Clogged Heater Core, How To Fix It

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  1. 02-21-2021, 06:11 PM #1 foama
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    foama is offline Senior Member Join Date May 2014 Location Country is Europe, state is Germany Country Germany Posts 2,249 Garage
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    how to fix clogged heater core

    My heater core became partly clogged during the first two years or so, and didn't heat very much any more. The passenger side was heated worse than the driver side. There are a few threads about clogging heater cores in this forum. In short, especially 2014 - 2015 cars can suffer clogged heater cores because of chemical reactions between OEM coolant and the heater core. This was cause for flushing out and replacing the OEM coolant with some better and more suitable product four years ago. The clogging neither worsened or improved after that, but stayed as it was at the time of flushing and changing the OEM coolant. After some clarifying research I finally got round to fix it. This is how the partly clogged heater core was fixed: For better access the air filter box was removed and put out of the way. The heater core was disconnected from the coolant circulation. To do that, both hoses were disconnected from the core, and a U-shaped bypass connected to the hoses instead. The bypass is about 19m or 3/4 inch in diameter. See: Name: Bypass tube.jpg Views: 2518 Size: 86.1 KB Two short pieces of 3/4 inch garden hose were connected to the core, and the open ends left pointing upwards. A special cleaning fluid was filled into the core through the hoses, and it remained there for two days. The recipe for the cleaning fluid: Two full mugs of water plus two tablespoons of 9% ammonia water (spirit of ammonia), and one tablespoon of your favourite household cleaner. Name: hoses.jpg Views: 2651 Size: 94.4 KB After soaking for two days, the two short snips of hose were disconnected and discarded. A working garden hose was connected to one side of the heater core, and the tap turned on full blast for one minute. Then the hose was connected to the other side of the heater core and flushed full blast in the other direction for a minute. The hoses were swapped and flushed in both directions a few times. The obstructing substance was sucessfully flushed out! NB: There is not much point in doing this if the OEM coolant was not thoroughly flushed out and replaced. If not done yet, this may probably be your last chance. A test showed the heater core works properly again, the temperature on both sides is practically the same. This procedure is easier and much cheaper than a replacement.
    Last edited by foama; 02-25-2021 at 06:38 PM.
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  3. 02-21-2021, 06:31 PM #2 dspace9
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    dspace9 is offline Senior Member dspace9's Avatar Join Date Dec 2016 Location Canada Country Canada Posts 3,061 Garage
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    I had a good test run this morning of my heater with a cabin air filter in it. My Mirage didn't come with a cabin filter eh, I mentioned this in another thread. But I will say that at -16 Celsius at 7 AM this morning (said 9 Fehrenheit on my actual indoor/outdoor thermometer at my house ) that my cold winter start and drive was less foggy, with more heat than it has for years in my Mirage. I even turned the heat down, and I was getting 5.5 L/100 kms gas milage according to the computer. So not to babble on, but I would make sure your Mirage has a good cabin filter. I'm sure you and others are way more on top of this stuff than I am. The brand I bought is from Germany actually, called Corteco "micronAir" cabin filter. They make all sizes, the how-to diagram had an actual autocad type of Mirage graphic. Fit like a glove anyway just a thought on the topic of heat and your Mirage cheers.

    __________________________________________ click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 42.2 mpg (US) ... 17.9 km/L ... 5.6 L/100 km ... 50.7 mpg (Imp)

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  4. 02-21-2021, 07:36 PM #3 Top_Fuel
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    Top_Fuel is offline Senior Member Top_Fuel's Avatar Join Date Feb 2016 Location Ohio Country United States Posts 3,902 Garage
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    That's great news, foama! This is going to save Mirage owners a lot of grief (and cash) in the future if they don't have to swap out their heater core. I will be doing this to my own car when it gets warmer.

    __________________________________________ click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 52.2 mpg (US) ... 22.2 km/L ... 4.5 L/100 km ... 62.6 mpg (Imp)

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  5. 02-21-2021, 07:49 PM #4 foama
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    Quote Originally Posted by Top_Fuel View Post That's great news, foama! This is going to save Mirage owners a lot of grief (and cash) in the future if they don't have to swap out their heater core. I will be doing this to my own car when it gets warmer. I think it would be very worthwhile to flush out the OEM coolant and replace it asap before things worsen. Never mix different brands of coolant, and make certain you are adding the correct stuff.
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  7. 02-21-2021, 10:19 PM #5 Eggman
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    Good write-up foama - simple and cheap. Makes me wonder what the throttle body heater circuit looks like.
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    __________________________________________ click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)

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  8. 02-21-2021, 11:47 PM #6 MetroMPG
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    Thanks, foama!
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    __________________________________________ click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 61.4 mpg (US) ... 26.1 km/L ... 3.8 L/100 km ... 73.7 mpg (Imp)

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  9. 02-25-2021, 06:36 PM #7 foama
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    Quote Originally Posted by Eggman View Post ... Makes me wonder what the throttle body heater circuit looks like. Took the throttle body off today, and there was nill restriction or goo or anything. The water in and outlet is a 6mm tube, only about 2cm or 1 inch long inside the throttle body. I think we don't need to worry here.
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