How to Tell If Your Heater Core Is Bad or Clogged

Last Updated on January 30, 2022 by Vernon Scott

Having a faulty heater core means that you will not get enough heat on the passenger-side through the blower fan. It can get pretty uncomfortable, especially during a cold winter day. Before you call for a mechanic, you may wonder what the cause of the damaged heater core is. Was it blocked up by something, or is it just bad? We will explain that in detail in this article.

Although, we should mention beforehand that clogging up a heater core is a rare event. It is more unlikely that your heater core is clogged up than bad. But you can still check it.

Ways to Determine What Happened to Your Heater Core

Now, you can’t say for sure whether your heater core is clogged up until you open everything. But that is a job for the mechanic. But you can still determine it to some extent. There can be several reasons behind a faulty heater core. Some of them are-

  • One of the main reasons behind a faulty heater core is corrosion. If your car’s coolant system has rust on it, that can mean that the heater core is clogged up. You can actually understand it by looking into the coolant. If it has liquid with brownish or blackish color, that means there is rust. You can flash the cooling system, in this case.
  • If there was a leak in the coolant, and you have tried to fix it, there can be a scenario. If you have used stop-leaks and the heater core is not working now, it may have blockages.

You can actually test what happened to your heater core using the hoses that come out of the firewall. These are the hoses that feed and return the coolant to the heater core. You can find them near the firewall. Feel them as the engine is running. If one feels totally cool to the touch while the other is hot, your heater core is likely to be clogged up.

In a regular case, both hoses should be hot to the touch.

Frequently Asked Questions about Heater Core

What Should I Use to Clear the Blockage in My Heater Core?

You can use an air compressor machine to force compressed air into the core.

How Many Chances There Are for My Heater Core to Clog Up?

Your heater core will not clog up without any external force. It means that the heater core is more likely to be worse than being blocked. You should still check it before making any move on it.

What to Do If My Heater Core Is Not Clogged Up But Still Not Working?

In this situation, you should consider replacing the heater core. It can only mean that your heater core has gone faulty. The project will be quite costly, though.


You can actually clear the blockage of a heater core using compressed air or appropriate cleaners. In fact, replacing a heater core is so much effort and expense that you may consider any other option before trying that.

All you have to do is run the compressed air and cleaners into the heater core. It will help you rid of the clogging up. It can also save lots of money. Hopefully, you can spend some relaxing time in the heat of your heater core soon.

I am a Trained HVAC Technician and Author of EmiNick. I have been in the industry for over 10 years and have gained a wealth of knowledge and experience. I have been involved in all aspects of HVAC, from design and installation to repair and maintenance. I am also a certified energy auditor and have experience in conducting energy audits for both residential and commercial customers. In addition to my HVAC experience, I am also a certified home inspector and have conducted many home inspections for both buyers and sellers.

We will be happy to hear your thoughts

Leave a reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.