The heater core is part of your semi truck’s HVAC system that provides heat for your truck.  Here at Shoreline Truck Parts, one of our goals is to keep you warm during the colder months. This blog will discuss the symptoms of a bad heater core on a semi truck so you can ensure that you have heat when you need it.

What Are the Symptoms of a Faulty Heater Core?

A bad heater core can be detected through the continuous flow of cold air, fog buildup on the windshield, and coolant leakage. Let’s go through these symptoms one by one to learn how to mitigate their severe effects on the HVAC system:

1. Cold Air Coming through the Vents

It’s essential to know that the heater core provides warm air to your semi truck’s cabin by allowing your motors coolant to flow through it. Your blower motor pushes air through the fins of the heater core. The heat is then transfered from the hot coolant into the air in your cab.

Read our guide here to learn more about how your heater core functions.


Sample of a bad heater core. (Source)

It’s unfortunate when you turn on your heat, but only feel cold air coming through the vents. This doesn’t always mean that your heater core is damaged, it just means that you aren’t getting coolant from the motor into your heater core. Some trucks have a manual coolant shutoff by the engine block while others will have an electronic solenoid/actuator shut off. Be sure these shutoffs are open and allowing coolant into your heater core. 

2. Frosted Windshield

Aside from providing warm air through the cabin, it’s also the heater core’s job to defrost the windows and the windshield. If frost is building up on your windows, this could be caused by several things:

  1. You’re not getting enough heat through your vents due to a bad heater core.
  2. Your blend door (the part of your HVAC system that forces air on your windshield) may be malfunctioning.
  3. You have an obstruction in your HVAC system or the blower isn’t functionoing properly. When it comes to obstructions, sometimes the heater core just needs to be cleaned throughly.

We will continue to troubleshoot below.

3. Coolant Leakage

It’s pretty easy to spot a coolant leak, as it creates a green or pink puddle under your truck. Or in some cases, on your carpet inside your truck. If you spot a leakage, determine where it is coming from, it could be anything from a heater core, a radiator or a return coolant line. This needs to be fixed to enusre that your truck doesn’t over heat. 

5. Sweet Smell Circulating in the Cabin

Antifreeze leaking within the system can produce a sweet and syrup-like aroma within your cabin. When this happens, track down the lead and fix it as quickly as possible. 


  Inhalation of refrigerant and coolant can cause potentially serious health issues.

6. Overheating Engine

While the heater core uses coolant to produce warm air, the engine needs coolant to maintain its optimal working temperature. A leaking or clogged heater core can prevent the engine from maintaining the coolant supply it needs. Thus, causing it to overheat.

An overheating engine can cause severe damage to your motor. Once the temperature gauge or the engine warning light on your dashboard appears, refrain from driving your semi truck and get it checked by a professional.

High-Quality Aftermarket Heater Cores

Semi truck heater cores are more susceptible to failure than those in cars due to the higher workload they experience. It is inevitable that you will need to replace the heater core in your truck.


High-quality aftermarket heater core

Ensure Warm and Comfortable Rides with a Fully-Functional Heater Core

If you have determined that your heater core needs to be replaced, we can help you out. We stock many Kenworth heater cores and plan to stock more brands soon. 

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