermostat is not working properly, the engine has no way of cooling itself down. It’s basically the equivalent of you having no water on a boiling hot summer’s day.
When the engine can’t cool itself down, you may notice a drop in engine performance and fuel economy. These are usually the most obvious signs that something isn’t right with your cooling system.
Engine Overheating/Underheating
The thermostat is central to the controlling of the engine’s temperature, so if the thermostat is not working, the engine can easily underheat or overheat.
For example, if the thermostat is stuck in the open position, the coolant will continually flow. This prevents the engine from reaching its optimal operating temperature and will lead to a reduction in engine power and fuel economy.
On the other hand, if the thermostat is stuck closed, the coolant will not be able to cool down, and this can be an even bigger problem. If left untreated, it can cause long-term damage to your engine.
An overheated engine can be caused by several things, but one of the first things to check for is a faulty thermostat.
Fluctuating Engine Temperature
Another warning sign of a faulty thermostat is temperature fluctuations in the gauge, for example, if it goes from hot to cold (or vice-versa) frequently, it may be an indication that something is wrong.
If the thermostat is not opening or closing when required, the temperature of the coolant flowing in and out of the engine can’t be regulated. This easily confuses the system and causes it to display incorrect readings.
Coolant Leaks
If you see puddles of orange or green liquid under your car, it could be a sign that the thermostat is malfunctioning. This is because when the valve prevents fluid from flowing out of the engine, it can cause damage to the surrounding hoses, and subsequently causes them to leak.
You might notice this symptom along with several others on the list, in which case it’s definitely time to check the thermostat.
How to Check a Thermostat
So, you’ve noticed one or more of the above warning signs, and now you need to check the thermostat and determine what the problem is.
This is pretty straightforward, but if you’ve never checked a thermostat before, you might be wondering how to do this.
Here’s our guide for checking your thermostat:
- First, find and remove the radiator cap. The radiator looks like a narrow silver or black box and can be found at the front of your vehicle directly behind the grill. Look for the circular metal cap on the left or right side of the radiator and turn it counterclockwise to remove the cap. Bear in mind that if you’ve driven recently, you should wait until the engine cools completely before starting, otherwise, the test may be inaccurate. You should also refrain from opening the radiator cap immediately after running your vehicle, since it could be extremely hot and cause burns.
- Start your engine and let it idle for 10-20 minutes. You should leave your vehicle in park and turn it on so the engine starts – however, don’t run your vehicle in an enclosed space since it will create harmful fumes. From a cold start, your vehicle’s thermostat will stay closed and you won’t notice any coolant flowing into your radiator, therefore, you need to leave the vehicle running for about 10-20 minutes so it can reach its optimal running temperature. If you notice coolant flowing into the radiator straight after starting the engine, it means the thermostat is stuck in the open position.
- After 10-20 minutes pass, keep your head at least 1–2 feet (30–61 cm) away from the cap but look down into the radiator to check on the coolant. Usually, once the engine heats up, the thermostat should open up and this allows the coolant to flow through from the radiator to the engine. If you see the coolant flowing through the radiator, the gauge is open and your thermostat is working properly, if not, then it’s probably stuck closed.
- While your vehicle is still running, you should also check if the engine temperature gauge enters the red danger zone. If the engine temperature is in the red section of the gauge and the coolant isn’t flowing into the radiator, then the thermostat is likely to be the culprit. Most engines overheat when they exceed 220 °F (104 °C), however, this does depend on the make and model of your car.
Final Say
Whether your thermostat is stuck open or closed, either scenario suggests you need a new one.
Despite their small size, thermostats don’t come cheap, though your cheapest option is to replace it yourself (if you’re able to), which will cost you between $50-$150. If you’re not car-savvy, it’s best to leave it up to a professional, but this will set you back between $200-$300.
If you have an issue with your thermostat, it’s important to deal with this as soon as possible, as it plays a vital role in your car’s engine.
If the thermostat is not working as it should and you ignore the symptoms for too long, your repair bill is simply going to get bigger and bigger, so it’s best to nip the issue in the bud as soon as possible.