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How to flush a heater core – A step-by-step guide

  • Car Care Tips
  • Renee Martin
  • 3 minutes

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Is your car’s heater not working properly? This could be because of a clog in the heater core. Don’t worry – you can perform a heater core flush at home with the right equipment and correct techniques. Here’s our detailed guide on how to flush a heater core. Use this to unclog your heater core without any hassle.  

Before we delve into how to unclog a heater core, let’s first understand what’s a heater core and its function.   

What’s a heater core?

A heater core is a device that warms up a car’s cabin. It uses the heat from the coolant and warms the vehicle’s interior. So, when a heater core is clogged, it prevents the coolant from passing through it. Therefore, the amount of heat transferred into the cabin also decreases. This is where a heater core flush can help you.   

Now let’s dive into the important part.

How to flush a heater core- car owner checking the heater core

How to flush a heater core

Things you’ll need   

  • Bucket  
  • Garden hose  
  • Container   
  • Screwdriver  
  • Duct tape 
  • Coolant water mixture

Step 1  

The first step is identifying the heater core inlet and outlet hoses. It’s usually located on the car’s firewall. However, the location can vary based on the vehicle. So, if you have trouble locating them, refer to the vehicle owner’s manual.  

Step 2   

Next, disconnect the heater hoses. Use a screwdriver to loosen the hose clamps. While disconnecting the hoses, water and coolant can pour from them. Therefore, place a container below the hoses and point the inlet hose down towards the container.  

Step 3  

To clean the blockage, you need to flush water or air through the heater core. By doing so, the grime and dirt that’s causing the clog will come out through the inlet hose. Now, insert a water hose into the outlet hose. If you have access to an air compressor, you can use that to push out the coolant and grime. Use a seal or duct tape to connect the outlet and hose tightly.  

Step 4   

After sealing the outlet tightly, turn on the water. If you’re using an air compressor, turn that on. After some time, the remaining coolant, water, and grime will flow through the inlet hose into the container. Let the water flow for a few minutes to remove the clog. Turn off the water and allow the system to drain.   

Step 5  

Reconnect the hoses back to the system and fix the clamps back. Make sure the connections are tight. Now, it’s time to refill the coolant system. Open the radiator cap and fill it with a 50/50 mixture of water and coolant, or you can use a premixed coolant that is readily available.   

Step 6  

Go out for a drive to test the system. Turn the heat to the maximum level. After a while, warm air should be coming out of the vents. Finally, check if there are any leaks in the hoses.   

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