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Five Signs That Your Car Has a Bad Heater Core

Wrench Wench has been in love with automotive mechanics for decades. She loves sharing advice with fellow DIY mechs and curious cats.

You might experience only a few of these symptoms, or you might experience all of them at once. A lot of this depends on your vehicle, its age, and its health at the time when your heater core goes bad.

You might be wondering what the heck a heater core is, what it does, and how it can affect your vehicle. These are all great questions, and we’re going to get you some quick and easy answers so that you can get your car fixed ASAP.

Signs That Your Car Has a Bad Heater Core

  1. It's foggy in your car.
  2. Your car smells odd.
  3. Your car is devouring coolant.
  4. You have a chilly passenger compartment.
  5. Your car's cabin is cold, but its engine is hot.

More Questions Covered in This Article

  • What is a heater core?
  • What does a heater core do?
  • Where is the heater core located?
  • How do you change a heater core?
  • Can you drive with a bad heater core?
  • Can a bad heater core cause overheating?
  • How do I stop my heater core from leaking?
  • How can you tell if you have a blown head gasket?

This article will also explore the most common questions sent in by fellow readers in the "troubleshooting" section towards the bottom. If you have more questions as you read, make sure you scroll all the way to the end (another reader has likely had the same question).

1. It's Foggy in Your Car.

Is it foggy in here? The most common tipoff to a problem with a heater core is when the inside of your car suddenly fogs up for no reason. And, when I say "fogs up," I'm not talking about a little mist on the edge of the windshield, I'm saying every window is covered with moist, warm condensation.

What may have happened is that your heater core blew while you were driving, after the engine warmed up. The warm coolant leaking into the cabin of the vehicle caused fog because that coolant was previously sitting inside a warm and temperature-regulated coolant system, and now it's evaporating into steam as it hits the cooler air inside your car.

2. Your Car Smells Odd.

Do you smell melons? Whether or not the car got all foggy when the heater core broke, an unmistakable sign of a leaking heater is a fruity, sickly-sweet smell inside the car. This is the smell of your radiator fluid and definitely a sign that coolant is leaking into your car.

You might also smell this lovely smell around the outside of your car, which means it's time to look underneath your vehicle and see how much of that coolant has spilled out onto the ground.

3. Your Car Is Devouring Coolant.

Is your car rather thirsty? If you find your car, truck, or van has suddenly developed a voracious appetite for coolant, and you cannot figure out where it's all going, you may well be looking at a blown heater core. Sadly, if the leak is hard to find, the reason may be that the coolant has been leaking into your cabin when the system is cold, and instead of making fog it's creating a puddle. The first place I usually check to confirm a bad heater core is the passenger-side floor. If it is soaking wet, and so are any forgotten shoes or fast-food bags lying around down there, then I know to suspect the heater core.

4. You Have a Chilly Passenger Compartment.

Brrr! It's cold in here! A chilly passenger compartment is not always a sign of a faulty heater core. It may indicate that your blower motor or another component of your heater has gone bad (cheer up, it may be a component that’s less tedious to fix than the heater core). Though, if you're seeing one of the other signs in addition to a lack of heat that's a pretty good indicator that the heater core itself has a problem.

When a hole or puncture develops in your heater core, all that warm air may escape too quickly to reach you at the other end of the heater ducts. Depending on the size of the puncture, you might feel mildly warm, lukewarm, or absolutely freezing air coming from your heater.

5. Your Car's Cabin Is Cold, but Its Engine Is Hot.

Do you have a cold cabin and a hot engine? If you find that your vehicle has overheated, or continues to overheat, you'll want to check on the health of your heater core for sure. Bear in mind though, that many other parts of the car could be involved in the overheating. If your heater stops putting out heat, and your engine seems warm, investigate whether there is a coolant leak elsewhere, or some other issue with your car.

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Read More from AxleAddict

Overheating is very serious for your car. All sorts of major components of your car will wear and break down in record speed when they get too hot. If your car overheats, investigate the problem and get it fixed ASAP. If the temperature gauge goes up into the danger zone, don’t drive it; tow it. You don't have to heed my words, but I can guarantee you'll learn a hard lesson if you don't.

What Is a Heater Core?

