Home Diagnosis and TroubleshootingRadiators and Cooling System Bad Thermostat Symptoms – How To Go About A Replacement

Bad Thermostat Symptoms – How To Go About A Replacement

by Jordan Harris
Bad Thermostat Symptoms

Understanding the need for a thermostat and its functioning is crucial in helping you to identify bad thermostat symptoms.

A thermostat is the guardian angel of your engine. It always keeps an eye out for your engine’s temperature and cooling requirements. It monitors the flow of coolant through your engine, making sure you never suffer from engine overheating.

A thermostat is a straightforward device. It’s not in charge of any complicated tasks nor is it a complicated device itself. But in this case, the biggest problems can be caused by the smallest failures. A failed thermostat can be deadly to your engine, and if not treated promptly, it’ll affect your wallet as well.

What Is A thermostat?

A definition of a thermostat is “a device that automatically regulates temperature, or that activates a device when the temperature reaches a certain point“. The same role is played by the thermostat in your car and its main goal is to regulate the temperature of your engine.

In your car, the thermostat is a device that sits between the radiator and the engine in a car cooled by a liquid coolant. An open thermostat will allow the coolant to circulate through the engine. If the thermostat is closed, that means the path of the coolant to the engine is sealed off by the thermostat.

The decision on whether to be in an open state or closed state is made by the thermostat and depends on the temperature of the engine.

Modern cars need an engine temperature between 195ºF – 220ºF. And this temperature is required by the engine for it to attain peak performance. If the car’s engine is hotter than the engine temperature that the manufacturer desires, the coolant will flow through the engine until the engine gets to its optimal temperature. Similarly, if the engine is cold, the coolant will not flow and the heat produced by the engine will heat it up to optimal temperature.

Once the coolant starts to flow through the engine it is going to get heated as well. A hot coolant is not a coolant after all. For this reason, once the coolant has done its job with the engine, it is going to enter the radiator so that it can be cooled down to be used when needed again.

How Does A Thermostat Work?

A thermostat is an integral part of the car’s cooling system. The only way to fully understand it is by spending some time understanding how it works.

The car thermostat is a device that responds to the data it gets about the temperature of the engine. The coolant, once it flows through the engine block, will gain in temperature by heat transfer. By reading this data regarding the temperature of the coolant, the thermostat can find out the temperature of the engine.

Once the coolant is administered through the engine, if it’s cold, the coolant will circulate till it heats up. Thus, an engine is at its optimal temperature. If the coolant is too hot it will enter the radiator in an attempt to bring its temperature lower. A simple mechanism but highly effective.

How Does It Open And Close?

This action is what ultimately controls the flow of coolant in the engine.

A wax cylinder is equipped beside the engine. It’s fixed in the direction of the thermostat. This way, the wax will be in contact with the engine’s coolant and thermostat. The cylinder of wax is also pressed with a rod to its center.

When the temperature of the engine rises, so does the coolant. Since the coolant is in contact with the wax, it is going to increase the temperature of the wax as well.

The increased temperature is going to melt the wax. As the wax melts, the volume of the wax will increase as it expands. The expanded wax is going to push the rod outwards from the center.

Coolant Reservoir Empty

This movement from the rod is going to open the valve and the coolant is going to flow to the engine block. When the engine is cold enough, the wax is going to solidify again and the pressure pushing the rod outwards is going to decrease. This, eventually, will cease the flow of coolant into the engine.

Once you start the engine after long periods of inactivity, the coolant will not flow, allowing the engine to heat up and obtain its optimal temperature.

When the engine is operational, the thermostat will never be in a completely closed state. It will be open just enough to maintain optimal engine temperatures.

Bad Thermostat Symptoms

Now that you have understood and familiarized yourself with the mechanics and the function of the thermostat in your car, now you should be able to identify a malfunctioning thermostat. There are bad thermostat symptoms that, by being on the lookout for, you should be able to know when your thermostat is not functioning properly.

Engine Overheating

Engine overheating is the most common bad thermostat symptom. It makes sense since the main task the thermostat performs is maintaining the engine temperature. A bad thermostat will unquestionably be unable to maintain the engine’s heat and as a result, your engine will overheat.

The most common occurrence is the valve inside the thermostat is unable to open. It could be stuck, which would result in a closed thermostat. As long as it is stuck in a closed position, the coolant will not be able to flow to the engine which is going to result in your engine eventually overheating.

Another issue that could be haunting your thermostat is dislodged rod. The rod connected to the wax cylinder of your thermostat may be dislodged. When this happens, even though the wax solidifies, the rod is not going to return to its initial position. This is rare since the rod getting lodged in a position where it closes the valve is highly unlikely.

Change In Cabin Temperature

When you are inside the car and you set your AC to a particular temperature, you might be able to notice bad thermostat symptoms. What if the temperature inside your cabin is not stationary? Even though you set it to a certain temperature, it will continuously fluctuate.

This is another common sight with failed cooling and coolant-related issues. You might experience serious sudden chill spikes or you could feel like you are in the middle of a god damn desert. These temperature fluctuations are more probably not align with the temperature settings you’ve set for your AC either.

