How To Tell If Your Heater Core Is Bad Or Clogged?

Before we diagnose the problem it’s important to understand how it all works. The heater core may be a part of the air conditioning system, but it relies on using a hot circulating engine coolant to deliver heated air into the cabin or for debugging.

In this article, learn how to tell if your heater core is bad or clogged and get cooling air.

How To Tell If Your Heater Core Is Bad or Clogged?

In this case, if you are not receiving warm air inside the cabin or the defogging function isn’t working well. This is the first sign that something may have failed and clogged isn’t the only culprit either. Have you noticed something wrong with your coolant? Here are some signs,

  • Weak or no airflow
  • Cold air comes through the vents when the heater is on.
  •  Coolant leakage is visible inside the cabin or has a damp smell.

A noticeable difference in airflow could indicate that the heater core fins have been clogged and are restricting airflow. The coolant swell or visible coolant leakage inside the car is a bit more sinister. This happens due to the hole in the coolant which escapes into the cabin. This is typically where the heater cores are situated. It is to get the system working although sometimes sealing the leak is possible.

What Causes Antifreeze To Leak?

Coolant leakage inside the cabin can be dangerous for several seasons. The coolant liquid near or on the pedals can make them slippery, and the liquid itself can encourage would or rust which can then corrode the floor of your car. The leakage leads to the problem.

Then your car may be losing coolant level but can’t locate the source of the leak it could be escaping into the cabin of the car. Coolant loss will cause engine overheating which is not good for many parts inside the systems.

How To Solve The Heater Core Problem?

Step 1

Check the coolant level in your radiator and overflow tank before starting the vehicle. The heater core isn’t getting enough fluid circulating into it to warm the vehicle, this leads to a major reason, the low coolant in the radiator. In this case, Fill the radiator and overflow the tank as needed with equal parts antifreeze and water.

Step 2

Determine whether you are smelling antifreeze, seeing wetness on the passenger side floor, or getting a greasy mist on the interior of the windshield when the defroster mode is on the temperature control panel. This may lead to the heater core leaking and will need to be replaced. It will also keep losing antifreeze until it is replaced.

Step 3

Get the engine up to operating temperature and leave it running in park or gear with the parking brake on. Release the hood latch.

Step 4

Locate the temperature gauge on your dashboard and make sure it is running between 190 degrees to 220 degrees. If the temperature mark is not available in an accurate way, then make sure the coolant level is in middle, in the area where it should be. If it’s flat, you may have a coolant level problem or a thermostat problem.

Step 5

Open the hood and locate and try to touch the upper radiator hose to see if it feels warm. Follow the hose to the engine block and touch it carefully down in the area near the thermostat.

Step 6

Now, locate the two smaller hoses that go into the firewall on the passenger side of the vehicle. In some of the vehicles, this process is not that easy and you may have to crawl underneath the vehicle to locate and touch-test them. To the heater core coming from the radiator, the hoses are an inlet, and the other outlet comes from the heater core. If the inlet hose is hot or warm and the outlet hose is cold, you can determine your heater core is clogged.

Step 7

Determine what you want to do, if the heater core hoses are not easily attempted unclogging the heater core yourself, at least you have identified the problem and described it to your experts. If the heater core hoses are not that difficult to access. You can try to flush out the heater core with a garden hose. In this condition, turn off your vehicle and leave it for some time to get cool.

Step 8

Place a drain bucket under the vehicle beneath the hose connections and remove the two hose clamps with a screwdriver or a pair of channel locks. Notice the hose, which needs reinstallation, and allow the heater core and hoses to drain thoroughly.

Step 9

Take a garden hose and insert it into the inlet tube. Be careful how much water pressure you turn on the hose. Some hoses can run up to 100lbs.per square inch of water pressure which depends upon the water pressure which can easily burst a heater core seam. If the water pressure is not enough to blow, add a little more pressure until it blows the gunk out of the heater core.

Now, replace the hoses to the heater core and tighten the clamps. Add antifreeze to the radiator and start the vehicle again with the radiator cap off in case the system needs to burp. Check underneath for clamp leaks and add antifreeze as necessary until the thermostat gauge in the vehicle gets up to operating temperature. You should feel plenty of heat coming from the heat registers now.

How To Test A Bad Heater Core?

Because the heater core is usually tucked away behind the dashboard, testing it can be tricky. In this condition, you have more ways to check for heater core leaks and obstruction.

However, you should make sure the rest of the cooling system is working properly, before testing the heater core. There are a variety of cooling system problems which are ranging from a low coolant level to a faulty water pump that can mimic a bad heater core.

In this case, you can also use an infrared thermometer to test the water core problem. If you don’t have access to use these products you can use your bare hands to perform a less precise version.


If the heater core and the rest of the cooling system are free from leaves the pressure should hold. On the other hand, if the pressure drops rapidly, there is a leak somewhere. While the system is pressurized, you may be able to spot a heater core leak by looking for coolant under the dashboard and on the floor.

We hope that now you know how to tell if your heater core is clogged or bad from this article. If your doubts persist, you can put your comment below in the comment section.

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