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How to Back Flush Your Heater Core by Yourself

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  1. step : Identifying the Heater Hoses (0:40)
    • Run the engine until it reaches its operating temperature
    • Turn the heater all the way up
    • Locate the heater core hoses, near the firewall
    • Feel the heat coming off the hoses
    • The hotter hose is the inlet hose
  2. step : Flushing the Heater Core (1:56)
    • Remove any components blocking access to the heater hoses
    • Have a drain bucket ready
    • Block the heater hoses with block off clamps
    • Allow the engine to cool down
    • Disconnect the heater hoses
    • Connect two rubber hoses to the heater inlet and outlet
    • Connect a water hose to the rubber inlet hose
    • Run water through the inlet hose at low pressure
    • Remove the two hoses from the heater core
    • Dispose of the coolant properly
    • Connect the heater core hoses to the heater core
    • Remove the block-off clamps from the heater hoses
    • Reinstall any components you removed to reach the heater hoses
    • Add coolant to the cooling system as necessary

Hi, I'm Mike from 1A Auto. We've been selling auto parts for over 30 years. We're dedicated to delivering quality auto parts, expert customer service, fast and free shipping, all backed by our 100% satisfaction guarantee. Visit us at 1AAuto.com, your trusted source for quality auto parts.

If your heat isn't coming on or isn't coming out as hot as it used to, there's a possibility your vehicle has a clogged heater core. If you have no signs of leaks, full coolant and proper flow through the rest of the system then flushing out your heater core backwards could be an easy solution to making your heat work like it used to.

Locate the heater core hoses on your vehicle. They'll usually run to two ports coming out of the firewall on most trucks and cars. On our truck our two heater core hoses can be located here. What we're checking is by allowing the vehicle to run and warm up, I also have my heat on full blast, we'll either have a decent flow that's still allowing heat to be taken out of the heater core which will bring one hose hot coolant into the heater core and cooler coolant out of the other side or if our heater core is clogged we'll have hot, hot coolant on one side and an ice cold hose on the other. This will tell us which is inlet and which is outlet so we know how to back flush it correctly. This hose is much hotter than the other one so we know we have hot coolant coming in here and cold coolant coming out the other side if at all so this is our inlet, meaning we want to hook up our reverse flush set up to this side, the outlet, to push all that dirt, debris and contaminants out the other way.

After figuring out which heater core hose is which, you'll want to remove any components blocking your access to the lines. In our case this is the intake track on our truck.

Place a drain bucket under the lines to the heater core hoses. Now there are a few options on exactly how you want to go about doing this. It's not a bad idea to drain your entire cooling system and then flush the heater core hoses after all the coolant is out of the system, especially if any of that stuff has freed up and contaminated your system. We just filled our coolant when we did our head gaskets a few weeks back and we don't want to waste it so a set of radiator hose lock off clamps is inexpensive and a great way to keep the mess to a minimum. Simply clamp them on to seal off the hose. Now when I remove this end the only coolant we'll lose is from the heater core.

Allow your cooling system proper time to cool before removing the hoses because even with our block off clamps we are still going to lose a little bit of coolant and you don't want to get burned. We'll slide the clamps off and wiggle our hose off. That little splash there is just from our exhaust manifolds being hot. Our coolant is actually not that bad right now. You can see there where we are losing some coolant, we did lose a considerable amount less than we would have if we drained our entire system.

This is clear five-eighths rubber hosing, which is what we're going to use to run the water through. Yours doesn't necessarily need to be clear. It makes it helpful for watching the dirt and debris come out but we wanted to use the clear stuff so you really get an idea of how much gunk can get clogged up in these. We'll put the short one on to the outlet side and a longer one on to the inlet side, which we'll also run down into a bucket.

I have some fittings here on the end of the hose that I just got at the hardware store to reduce it down to five-eighths and give us a nice solid connection. You don't want to run a lot of pressure through this. Your cooling system really doesn't build more than 12 pounds at most on most vehicles. Just a little bit of pressure is more than enough.

It looks like ours isn't as clogged as we thought. We're getting a good flow and not a lot of debris. That first push did put some gunk out of it. Once you have a good, clear flow of fluid coming out like we do now we'll go ahead and let that finish running out.

Remove our flushing hoses and make sure you've disposed of the coolant you did push out properly. Even though it is diluted with water, you do want to bring it to a proper disposal place. We'll remove these and reinstall our heater core hoses.

Make sure that both hoses and their clamps are in place before you remove the block off clamps if you use them otherwise it'll just leak through one way, fill the heater core and come out the other side. Remove your block off clamps if you used them. Reinstall any components you removed to access your heater core and fill and bleed your coolant with the appropriate coolant.

Now we have a coolant containment tank on site that we have dumped regularly. You'll want to check your local laws as well as local disposal plants and potentially parts stores on how and where to dispose of coolant safely and legally.

Thanks for watching. Visit us at 1AAuto.com for quality auto parts, fast and free shipping, and the best customer service in the industry.

Tools needed for replacement:

    General Tools

  • Drain Pan
  • Funnel

  • Materials, Fluids, and Supplies

  • Rubber Vacuum Hose


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