How to Replace a Heater Core

Heater core replacement is quite a task for a DIY mechanic, but you can do it with the right tools and enough time. Alternatively, it can be an expensive bill from your local mechanic, so it's worth a shot to save hundreds of dollars if you have some wrenching skills. Here's what you're in for when swapping out heater cores.

 

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How a heater core works

A heater core is one of the critical components of a vehicle's heating system, with the other being a blower motor. Located inside the cabin, a heater core looks like a mini radiator, and that's essentially how it works. Like a radiator, it's connected to the engine's cooling system with inlet and outlet hoses. When the engine is warm, the water pump circulates hot coolant into the heater core and its many small tubes. Turn on the heater, and air blows over the hot tubes and fins, cooling them and transferring the heat to the air. The coolant flows back to the engine, while the warmed air is pushed through the HVAC vents. This is why, on a bitterly cold day, you don't have HVAC heat right away. The engine is cold and hasn't reached operating temperature, so there is no heat to exchange with the air at the heater core, and all you get from the air vents is disappointment.

Symptoms of a failed heater core

The symptoms of a bad heater core are fairly straightforward. The most obvious sign is drips or even a puddle of coolant soaking the carpet in the foot wells. Smelling coolant in the cabin is pretty good sign, too. Then there's the lack of heat. With the engine warmed up, and the heater on, the heater core is probably clogged if you aren't getting warm air. Another sign is foggy windows, as it can't make heat to properly operate the defroster/defogger, and a greasy residue on the inside of the windshield from the defroster vents. Finally, you may find an overheating engine, as the coolant slowly leaves the system a drip at a time.

And since you're probably going to ask: Yes, you can drive with a failed heater core, but it's not recommended. By continuing to drive with it not working, you are attempting to circulate coolant, putting other cooling system components at risk and eventually damaging the entire cooling system. And if you let a leak go for too long, you run the risk of overheating the engine. Having a shop replace the heater core averages $1,000, which is a strong reminder to perform preventative cooling system maintenance on time.

Vehicle System
HVAC
Skill Level
Expert

This is a challenging and technical project

Time to Complete
4 to 6 hours
    Pro Tip

    This job can vary significantly between vehicles, and the following is a general guide that applies to many vehicles in which the heater core is replaced by removing the dashboard. Make sure to read your repair manual before beginning. We also recommend checking the coolant condition before making any repairs. If it looks rusty or has debris in it, it's a good idea to go ahead and flush the system with the old heater core still in. That way you won't have to flush after the new heater core is installed and possibly add debris to the new part.

  1. Have the air conditioning system discharged by a qualified A/C shop. It is under high pressure, and a shop can safely discharge it and store for later disposal.

  2. Ensure the engine and cooling system are entirely cool before proceeding.

  3. Disconnect the negative battery terminal.

  4. Set a catch pan under the engine, and drain the cooling system. Store the coolant for disposal later.

  5. Depending on your service manual, you may have to remove just a section of the lower dashboard or the entire dash, instruments, and accessories. Start by removing the lower dash panel and have a look with a flashlight. If you can immediately see the heater core, then odds are the dash doesn't have to come out. For example, on the third-generation Chevy Camaro, you can remove the top dash pad, the passenger side speaker, and push the PCM aside, then easily access the heater core from below. On the other hand, the eleventh-generation Ford F-150 requires removal of the air bags, instrument cluster, entire dash, and dash frame, before accessing the heater core.

  6. Pro Tip

    As you remove panels, trim pieces, and bolts from the interior, label them with their sequential order and tape them to the part in plastic bags. A marker on masking tape will work. Be gentle with clips and connectors, as they're pretty delicate and can become brittle on an older vehicle.

  7. Disconnect the two heater inlet/outlet hoses at the firewall. Plug all the open lines and fittings to prevent contaminating the cooling system. Depending on the model, remove the air conditioning accumulator.

  8. Remove the temperature blend door actuator, then disconnect any remaining electrical connectors.

  9. Remove the plastic heater core cover. Some bolts are likely out of view, and extensions and a U-joint drive will help the socket find them.

  10. Remove the mounting fasteners from the heater core. Pull the heater core away from the firewall, being careful not to damage the tubes.

  11. Installation is the reverse of removal.

  12. Pro Tip

    Many DIYers find it difficult to properly align the new heater core as the inlet/outlet tubes protrude into an area that is difficult to view. An easy way to ensure proper alignment is to get the heater core halfway set, then, from the firewall, stick a gloved finger through the firewall and into the outlet tube and guide the tube through the firewall. Then press the rest of the way from the cabin side.

  13. Use new O-rings in the A/C connections to ensure a water-tight seal. Make sure all dashboard panel fasteners are tightened, or you will have rattles.

  14. Refill the cooling system and bleed air out. Have the A/C system charged.

Last updated March 18, 2019

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