### What Does Your Car's Thermostat Do?

The thermostat regulates your vehicle’s engine temperature by adjusting the flow of engine coolant through the car’s engine. It does so via the wax thermostatic element which senses coolant temperature changes, expanding at high temperatures and contracting at cool temperatures.  

In other words, your thermostat is a vital part of your engine cooling system. Though it is not very common, a faulty thermostat can cause severe damage to your engine. Fortunately, a new thermostat is a rather inexpensive piece that can also be replaced relatively inexpensively, even with the labor costs involved.  

Hot coolant, a mixture of antifreeze and water, picks up heat through a running engine, causing the wax element to expand, placing the thermostat in the open position and allowing the coolant to be cooled by the radiator. Coolant circulating through an engine that is cool will cause the thermostat to remain in the closed position, helping the vehicle’s engine get up to normal operating temperature.  

Though not quite as bad as an overheating engine, an engine that is not able to achieve normal operating temperature because of a faulty thermostat is also a problem that should be addressed as soon as possible.    

Just mentioning your car’s thermostat to someone who does not know any better might make them think that it controls how warm or cold you can make your vehicle during the winter or summer. In fact, your vehicle’s thermostat is much more important than that. It helps regulate your vehicle’s engine temperature.  

Your car engine becomes extremely hot when in use because of the combustion occurring within  each combustion chamber. Your thermostat works to control the flow of coolant traveling through your car’s cooling system by opening and closing to prevent engine overheating or helping to get your engine up to normal operating temperature.  

### What is a Thermostat?

Your car’s thermostat is a small component that plays a large role in your car's cooling system. It is no longer than most adult fingers and looks like a peg with a spring surrounding it, a flat top, and a triangular bracket on top of that – almost like a miniature version of a vehicle’s suspension.  

Most vehicles’ thermostats are located within a thermostat housing near the top radiator hose on the engine block. Some vehicles’ thermostat housing is located on the lower radiator hose, though the majority of vehicles’ thermostat housing and top radiator hose are located near or between the cylinder head and water pump.  

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### Signs and Symptoms of a Bad Thermostat:  

Even though you cannot just pop your hood and look at your thermostat to see if something has gone wrong with it, there are several signs that could present themselves if your thermostat starts to malfunction. Luckily, faulty thermostats are relatively uncommon as they are simple components that do not require regular maintenance.  

__Check Engine Light or Temperature Gauge Readings:__
A check engine light that comes on can be terrifying for some, but for others, it is simply an inconvenience that many ignore. Both approaches are a little extreme since the check engine light can come on for a huge number of reasons. One of these reasons includes a bad thermostat, but this is usually from issues stemming from the faulty thermostat rather than a direct thermostat issue.  

Regardless of what the issue might be, getting your check engine light diagnosed should always be a priority as it can indicate anything from a loose gas cap to a misfire that can eventually lead to engine failure. As it relates to the thermostat, a check engine light can come on because of engine overheating, other cooling system issues like low coolant levels from leaks, or a coolant temperature sensor malfunction.  

A potentially better indicator of a bad thermostat is the temperature gauge. Though many new vehicles no longer have an engine temperature gauge, those that do will show you at what temperature your engine is currently operating.  

Some vehicles have an engine temperature indicator light rather than a gauge. It looks like a blue flag when the vehicle is not yet up to normal operating temperature, after which, it disappears. A red flag, a light that reads “TEMP”, or something similar will illuminate if engine overheating occurs.  

__Abnormal Engine Temperature Fluctuation:__
Normally, a vehicle that has been sitting for a while without running will be cold. As the engine warms up, you will be able to see the temperature gauge also rise. At normal operating temperature, the indicator will stop somewhere in the middle between the hottest and coldest ends of the dial.  

Noticing that the dial is showing erratic temperature changes can be a sign that there is an issue with your car’s thermostat or potentially with other components within the cooling system. Even if the check engine light does not illuminate, you should investigate the problem as a thermostat can be a minor component that causes major problems.  

Another potential cause of this, though also not that common, is temperature gauge failure or temperature sensor failure. You can check your thermostat to see if it is working or have a mechanic check the thermostat to verify which component is faulty.  

__Engine Overheating or Underheating:__ 
A more common faulty thermostat indicator is engine overheating or even underheating. A bad thermostat can get stuck in the open position or closed position, prohibiting or allowing the flow of coolant to the radiator at an improper time.  

If the thermostat is stuck open, the engine coolant will flow freely through the radiator hose and cool too much, not allowing the engine to reach normal operating temperature. If the thermostat is stuck closed, the engine coolant will not be able to flow to the radiator and thus, not allow the overly hot coolant to be cooled and recirculated back through the hot engine block.  

