What Is a Heater Core? What Are the Signs That It Is Going Bad?


Sep 24th, 2020

What Is a Heater Core? What Are the Signs That It Is Going Bad?

Not a lot of people know about their car’s heater core. Have you read our article about engine overheating in vehicles? If you have, you will recall our advice about opening the windows and cranking the heater up with the fan at full blast. It underscores the fact that heater cores and engines share more than a few components under the hood. Let’s find out what a heater core is and what the signs of a faulty heater core are.

What is a heater core?

The heater core is the central part of your car’s heating system, which derives heat from the engine’s cooling system to warm up the passenger’s compartment and defog windows in cold weather. That statement can be a bit confusing if you’re clueless about an automotive cooling system

Here's a quick detour then: A car's cooling system uses a liquid coolant that circulates the engine block through pipes, absorbing heat as it does. The hot liquid is then pumped to a heat-exchanger (the radiator) which has the job of cooling the liquid before it is circulated back to the engine. 

So where does the heater core figure in the cooling process? 

The heater core is often referred to as a ‘small radiator’ because it looks and works like a radiator, except that it is smaller than a radiator and draws heat to use for its purpose. In comparison, a radiator draws the hot coolant to cool it. 

So going back a bit, the water pump forces the hot liquid through loops of pipes in the circuit, but is directed to the heater core through a valve or door before it flows back to the cooling circuit. This constant flow of hot liquid through the heater core warms the air (by heat transfer) which a fan blows towards the cabin. 

What are signs of a failing heater core?

The same issues that cause failures in the cooling system may also affect the performance of the heater core. For instance, clogs or leaks in the system will cause engine overheating due to poor circulation of the coolant. Clogs, or defective valves in many cases, may cause the hot liquid to bypass the heater core. Leaks, on the other hand, will deplete the coolant fast, causing the engine to overheat and the heater to not work. Also, coolants contain corrosive components, which are a major contributor to contaminants and leakages in both the cooling and heating circuits. 

There’s no doubt about the urgency of resolving problems in the heater core promptly to prevent them from worsening and affecting the engine. Periodic flushing and inspection can help nip problems in the bud. 

Below are telltale symptoms that you shouldn’t ignore; they could be signs of a bad heater core or one that’s about to fail.

  1. Slimy fog on the windshields – when you notice a slimy film that forms foggy patches on all your car windows, it could only mean one thing – a leak in the heater core. Coolant mist combines with the warm air blown into the cabin, evaporates and settles as greasy fog on the cold window glass. 
  2. Odd sweet odour – sweet-smelling air coming through the heater vents is a sure sign of a leak through the heater core. What you’re detecting is the coolant, which has a fruity smell. It does not only mean that your heater core is going bad, but also that your car’s cooling system is compromised. 
  3. Cold air blowing through the vents – warm air can escape through holes and cracks, lowering the temperature of the air entering the cabin. Check for coolant spills on the ground where you park. A wet passenger-side floor can also indicate a damaged heater core. Cold air from the heater can also be an issue of a faulty control valve or blend door, which is responsible for mixing the hot heater air and cold outside air. 
  4. Constantly low level of coolant – if you find yourself frequently replenishing the coolant, it can be caused by a blown heater core. The culprit, though, can also be cracks or leaks elsewhere in the cooling system. In any of these cases, your cooling system will also be affected. 
  5. Heater not working but cooling system is fine – in the first four symptoms, they will mostly be accompanied by signs of engine overheating. But what if there are no signs of overheating? Then it could be a problem solely with the heater core – possibly a clog that prevents the hot coolant from entering the system. It could also be a stuck or broken heater control valve can restrict flow to the heater core or bypass it entirely.

So what if the heater core goes out? Is it okay to drive with a bad heater core?

If your heater core goes out, is it safe to ignore it? While you can bundle yourself up and bear the cold, it's still not a good idea to ignore a heater core that goes bad. Why? 

First, if the cause of your heater core going out is a leak, blown heater, or defect in the automotive cooling system, then you should resolve it immediately. You don’t want to turn a blind eye on something that poses a risk to your engine. 

Second, if you’ve read our piece on engine overheating, you’d know how important a heater is in the event of an overheating emergency. 

The bottom line is that you should get that faulty heater core inspected and repaired. Locating A1 spare parts is not difficult, especially with Carpart.com.au. We invite you to visit us – learn from our blog, search auto parts online, and sell used car parts through the Ads section. Start here