It’s part of the car’s cooling system. It looks exactly like the mini-me version of your radiator, and is, in fact, a small radiator itself, with a grid of little tubes and a waffled appearance from the fins that disperse the heat. Your heater core allows your heater and defroster to function.

What Does a Heater Core Do?

Your heater core circulates coolant through the little tubes; the coolant comes in through one heater hose and out the other, radiating heat into your cabin so you don’t freeze on those cold winter mornings. It's also responsible for allowing your defroster to function properly, and it's linked into the air conditioning system, which is organized around similar principles.

Where Is the Heater Core Located?

Your heater core is usually behind your dashboard, under the center or the passenger side. It will have some sort of casing or housing and is usually buried behind almost every other component of the dashboard.

How Do You Change a Heater Core?

This job is way easier to describe than it is to perform. Often, a DIY'er will check out a Chilton's Manual or other auto guide and say, "No problem! I can change a heater core!"

I'm all for this kind of enthusiasm; it's how I myself got into changing heater cores. Though, let me forewarn you that it is a very tedious task, and once you know how to do it, all your friends and family will want you to change theirs too!

With that warning out of the way, I'm only going to give you a very basic guide for most cars and trucks from 1958 to 2010. For the details for your particular vehicle, you'll need to do your own digging.

Steps Required to Change Your Heater Core

  1. Disconnect the battery.
  2. Remove the steering wheel from the vehicle.
  3. Remove any outer doors or casings from things like the fuse box, speakers. and kick panels.
  4. Remove the glove box, radio, speakers, and any accessories.
  5. Remove any gauges (be careful if you have a speedometer cable back there!).
  6. Detach and remove your heater and air conditioner controls.
  7. Unbolt and remove the dashboard.
  8. Do not disconnect your air conditioning unless it's absolutely necessary and only if you have the proper means to dispose of the Freon. Do not just let it leak into the air. It is bad for the ozone layer and is toxic, especially to people with heart conditions.
  9. Disconnect the two heater hoses from the engine compartment.
  10. Move any air ducts or other components away from the heater core housing.
  11. Remove the heater core housing and set it on a table. Remove any screws or fasteners to gain access to the heater core.
  12. Take the old core out and put a new one in!

Note: To install your heater core, just follow these instructions in reverse. If anything got broken on the way out, please make sure to replace it on the way in.

Caution: As with most DIY tasks, you take on this one along with all the risks involved. These instructions are very basic and meant for a person who is already very mechanically inclined. If you don't have appropriate tools, safety knowledge, and a strong mechanical aptitude, you'll want to seriously consider taking your vehicle to a garage to be fixed by a professional.

Can You Drive With a Bad Heater Core?

A heater core often goes bad due to leaking. As the heater core uses engine coolant to generate heat, a leaking heater core will reduce the amount of coolant in the cooling system. Low coolant will cause an engine to run at a higher temperature, which can result in extensive engine damage.

Can a Bad Heater Core Cause Overheating?

Leaks are the #1 reason a vehicle begins to overheat. Leaks in hoses, the radiator, water pump, thermostat housing, heater core, head gasket, freeze plugs and a few other things can all lead to problems with the vehicle's cooling system. A small leak can quickly turn in to an expensive repair and a serious headache. Often times, the problem could relate to a blown gasket

How Do I Stop My Heater Core From Leaking?

If it is only a small leak in the heater core, most would recommend simply sealing that leak and leaving your heater core in place. You can do this simply by adding some gasket sealer to your vehicle's radiator when your vehicle is cold.

How Can You Tell if You Have a Blown Head Gasket?

There are some makes or models of cars that have a reputation for blowing head gaskets. One such vehicle has such a bad reputation for head gasket problems there is a group of owners trying to get the manufacturer to have a recall on them. If you happen to own one of these vehicles, don’t worry it does not mean that you have a bad car or that you are going to spend lots of money.

How To Tell if a Head Gasket Is Blown:

  • Coolant leaking externally from below the exhaust manifold.
  • White smoke from the exhaust pipe.
  • Bubbles in the radiator or coolant overflow tank.
  • Overheating engine.
  • White milky oil.
  • Fouled spark plugs.
  • Low cooling system integrity.

Question: Is It Possible to Have a Broken Heater Core and Not Exhibit Each of the Signs?

