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Coolant Temp Sensor Bad? 4 Signs You Need to Watch Out For!

Coolant Temp Sensor Bad

The engine in your car gets very hot when you’re driving it around. In fact, it’s not uncommon at all for it to top the 200-degree mark in some instances. But if it weren’t for the coolant in your car and your coolant temp sensor, it would get even hotter than that! And it would overheat all the time and cause all kinds of problems for you.

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With this in mind, it’s important for you to make sure that you have enough coolant circulating through your car’s cooling system at all times. It’s also just as important for you to have a fully-functioning coolant temp sensor. If you don’t you could very well find yourself sitting behind the wheel of a car that is overheating on a regular basis.


Keep reading to find out more about what a coolant temp sensor and how you can tell if it’s gone bad. We’ll discuss what you can do to replace it and how much coolant temp sensor replacement will likely cost you.

What Is an Engine Coolant Temp Sensor and How Does It Work?

Your car has a bunch of different sensors located throughout it. There are more than a dozen located in the engine alone, including everything from the intake air temperature sensor and the mass air flow sensor to the oxygen sensor and the knock sensor. Today, we’re going to talk exclusively about the engine coolant temp sensor.


The engine coolant temp sensor is a sensor that is designed to keep track of the temperature of your coolant when you’re driving your car around. It’s often exposed to the flow of coolant in your car either in the engine block or in the engine cylinder head, though there are some times when it’s exposed in both areas. Either way, your coolant temp sensor’s job is to gauge the temperature of your car’s coolant and let your engine control unit know about it.


Once your coolant temp sensor lets your engine control unit know what the temperature of your coolant is, your engine control unit will then communicate with your engine temperature gauge about it. This gauge is then built to let you know if the coolant in your car is ever warmer than it should be. If it is, you’re going to want to stop using your car right away so that your engine doesn’t begin to overheat on you.

How Often Should an Engine Coolant Temp Sensor Be Replaced?

Generally speaking, you shouldn’t have to be too worried about your car’s coolant temp sensor dying on you. It’s a sensor that should last for well over 100,000 miles before you even have to think about having it replaced. But there are some instances in which your coolant temp sensor might give out on you much sooner than that.


Specifically, you can expect your coolant temp sensor to begin to go bad well before the 100,000-mile mark if you don’t make it your mission to maintain your car’s cooling system. If you have dirty coolant flowing through this system, it can cause corrosion to occur within your coolant temp sensor. This corrosion could knock your coolant temp sensor off course and make it impossible for it to keep tabs on the temperature of your coolant.


You’re going to need to keep your eyes peeled for problems with your coolant temp sensor since it could go bad on you at any moment. There are some signs that will show you that you need to replace your coolant temp sensor as soon as possible.

What Are the Signs of a Bad Engine Coolant Temp Sensor?

In the event that your coolant temp sensor ever goes bad on you, it shouldn’t take you too terribly long to tell. A malfunctioning coolant temp sensor is going to start sending bad information to your car’s computer, which is going to result in all kinds of issues. Here are some of the signs of a bad coolant temp sensor and what you should do about them.

1. Terrible Fuel Economy

If you have a bad coolant temp sensor in your car, one of the first things that you’re going to notice is that your car will suddenly start getting terrible gas mileage. This is going to happen because the signals that your coolant temp sensor sends to your car’s computer are going to throw off all of the different fuel calculations that are done in it.


In some cases, your car’s computer might even think that your engine is cold when the coolant temp sensor stops working. This is going to lead to it sending way more fuel in your engine’s direction than it should. You’re going to find yourself burning through fuel at a rapid pace and having to refill your fuel tank more often than usual.


You might be able to get away with driving around in a car that operates like this for a little while. But eventually, you’re going to find yourself wasting more and more money on gas. Your only option is going to be to have a mechanic take a look at your car to see if a bad coolant temp sensor is causing your poor fuel economy.

2. Black Smoke Coming Out of the Engine

You never (ever!) want to see any smoke coming from your car’s engine. But that’s exactly what you’re going to see in many cases when you have a bad coolant temp sensor in your car. The smoke coming out of your engine when your car has a bad coolant temp sensor will typically be black and sooty to some degree.


This black smoke will be an indication that the fuel mixture in your engine is entirely too rich. It’ll be so rich that your engine won’t be able to burn it in its combustion chamber, and that will result in black smoke. And it’ll all be caused by a bad coolant temp sensor that is feeding your car’s computer bad information!


