Heater Core Replacement


heater core replacementHeater core replacement is one of those jobs where the parts are relatively inexpensive so it may seem like a simple job, but in reality, it usually ends up being a very expensive undertaking due to high labor costs.  Heater cores can require replacing either because they get clogged or because they start to leak.

If your heater core ends up clogged you can try flushing your cooling system to remove the clog and get coolant flowing through your system again.  You can identify a clog in your heater core by checking the inlet and outlet temperatures at the heater lines going through your firewall.  If there is a large difference in temperature (more than 10-20 degrees) when the heater is off then you most likely have a clog. If you cannot unclog your heater core by flushing it then you must replace it.

The other problems heater cores have is leaks.  Leaking heater cores often result in coolant dripping from your AC condensate drain or onto the passenger side floorboard.  While these leaks are usually slow enough that they won’t lower your coolant level very quickly they can be messy and make the ventilation system in your car dirty and smell awful.

Heater core replacement can be broken down into a few difficult steps:

Heater Core Replacement

  1. Drain your cooling system
  2. Remove the heater core hoses
  3. Remove your dashboard
  4. Replace the heater core
  5. Reassemble and refill your cooling system

Drain your cooling system

You have to start by draining your cooling system so you can safely remove your heater core hoses without making a mess.  Since your heater core is high in the system you often only have to drain ⅓ to ½ of the system volume to empty the heater core.  

Remove the heater core hoses

The coolant hoses that carry water to and from your heater core will often connect to your water pump, a cooling system manifold or the cylinder head back by the firewall.  These hoses are usually about 1” in diameter and will be the only coolant hoses that pass through the firewall. These hoses may have simple clamps securing them to the heater core or they may have special fittings that require a unique tool to disconnect.

Remove your dashboard

This is the part of the heater core replacement that adds all the cost at your local mechanic.  Your heater core is tucked away in your ventilation system which sits behind your dashboard. In most vehicles, the dashboard has to be removed or at least slid back from the windshield a foot or so to gain access to the heater core.  

Replace the heater core

Once you have access to the heater core you may have to loosen some of the ventilation box mounts to have enough room to sneak the inlet and outlet pipes through the firewall, or those pipes may detach from the heater core entirely.  Be careful when installing the new heater core to avoid damaging any of the cooling fins.

Reassemble and refill your cooling system

Once you’ve got your new core in, it’s time for reassembly!  It is wise to try connecting the new heater core and refilling the cooling system to check for leaks before you reinstall the dash to save some time if you’ve made a mistake or need to make any adjustments.

If this whole procedure seems daunting, you’re right!  Many dashboards have suffered cracks or creases during heater core replacements.  Also, new cars may have airbags that need to be moved to be careful and make sure you’ve got a good repair manual if you attempt this job yourself.  If you need a quick for your leaking heater core, consider using BlueDevil Pour-N-Go to seal the leak in your heater core rather than going through all that work.  BlueDevil Pour-N-Go can seal the leak in your heater core saving you time and money!

You can find BlueDevil Pour N Go Head Gasket Sealer at any of our partnering local auto parts stores like:

  • AutoZone
  • Advance Auto Parts
  • Bennett Auto Supply
  • CarQuest Auto Parts
  • NAPA Auto Parts
  • O’Reilly Auto Parts
  • Pep Boys
  • Fast Track
  • Bumper to Bumper Auto Parts Specialists
  • S&E Quick Lube Distributor
  • DYK Automotive
  • Fisher Auto Parts stores
  • Auto Plus Auto Parts stores
  • Hovis Auto & Truck Supply stores
  • Salvo Auto Parts
  • Advantage Auto Stores
  • Genuine Auto Parts stores
  • Bond Auto Parts stores
  • Tidewater Fleet Supply
  • Bumper to Bumper Auto Parts
  • Any Part Auto Parts
  • Consumer Auto Parts

Pictures Provided By:
heater_core_replacement.jpg – By Chiewr – Licensed by Getty Images – Original Link

30 responses to "Heater Core Replacement"


  1. DALE on October 24, 2019 at 9:04 am

    will blue devil clog a heater core up or coat the tubes and reduce the flow?

    • BlueDevil Pro on October 24, 2019 at 10:07 am


      The BlueDevil Head Gasket Sealer does not contain any solid or particulate matter, so it is a non-clogging product. Specifically, the product is attracted to air flow, so it won’t just go in and coat the whole system. It is specifically attracted to where there is a leak.

      Thank you!


  2. Jaime on October 11, 2020 at 9:38 pm

    What could happen if blue devil is applied through the resivoir instead of the radiator?