I own a 2005 Honda Civic. Lately, my a/c has been on and off. It runs Lukewarm and, as I gain speed, it gets colder. My passenger side floor has been thoroughly soaked, but not recently. However, I have not had any problems with coolant being low. No overheating. I'm certainly not a mechanic. I get in and drive. If it needs gas I fill it up. If it needs oil, I get it changed. That about sums it up. Is it possible to have a broken heater core and not exhibit each of the signs?

Answer: Yes! It's Definitely Possible

There are plenty of times when heater cores will go bottom up, and only barely exhibit one or two symptoms. In 90% of cases, you're going to clearly experience at least two or three signs that give away the culprit.

In your particular situation, especially without any loss of coolant, while I wouldn't rule out a bad heater core, I would look first towards your air conditioning unit. While it's not unusual for an aging vehicle to take a little time to blow out crisp and cold air, if your a/c is on the fritz, it could also be the culprit soaking your passenger side floor. Alternatively, you could also have a leak in the seals around your door, windshield or firewall—all of which could be soaking the floor as well.

Question: Still Smelling Coolant, Is This Normal?

Just bought a 2008 Chevy equinox. That same day I could smell antifreeze while the heat was running, so I took it right back and they said bad heater core. I got it back today, heat works great! However, I can still smell a very slight scent of antifreeze. Not like before, and it even seems to lessen as I drive, but when I restart it, I smell it again (slightly). Could this just be normal after having one fixed? Maybe there's a residue in the vents or something? I'm hoping it just goes away after a day or so. What's your opinion?

Answer: Yes... and No...

Yes, it's not unusual to smell a bit of residual coolant drying up in the system.

That being said, it's not normal for this smell to persist for more than a few days of driving. So, in greater detail to your individual plight, since you are describing a chronic type persistence in this smell, I would urge you to take your chevy back to the mechanic and have them check for any small leaks in your coolant system. While it could just be some residual coolant, it's more likely that there is a small leak somewhere that wasn't caught originally, or that occurred after your last heater core was replaced. It's not unheard of for this to happen, especially if your vehicle overheated or if there was any serious pressure in the coolant system when the heater core went bad.

Question: How Much Does Repair of the Heater Core Cost?

I am positive I have a heater core problem. Ironically, it started the day I got my car back from getting a fuel pump relay repaired. After paying a lot for the fuel pump relay, how much does repair of the heater core cost?

Answer: The Ballpark Price of Heater Core Replacement

This is a difficult question to answer, because it depends on what country and/or state you live in, what type of mechanic you see, and what type of vehicle you drive.

That being said, I can offer a ballpark idea of what I might charge and what common prices are found in my area (Seattle, Wa).

For me, a heater core is often a large job, not because it's difficult, but because in nearly all vehicles, the heater core is behind the dashboard. So, unless I have direct experience with a particular year, make, and model that I've performed this on, my initial assumption is that it will take no less than eight hours to disassemble the dashboard, retrieve and replace the heater core, and then reassemble the dash around it again. This is a general time estimate, including most newer cars that usually have lots of delicate electrical elements, clips and knucklebangers. As a mobile mechanic, my usual going labor rate was $60 an hour. So a general estimate for a heater core would be around $480.

Now, shops in the area, who often have more specialized tools, lifts, and predictable work environments, can often get the job done in half the time. That said, because they are running a business, their shop rates are going to be higher—$90 to $150 average. So for a 4-6 hour job in a shop, you're looking at a minimum of $360 to $600, plus the price of their preferred manufacturers heater core.

Question: Where's That Leak Coming From?

I own a 96 chevy corsica four cylinder. Two days ago, on my way back from work, I smelled a very sweet humid icky smell (coolant) inside my car. I kept driving only to see that white smoke started coming from my vents and my car started rapidly overheating. I pulled over to let the car cool about six times on the way home. When I got home, I looked under the hood and saw that all of my coolant was gone, after just getting it filled two weeks earlier. I asked around and everyone kept telling me that it was my heater core. Everyone also kept telling me to look for the missing coolant on my passenger side floor. It's still dry. I jacked up my car to find a leak and poured a gallon of water into the coolant compartment to do just that and I quickly jumped under the car. What I found was that all of the water was pouring out thru a one inch pipe connected to absolutely nothing right underneath the heater core. However, there was no leakage from the actual core itself. I was wondering if you could tell me if that is still a heater core problem or something else before I start tearing my dash apart? Please and thank you.

