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Heater Core Replacement: A Beginner’s Guide

Heater Core

Heater core replacement is one of those jobs you have to do if the windshield fogs when the defroster is running. Another visible sign of trouble is damp carpeting, usually on the passenger side of the vehicle near where the heater core is located. When working properly, the heater core sends heat to the cabin. When it leaks, it must be replaced. Getting the job done ranges from easy to difficult, depending on the core’s location inside your car.

Don’t Delay

Besides not functioning in the way intended, a leaking heater core creates a mess. The liquid is coolant, also known as antifreeze, and it can damage your car. Antifreeze is also toxic and if somehow ingested, it can make a person very ill. Ethylene glycol, methanol and propylene glycol are among the main ingredients present and may lead to serious symptoms and even death if consumed and not immediately treated. Even if you don’t drink the liquid coolant directly, the vaporized coolant can still circulate inside the vehicle. If that vaporized coolant ends up in your lungs, it can make you and your passengers sick. So don’t put off a heater core replacement thinking you can just keep adding coolant, the damage can reach farther than you think.

Locate the Heater Core

Where did the manufacturer place the heater core? You may need to reference a service manual to find it, but it’s typically found in one of two areas.

Heater Core Replacement

Lift the hood and follow your car’s cooling system towards the cabin to find what looks like a small version of your vehicle’s radiator. Two hoses connect to the heater core — one hose is tasked with transporting hot coolant from the water pump to the heater core. The second hose returns the coolant to the top of the engine. These hose connections are usually found on the passenger side of the engine firewall, but may also be found near the middle. A blower or fan draws air through the heater core, directing air through the heater ducts to your car’s interior.

Unfortunately, not all heater cores are prominently located. Some are located inside the dashboard. That means you’ll have to remove the dash as well as the heating, air conditioning and ventilation (HVAC) system to reach it. In this example, you’ll have to evacuate the air conditioning system as a result of disconnecting the evaporator to remove the HVAC unit. It’s at this point you may decide to let your mechanic handle the job.

Completing the Job

You’ll need several tools to get this job done, including a jack, jacks stands, a socket set, wrenches, pliers, a drain pan and rags. Besides a new heater core, you’ll also need coolant. You may need heater core hoses and hose clamps.

When you find the heater core, raise the front of your vehicle, placing it on jacks. Drain the coolant from the radiator. Next, remove the heater drain tube and loosen the clamps on the heater core hoses. Remove the hoses connecting to the heater core. Inspect the hoses, as now would be a good time to replace them if they are rotten. Drain whatever coolant remains.

Before installing a new heater core, transfer any parts from the old heater core to the new one. Install the new core, reinstall or replace the mounting clamps and then the hoses as well as the heater drain tube. Once the heater core, clamps, hoses and tube are secure, you’re ready to add new coolant to the radiator. Once filled, lower the vehicle.

Start the engine, turn the heater on high and activate the fan to verify heat is blowing from the heater core. Once you’re confident everything is working as required, all that is left is clean up. If the heater core came with an access cover, then install it. Recheck the radiator to ensure there is enough coolant present as air pockets may escape the system and need additional fluid.

This job is doable, it just ranges from easy to challenging, depending on where the heater is located inside your car.

Check out all the heating & cooling parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on heater core replacement, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

Matthew C. Keegan View All

Matt Keegan has maintained his love for cars ever since his father taught him kicking tires can be one way to uncover a problem with a vehicle’s suspension system. He since moved on to learn a few things about coefficient of drag, G-forces, toe-heel shifting, and how to work the crazy infotainment system in some random weekly driver. Matt is a member of the Washington Automotive Press Association and is a contributor to various print and online media sources.

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