Cold Engine

Just like an overheated engine, the complete opposite is also a bad coolant symptom. When you start your engine, the engine is going to take much longer than usual to get to its optimal temperature.

Unlike the first scenario where your engine overheats because your thermostat is stuck in a closed position, this is the result of your engine getting stuck in an open position.

Even before your engine ever heats up, your thermostat is going to continuously send cooling liquid into the engine block. When your engine is continuously bombarded with chilling coolant, it is not going to be able to heat up for it to perform at its best.

This could also end up messing with your fuel economy as well. If you have an electric fuel pump or an electronically monitored fuel system, your car is going to pump much more fuel, thinking that the lack of fuel is what is not allowing the engine to heat up. Even though it pumps more fuel, the engine will not be able to heat up because of your cooling fluid constantly flowing between the engine. This would surely decrease your fuel economy.

Coolant Leak

When your thermostat is stuck shut, the coolant is going to build up behind the valve. This will increase the pressure of the coolant liquid stuck behind the valve. This would result in the coolant liquid leaking through small gaps of the thermostat housing.

Once owners see this, they mistake the coolant liquid on the floor to be the cause of the problem. But in fact, a problem with the thermostat eventually led it to leak coolant.

Check Engine Light On

With a bad coolant resulting in an overheated engine, it could cause the gasket to heat up. This is going to lead to your check engine light turning on or the temperature gauge spiking.

Once this is noticed, driving the car further could end up in a blown gasket. A blown gasket is never a good result, so it is best to park the car as soon as possible and avoid your car overheating further.

Check engine light might appear.

The check engine light could be a result of many other problems as well, but when it comes to a bad thermostat, there could be only a few options to take out of it.

You could be running low on coolant. It is possible that the coolant has leaked a bit too much and your car’s coolant system can no longer do its job resulting in a check engine light.

A bad radiator could also be the cause. If your radiator is clogged your coolant fluid will not be able to enter the radiator to cool down. If it is unable to get its temperature down it will not any longer be able to cool the engine.

A bad water pump could also be the cause. The water pump is responsible for pushing a mix of water and coolant through the radiator and the engine. When it goes bad, water and coolant can’t circulate through the cooling system, even if the thermostat is open.

Bad Heater

One of the bad thermostat symptoms could be that your heater is malfunctioning. When you are driving in cold weather, you would naturally try to pump up the heater. If you have a bad thermostat and it is constantly open, it could continuously cool down the engine and you will not be able to increase the cabin temperature even if you crank up the heater.

Rumbling Sounds

A bad thermostat will eventually result in rumbling sounds from the engine or radiator. Gurgling or knocking sounds might also be heard.

Though these sounds can not necessarily confirm that you are driving with a bad thermostat, the combination of any other bad thermostat symptoms will let you pinpoint the problems of a faulty thermostat.

Once you experience any of the following symptoms, ignoring them could cause much greater damage. It is advised to get your car checked at your earliest convenience if you ever come across any of the bad thermostat symptoms.

Effects Of A Damaged Thermostat

If you do not get your thermostat issue solved it could be a major hazard for your engine in the long run. At first, your engine will not be able to perform at its best capability.

Almost certainly with a bad thermostat, the check engine light is going to light up. If you notice that, it should be diagnosed immediately.

After a while of driving with a faulty thermostat, your car might start to stall regularly but eventually a long drive or just a hot day and you will end up with a blown gasket.

How Long Does A Thermostat Last?

A thermostat is going to be working whenever you start your car. And it is going to open and closed millions of times when you have used your car for a while. When considering this repeated motion of a thermostat, it is definitely going to bring up the question about the lifespan of a thermostat.

Even though a thermostat is going to go through this kind of motion constantly, generally it is not going to break regularly. Thermostat failures do not happen that often but it is not unheard of either.

It’s hard to put a number on how many years it is going to last but usually, it is going to work fine for about 10 years. Unless you suspect a failure with the thermostat, there is no reason to change it. If you are doing a major repair with your car’s cooling system, it is a good idea to swap out your thermostat if you think it has seen better days.

Thermostat Replacement Cost

Once you spot bad thermostat symptoms, you must think about getting one replaced.

Just like anything else, there is no standard price for a thermostat replacement. Different cars are going to require different thermostat models, and each one is going to be priced differently. But it is possible to get an average cost on thermostat replacement.

Labor cost is going to be different depending on where you reside. In some areas, the charge of a mechanic can be much higher relative to some other areas. Often labor costs are going to be between $70 to $150 per hour. This averages close to $90 per hour.

Price Of The Thermostat

The thermostat is cheap considering the vital role it plays in keeping the engine operational. A factory-made thermostat is going to vary in cost anywhere between $12 to 70$ for most modern cars, although supercars require high-quality thermostats.

But if you are looking for a cheaper replacement and do not necessarily require an original component, you could get it for somewhere close to half the price of the original factory-made thermostat.