Answer: Pipes to Nowhere...

Okay, I first have to thank you for sharing this complication. To tell you the truth, without being able to stick my head under your hood, it's a little bit difficult to narrow down what you're seeing precisely. That being said, from your information, I would suggest that it's likely that your disconnected "pipe" either used to be connected to your heater core as a part of the inlet hose.

Your heater core is a really basic set up. You have your main radiator in the front of the car and two hoses (it's not often that they are pipes, but it's not unheard of), an inlet and an outlet, that connect to the corresponding pipes attached to the heater core. These pipes will often protrude from the fire wall, which is where I suspect you're seeing this "pipe to nowhere."

Question: What Are the Symptoms Before the Heater Core Goes Bad?

My mom's car just got repaired. Either the radiator or the fan kept turning off. Now, every time we turn the heater on in the car, it will be warm, but I can smell something sweet, like syrup, almost. I was worried about it, but someone told me that it wasn't the heater core because it won't give you any warning before it causes damage. They said that the mechanics probably just accidentally spilled some antifreeze. I really don't know what to think.

Answer: Bye Bye Heater Core...

I have to say, while I'm sure they meant well, it's sure naughty of your friends to assume that a+b always equals c, when it comes to cars. I'm no master mechanic, but out of everything I've learned, and that all other mechanics I know have learned, it's that vehicles don't always act the way they are supposed to. In fact, I'd imagine that 90% of professional repairs could be handled by any old monkey with a wrench, if it weren't for the fact that cars and trucks get old. Sometimes they are straight up text book, sometimes they do something completely bizarre and unexplainable, and you find out that it's something super easy and right in front of your face.

When it comes to heater cores, it's extremely common for them to leak out into your passenger compartment, because they are usually right up underneath the dashboard inside your car. Though the leak could be from somewhere else, such as the inlet or outlet hoses, where they would spill out onto the ground. If that happened, you wouldn't have your passenger floor soaked.

The same thing could be said about heater core's just "dying" without any warning. That is very common, though it's not because there are not any signs before hand, it's because most of us are too busy driving to notice the signs unless they stick out. So, smelling coolant, could definitely be a sign that your heater core has a slow leak and may need to be replaced soon. That being said, it doesn't mean that it is your heater core. If it were me, I would use a coolant leak checking tool, or take it to a shop and have them use one. In the first day or two after having a radiator changed, it would be expected to smell a little bit of drying coolant, but a chronic smell every time you turn the heater on, shows there is definitely something worth checking out; before something just dies on you without warning.

Question: Foggy Windows

I have an '01 Malibu. I've replaced the thermostat and the heater core, thinking that would stop my car windows from fogging up, but even after those repairs, my windows are still fogging up. What's wrong?

Answer: Check Things Out

Without knowing more, my initial suggestion would be to have your new heater core and thermostat checked out. In this instance, it would more likely be a faulty thermostat than a faulty heater core, though you won't know until you have them checked.

That being said, before going too much further, I would also check out the seals around your windows. It could be something as simple as a seal leak that is allowing moisture into your car and preventing them from completely defrosting.

Question: What if My Heater Core Connection Is Broken?

If my heater core connection is broken, what can I do to remedy the situation? Do I just need to buy a new one? Can I retrieve a broken connector?

Answer: Call Up an Auto Parts Store and Get a New One

You should be able to call up any auto parts store and get a new one. Last I checked, they're fairly inexpensive. As far as retrieving the broken connector, without more details I'm mostly just guessing as to how much of the quick connector broke off. So, with those guesses, here are some YT videos that I hope will help. If they don't, it'd be best to take the car in to a pro for this one.

Question: What If the Windows Aren't Fogging Up, but I'm Still Getting Coolant on the Floor Boards?

My windows aren't foggy, but I'm still smelling coolant. What if the windows aren't fogging up, but I'm still getting coolant on the floor boards? Thoughts?

Answer: It's Still Worth Investigating

If the windows aren't fogging up, but you're still getting coolant on the floor boards, it's still worth investigating further. That would seem more like a leaky heater hose, but could also be a small hole in your heater core, which would be better to have repaired now, before things get worse.