Believe it or not, you can actually continue to drive a car with black smoke coming from the engine for a little while. Some people who own bigger trucks will do it all the time. But it’s not a good idea to keep on driving a car when you know that the black smoke is a result of a bad coolant temp sensor. You could face bigger issues down the line, which is why you’ll want to have a mechanic look at it.

3. Engine Overheating

A few moments ago, we mentioned how a bad coolant temp sensor might tell your car’s computer that your engine is always cold. We also talked about the problems that could result from that. But what about if your coolant temp sensor goes the other way and tells your car’s computer that your engine is always hot? That’s another thing that could happen with a bad coolant temp sensor!


If this turns out to be the case, your bad coolant temp sensor is eventually going to cause your engine to overheat. It’s going to overheat because your car’s computer will make the fuel mixture in the engine too lean. Outside of the fact that your engine will overheat, it might also start misfiring. It’s going to be a bad situation all around.


You shouldn’t ever drive your car if you notice that it’s overheating. Even though the overheating might be occurring simply because your coolant temp sensor is bad, it’ll still be overheating nonetheless. And you could do some serious damage to your engine if you drive around your car while it’s overheating.

4. Check Engine Light On

If there is a problem with any of the sensors in your car, you’re more than likely going to see the check engine light on your dashboard turn on. This light is going to signal that there is a problem with something under your hood (or in another part of your car!).


If you see the check engine light in your car come on, you should:

  • Take your car to your mechanic
  • Have your mechanic pull the codes from your car’s computer to see what the problem is
  • Replace your coolant temp sensor if it’s causing your check engine light to turn on

There is a good chance that you’re going to see more than just your check engine light come on when you have a bad coolant temp sensor. But it could very well be the first sign that you see when your coolant temp sensor is on its last legs.

Can You Drive a Car With a Bad Engine Coolant Temp Sensor?

If you suspect that you might have a coolant temp sensor that has gone bad, you may be tempted to continue driving it as long as the issues with your car don’t seem too bad. But this is pretty much always a bad idea since your car will constantly be on the brink of breaking down on you.


When you drive around in a car with a bad coolant temp sensor in it, you run the risk of:

  • Cylinder head gasket failure
  • Cylinder head warping
  • Engine block failure

You could also find yourself having to replace parts like an oxygen sensor when you insist on driving in a car with a bad coolant temp sensor. You’ll be much better off having your coolant temp sensor replaced as opposed to pushing it any further.

Who Can Replace an Engine Coolant Temp Sensor for You?

The good news for those who have a bad coolant temp sensor in their car is that replacing it shouldn’t be the most difficult job in the world. If you know your way around a car, you may be able to pull off coolant temp sensor replacement yourself. But you might also want to leave it up to your ASE-certified mechanic to do it.


To replace your coolant temp sensor, a mechanic will:

  • Release the pressure in your car’s cooling system
  • Find your bad coolant temp sensor
  • Remove the electrical connector for your coolant temp sensor
  • Take your bad coolant temp sensor out
  • Put your new coolant temp sensor in place
  • Fill your cooling system back up and test out the new coolant temp sensor

The labor associated with replacing a bad coolant temp sensor is minimal. It’s why it shouldn’t cost you too much money to have a mechanic do it.

How Much Does Engine Coolant Temp Sensor Replacement Cost?

When you consider what an important role your coolant temp sensor plays in the context of your car, you might be under the impression that it must cost a fortune to fix it when it goes bad. But it’s not going to cost much money at all to do coolant temp sensor replacement.


On average, you should only be looking at paying $125 to $150 to replace a bad coolant temp sensor. That includes $80 to $100 for parts and $40 to $50 for labor. All in all, that will be a fairly small price to pay to get your coolant temp sensor back up and running again.

Is Selling a Car With a Bad Engine Coolant Temp Sensor Possible?

Since replacing a bad coolant temp sensor is easy and inexpensive, you’ll probably just want to go ahead and replace it if yours ever fails. But if you have a really old car with lots of problems and you don’t want to pay to have a bad coolant temp sensor fixed, selling your car could be another option!


Cash Cars Buyer welcomes the opportunity to buy cars with bad coolant temp sensors and other parts that have gone bad. We won’t hold it against you when you come to us to buy your car. We’ll make you a strong offer for your car right after you provide us with some basic information about it, including:

  • The make and model of your car
  • The age of your car
  • The mileage on your car

We’ll also arrange to come and pick up your car from you at no added cost! So if you have a car with a bad coolant temp sensor and you don’t want to fix it, just contact us for more info on how you can sell your vehicle to us for top dollar.

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