    • BlueDevil Pro on October 12, 2020 at 8:26 am


      The product will not enter the cooling system quickly enough. The reservoir does not circulate continuously. By the time it started pulling from the reservoir the engine would already have produced heat. The product reacts around 150 degrees Fahrenheit, so this means the product could start reacting before it was able to circulate and the chance of BlueDevil working would be greatly decreased.

      Thank you!


  3. Tony on December 29, 2020 at 10:00 am

    So you just pour blue devil in through the regular radiator do you pour it while car is on or off

    • BlueDevil Pro on December 29, 2020 at 12:10 pm


      When the engine is cold, you would start the vehicle, put the heater on and blower to the max and then slowly pour the product in through the radiator cap. Put the cap back on and let the vehicle sit there and idle for 50 minutes.

      Thank you!


  4. K on January 17, 2021 at 12:54 pm

    Will it still work in radiator if your heater doesn’t heat but still comes on

    • BlueDevil Pro on January 18, 2021 at 8:22 am


      The motive behind putting the heater on, in regards to using BlueDevil, is to draw heat from the engine to help it from overheating during the 50 minute idle. As long as the engine isn’t overheating, the product would still be able to seal.

      Thank you!


  5. Brad on October 22, 2021 at 9:02 pm

    I removed my thermostat as the directions said but my vehicle was only able to idle for about 20 minutes before it started to overheat. The Jeep was not overheating before I tried using Blue Devil head gasket sealer. I was losing coolant slowly but never overheated because I kept the coolant full. Older Jeep Cherokees have small coolant systems and this may be why it started to get hot with the thermostat removed and unable to idle for the entire 50 minutes.
    Did I cause more harm by shutting the vehicle down before reaching the 50 minute time limit? What should I do next? Thanks

    • BlueDevil Pro on October 25, 2021 at 8:13 am


      Thank you for asking about your Jeep Cherokee. With the thermostat removed, the vehicle should be running cooler than normal, as the coolant would be free-flowing and allow for better overall circulation. What are the symptoms the vehicle was having? Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  6. Darrell Eng on November 19, 2021 at 1:08 am

    I have a 2002 Toyota Echo. As the heater core started to leak, I disconnected the hose to and from the heater core so that it does not work. I saw your Pour-N-Go Head Gasket product and thought I would give it a try. What is the best way to maximize the effectiveness of your product to fix the leak in the heater core? Should I reattach the hoses so that coolant flows through the heater core, and then pour the product into my radiator? Or should I do something else?
    Thank you.

    • BlueDevil Pro on November 19, 2021 at 8:20 am


      Thank you for asking about your Toyota Echo. When using the BlueDevil Pour-N-Go Head Gasket Sealer, you would reconnect all the hoses so that it is a closed system. The product would be added when the engine is cold, directly into the radiator, and not in through a reservoir/overflow tank. You would also put the heater on, blower to the max so that coolant/BlueDevil is flowing through the heater core. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  7. Lori on January 28, 2022 at 4:55 pm

    I have Chevrolet Ventura and the heater core is needing replaced but can’t afford right now so would blue devil work just for now

    • BlueDevil Pro on January 31, 2022 at 8:04 am


      Thank you for asking about your Chevy Ventura. Is the heater core leaking coolant? If so, are you losing a lot of coolant or is it more of a slight leak. Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  8. Will on February 28, 2022 at 7:24 pm

    I have a 2008 Infiniti G35S. My car was overheating and I had to get it home so I drove with the heat s and ll the way up for about 20 miles. The radiator hose near the fire wall burst spewing coolant everywhere. I patched it with clamps and kept going. As i s as lost made it my engine just cut. Lights and radio stayed on but engine shut off. The car will crank now but won’t start. I’ve replaced the crankshaft sensor I still have spark. I changed the oil as and it was very milky can I use and should I use blue devil without it starting and will it get it started. Thanks

    • BlueDevil Pro on March 1, 2022 at 8:25 am


      Thank you for asking about your Infiniti. In order to get the benefit of using the BlueDevil, the vehicle would need to be able to start and run for a full 50 minutes, without overheating or stalling out. Based on your description, the leak you have may be a little larger than what the product is intended for. A hard part repair may be your best option.

      Thank you!


  9. Jesse on May 14, 2022 at 12:01 am

    I have a SR5 2008 kun26r hilux, it doesn’t have a radiator cap it only has a reservoir, it does have a bleeder at the top of the radiator though would I just pour it into the bleeder hole? Or would it be ok to put it in the reservoir? I really appreciate any information thank you!!