Most Common Car Problems

Area of ConcernDescription


Of the near-5,000 reported faults since March 2015, expensive gearbox repairs top the list, accounting for 8.4 per cent of all problems.


As cars are loaded with more tech than ever, electrical gripes are the second biggest problem, adding up to 8.2 per cent of all Warrantywise claims.


As mileage racks up, slipping or burnt out clutches can become common, contributing to 7.8 per cent of claims.


One of the priciest faults your vehicle can develop is with the turbocharger. This is increasingly frequent, making up 4.7 per cent of Warrantywise claims.


Having fully functioning brakes is the most vital feature of your car, so it’s disappointing to see faults developing on so many used examples (4.7 per cent).


The traditional alternator could be phased out with the advent of hybrids and electric cars, but it’s an issue in used models, with a failure rate of 4.3 per cent.

Cylinder head gasket

White smoke and coolant leaks are symptoms of a cylinder head gasket failure; 3.1 per cent of cases involved vital gasket repairs over the last year.

Air-con condenser

Air-con is a necessity for those odd hot days. New condensers accounted for 3.1 per cent of problems.

EGR valve

Exhaust gas recirculation valves were at the heart of the recent emissions scandal. Data shows faulty parts made up 2.9 per cent of claims.

Window motor/regulator

Gone are the days of winding your windows down by hand. But even modern motors can burn out; fixes were required in 2.2 per cent of cases.

Share Your Experience, or Ask More Questions

I love to hear old heater core job stories. They can be epic battles, depending on what kind of vehicle we're talking about. If you leave me a question or a story in the comments below, please tell me the year, make, and model of your vehicle.

You're looking for answers, and I'm looking to give you answers! So, you ask them in the comment section below, and I will answer them as quickly and as accurately as I can. Please keep in mind that the more details you can provide about your car and your problem, the better quality advice I can give you.

Also, if you're question is not answered in this article, please check my other articles, as I might just have created a whole new one with your question in mind!

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: My blower motor and AC seem to be working good and I recently changed the thermostat on my 2012 Jeep Liberty, yet it's still overheating. What should I try next?

Answer: Without more information, I would suggest your next step is to check your heater hose inlet and outlet hoses, which come out of the top and rear of your motor, and then into the firewall. If those hoses aren't pinched or broken anywhere, I would recommend replacing your heater core.

Question: Would a leaking heater core cause the driver's side floorboard to be wet?

Answer: Yes. Many vehicles have heater cores that are more centrally placed, meaning it can leak on either side. Though it could also be a leak from your firewall (a grommet or anything similar). Check to see if you're low on coolant and then check to be sure the vents below your windshield are clear and clean.

Question: I have a heater problem, it won’t fully blow heat and doesn’t put out a lot of power. What could be wrong?

Answer: I would first check to be sure you have coolant in your radiator. If it's low or out, you won't get any warm air & that shows you have a coolant leak. If your coolant levels are fine, then replace your blower motor.

Question: My heater was really blowing hot air and then I heard a whine underneath the car, I shut my heater off and it quit. What would cause my car to whine and quit when I turned off my heater?

Answer: I would check your water pump or the blower motor.

Question: I have a 2003 honda civic. Water has been appearing on the driver's side floorboard. Could this still be a bad heater core? I have good heat, though I am losing coolant. Everything I've read talked about the passenger's floorboard, could it still be the heater core if it's leaking on the driver's side floor?

Answer: In most vehicles, the heater core is located over the passenger side; hence the common signs of bad heater cores say to check the passenger floor board. Though many heater cores are placed more towards the center, especially in front-wheel drive vehicles like yours; hence, they can leak on either side. Considering that you are losing coolant/water, it is highly likely that it is your heater core which is leaking.

There are a few reasons you could still be getting heat, though I would focus on your coolant leak first.

Question: I have changed the water pump and thermostat on my 2006 Chevy Silverado 2500hd with a 6.0, and now there is coolant pouring out of the a/c condenser drain tube, but it stopped as soon as I bypassed the heater core. Any ideas what is wrong and what I need to do to repair it?

Answer: Sounds like your heater core is faulty; replace it & it sold resolve the leak from your condenser tube.

© 2014 Wrench Wench

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