Other than this, coolant must be replaced as well. The coolant is not gonna blow a hole through your wallet, at least. Generally, a good quality coolant is going to cost in the neighborhood of around $20.

Labor Cost

Labor costs are what is going to get you when considering a thermostat replacement. Different models require a different amount of time for disassembly and installation.

Most cars will require 1 to 2 hours to remove the existing thermostat and install a new one. In this case, you will be paying $100 to $200 for labor. But there are exceptions.

Some models like the older versions of the Volkswagon Passat have their thermostat placed behind the timing cover. So, replacing the thermostat in cars with a similar build will require disassembling the timing belt as well. This going to take a long time, as well as higher labor and cost. Removing the timing belt and reinstalling it will take somewhere close to 5 hours. And will cost around $500.

Once you analyzed bad thermostat symptoms and confirmed that your thermostat is busted, it is important to get it replaced, even though it might seem costly. If left unchecked, a bad thermostat will cause much bigger problems that would require a complete engine rebuild which will cost much higher. In some cases, it’s cheaper to discard your car.

Is It Possible Replace Thermostat Yourself?

Now that bad thermostat symptoms are spotted, why not get handy and fix it yourself.

Is it possible to replace a thermostat without paying a visit to the workshop? Yes, it is certainly possible. It is not going to be easy, and experience would certainly help. But fear not, as this step-by-step guide would make things easier if you decide to do this project.

First off, you will need some tools that you will be working with. It is best not to start with the procedure if you do not own or have the required tools at the moment.

Tools Needed

The tools required aren’t rare tools that people barely come across. These are available in most households and especially among car owners.

  • A wrench
  • A socket set
  • Screwdriver
  • Plastic gasket scrapper
  • Pliers

Other than these, have a new thermostat purchased and within reach so that once the current thermostat is removed, installation of the new thermostat can begin as soon as possible. Also, a drain pan will be required to drain the existing coolant.

Replacement Guide

So let’s get started, shall we?

Removing Existing Thermostat

  1.  Park your car in a safe place. Best to be at home in your garage. Or, any other comfortable place will do the trick. Make sure to have your handbrake engaged.
  2. Allow your car to cool down if you were taking a drive recently. Working with a hot engine could get messy and dangerous real quick. That’s especially if your thermostat is malfunctioning, so let your car rest and cool down.
  3. Removing the battery and cables is the next step. This is a safety procedure because, during the job, an exposed wire can easily shock you. If your car requires to be reprogrammed once the battery is removed, this is not going to be necessary, so just work your way around it.
  4. You can start working on the thermostat now. Once you pop off the thermostat cap, the existing coolant is going to spill out, so place a drain pan under it and pop off the thermostat.
  5. Locate your thermostat housing by making your way along with the radiator hose. Different cars have their thermostat in different places so there is no guarantee that you will find your thermostat housing at the end of the radiator hose. It is best if you are familiar with your own car.
  6. Now, you can get started on removing the thermostat housing. You can pop bolts off the thermostat housing. You will probably find 10mm or 12mm bolts find the right sockets and get started.
  7. Now that the broken thermostat is exposed, you can pull it right out. Some might be easy and some won’t budge. Put some muscle behind it and it will come out.

And now that the faulty thermostat is taken out of your car, all that remains is for you to fit the new one.

Installing New Thermostat

  1. You will definitely find some debris and rust on the mounting surface. To ensure a proper fit for the new thermostat, make sure to clean all the impurities before proceeding forward.
  2. The same way the old one came off is the way the new one goes in. So just like you removed one earlier, go about fixing this.
  3. Tighten the bolts of your thermostat housing. Locating it won’t be a problem this time
  4. Now, top off your coolant reservoir, and you are done.

That’s it, and you have saved a few bucks. But the joy of getting something done and the sentimental value is one that you can’t put a price on. Be sure to double-check whether all the bolts are fastened properly before concluding the work.

A bad thermostat can be a pain. Knowing how to spot bad thermostat symptoms and possibly replace one yourself will come in handy someday.

Car Thermostat Problems Facts:

  1. The thermostat in a car is responsible for releasing coolant into the engine when it becomes too hot.
  2. After about 10 years, the thermostat can start to go bad.
  3. Odd temperature gauge readings that are lower or higher than normal could indicate a problem with the thermostat.
  4. If the car is overheating all the time, it could be a sign that the thermostat is not releasing coolant into the engine.
  5. A malfunctioning thermostat can cause erratic and sudden air temperature changes in the car.
  6. Coolant leaking from the engine could be a sign that the thermostat has gone bad or that there are issues with the radiator hoses, radiator, or seals and gaskets.
  7. Strange sounds, such as rumbling, boiling, knocking, or gurgling, could indicate a problem with the cooling system caused by a bad thermostat.
  8. A thermostat stuck in the open position can prevent hot air from blowing through the car’s vents.
  9. If you notice problems with your heater, it’s a good idea to have your vehicle inspected for thermostat issues.
  10. It’s important to have your vehicle inspected if you experience any of these signs of a malfunctioning thermostat to prevent further damage to your car’s engine.

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