    • BlueDevil Pro on May 16, 2022 at 8:38 am


      If your vehicle only has a reservoir/overflow rather than a radiator cap, instead of pouring BlueDevil through the reservoir/overflow, with the car off and engine cold you should disconnect the top radiator hose and add the product there; do not pour it into the reservoir. It may be added into the hose or the opening on the radiator. Once BlueDevil has been added, reconnect the hose and start the idle from that point.

      Thank you!


  10. Julia Carey on November 30, 2022 at 12:03 pm

    I have a Chevy Tahoe hybrid and it started leaking out of the rear passenger wheel well area. It overheated. I pulled over and had to add 1 1/2 gallons. 2 days later it was down a gallon. They told me it needs a rear heater core. Will your product work to permanently seal this leak or should the heater core be replaced. It has 141,000 miles on it.

    • BlueDevil Pro on November 30, 2022 at 2:51 pm


      Thank you for asking about your Chevy Tahoe. The BlueDevil Head Gasket Sealer would be able to treat a leaking heater core, however, the product is intended for leaks that are seeping or lightly dripping. As long as you aren’t losing water/coolant too quickly, you would be a good candidate for the product. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  11. Steve on January 22, 2023 at 8:44 am

    I have a heater core leak in my 88 Jeep YJ. Should I flush my system and refill with coolant before using Blue Devil, or fill to appropriate fill line (since it has been leaking) or could I just pour in cold and run for 50 minutes if my engine has not been close to overheating?

    • BlueDevil Pro on January 23, 2023 at 8:58 am


      Thank you for asking about your Jeep. If the cooling system hasn’t been flushed recently, it would be a good idea to flush the system to ensure it is clean and free-flowing. This will give the BlueDevil the best chance at working properly.

      Thank you!


      • Chris on March 13, 2023 at 11:14 am

        I have a 2007 dodge nitro 4.0. The headgasket has a minor leak. The oil has a darker brown color to it and two cylinders have lower compression than the others 130psi, 100 psi. My question is should I use the pour and go or the blue devil regular headgasket sealer? Which sealer is better ? Also it ok my heater core is bypassed when using blue devil?

        • BlueDevil Pro on March 14, 2023 at 8:55 am


          Thank you for asking about your Dodge Nitro. You may use either of the Head Gasket Sealers that we manufacture. The “Pour N Go” (16 oz./white label) is an easy to use, less concentrated formula that does not require the removal of the thermostat or a flush of the cooling system prior to use. Whereas the “Mechanic Approved” (32 oz./yellow label) requires both the removal of the thermostat and a flush before applying the product; the 32 ounce (yellow label) is the more concentrated formula.
          The product with the yellow label will give you best overall results as long as you are willing to remove the thermostat and flush the system prior to use. You would use 16 oz. of the product either way. As long as the engine isn’t going to overheat during the 50-minute idle, it would be fine to have the heater core bypassed.

          Thank you!


  12. Lee Jeong on July 5, 2023 at 11:45 pm

    After adding the Blue Devil, it was left at the highest temperature and maximum wind for 50 minutes. Could it possibly block the heater core?

    • BlueDevil Pro on July 6, 2023 at 8:35 am


      The BlueDevil Head Gasket Sealer does not contain any solid or particulate matter, so it is a non-clogging product. The reason for that direction, with putting the heater on with blower to the max, is to help draw heat from the engine to help it from overheating during the 50-minute idle.

      Thank you!


  13. Lee Jeong on August 4, 2023 at 9:42 am

    The first try of Bule Devil was failed. I guess that inside was so dirty so I did linse inside with distilt water 2 times. and I tried this again(second time) and it worked and no more water refiil needed morning time. This is seen city driving only. I din’t go free way yet. can I dive 4 hours long from south of Michigan to the northern Michigan? If this have worked now, Can I try to drive long distance?

    • BlueDevil Pro on August 4, 2023 at 11:03 am


      Once the product seals, it would be a permanent seal. If you are not seeing any symptoms of the leak, you would be fine to drive the vehicle like normal.

      Thank you!


  14. lee on August 15, 2023 at 5:05 pm

    my 600 miles’ travel was perfect. that mean that I can drive this car without worry of overheating as long as blue devil is remain in coolant? I have another question. currently blue devil + distilled water is in my ladiator and engine. should I need change them to blue devil + antifrize before winter?

    • BlueDevil Pro on August 16, 2023 at 8:27 am


      The BlueDevil Head Gasket Sealer only goes through one heat cycle. After the 50-minute idle is complete and the vehicle has had sufficient time to cool down, the product wouldn’t continue to react or continue to seal. At this point, you would be fine to drain the system and refill with your regular 50/50 mix.

      Thank you!


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