You will be able to observe consistent overheating or underheating on your temperature gauge or engine temperature warning lights.  

__Coolant Leaks:__
A thermostat that does not allow the proper flow of coolant to the radiator can cause coolant system leaks. There are a ton of hoses and components throughout your car’s engine. Components like gaskets, clamps, and the thermostat housing are weaker areas of the cooling system as they are connection points. The pressure caused by backed-up coolant causes these connection areas to leak more easily than solid hoses or parts.  

If there is a coolant leak, you will most likely be able to see a puddle of coolant on the floor underneath your vehicle.  

__Cabin Heater Failure:__ 
Since your vehicle uses the heat from its own engine to heat your cabin, the lack of heat when you turn it on can be an indicator of a faulty thermostat. There will probably be other signs of thermostat failure before the cabin heater fails or signs that accompany cabin heater failure, but cabin heater failure alone is not a great indicator of a bad thermostat.  

__Poor Engine Performance:__
Poor engine performance can be caused by many things. In this case, your engine performance will likely suffer because of the overheating caused by thermostat issues. Your car’s engine is happiest when it functions under normal parameters, but when your vehicle’s computer must start compensating for things that start taking it out of its comfort zone, performance can suffer in several different ways.  

You could see things like sluggish acceleration, an overall decrease in power, lower fuel economy, emissions system issues, a burning smell, unusual engine noises, and even visible steam coming from under the hood. Poor engine performance due to a faulty thermostat is usually a worst-case scenario type of situation.  

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### Testing and Replacing a Thermostat – Costs and Considerations: 

Thankfully, testing your vehicle for a faulty thermostat is quite easy. Replacing it is a bit more complicated, but it can be done quite easily depending on your vehicle. It can also be quite inexpensive, again, depending on what kind of vehicle you own.  

__Testing Your Thermostat:__
Before you go tearing off hoses and buying new components, it is always a good idea to make sure your thermostat is actually the problem. All you need to do is turn your car on, let it run for a minute, unscrew your radiator cap, and check to see what is happening. If the thermostat opens before the engine is warm, you will see coolant flowing to the radiator before the coolant temperature rises to appropriate levels.  

To check if it is stuck closed, let the engine run longer until it reaches normal operating temperature. If coolant is still not flowing, it is a good indicator that it is stuck in the closed position. If you witness one of these two conditions, you will need to replace your thermostat.  

It is best not to open the radiator cap when the car has been running as the cap and coolant can be quite hot and doing so increases the risk of injury. To check the thermostat’s condition, you will want to wait until the vehicle has cooled anyway.  

__Replacing Your Thermostat:__
You can replace the thermostat yourself to save some money in labor costs, but you should probably only do this if you want to learn how to work on your car a little more, if you are willing to be patient, you have a relatively simple car, or you know what you are doing.  

To replace the thermostat, you need to locate the thermostat housing, unbolt it, and remove the radiator hose from the housing at the other end for easier access. Once apart, you can remove the old or faulty thermostat and replace it with the new one.  

Make sure to have a catch can for any coolant that leaks from disconnecting the hoses. It is also a good idea to flush or at least replace the existing coolant in the system after you complete the thermostat replacement. Check the coolant level afterward to ensure that you do not cause any further problems down the road.  

Of course, the alternative option is to have a mechanic do the work for you. It will cost more, but it is the best route to go if you cannot or do not want to do the work yourself.  

### Thermostat Replacement Cost 

Thermostats themselves are not that expensive. They can range from $15 to upwards of $50 depending on how much is included. For something like a Honda, Hyundai, Chevrolet, Toyota, or Subaru, you can often just buy a thermostat.  

Automakers like Mercedes-Benz, BMW, and even some Nissans have thermostats that are integrated into a housing that includes a sensor or other components that drives up the cost. This can also be the case with many of the newest vehicles from any manufacturer.  

Labor costs can range from under $100 to $400 depending on the complexity of the thermostat, where it is located, and how much needs to be removed to get to it. Again, the most complicated vehicles with the most complicated parts will cost more.  

Overall, a thermostat replacement can cost anywhere between $20 and some of your own time if you replace it yourself to over $500 on the most complicated vehicles.  

You car's thermostat plays an essential role in keeping the engine running smoothly, by adjusting the amount of coolant it needs to stay at the proper temperature. We run down what it costs to fix, how to do it yourself, and signs of a bad thermostat here. 

My Car’s Thermostat – What Does It Do and Is It Easy to Fix?

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