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Thread: Heater core fix attempt, advice?

  1. #1
    Member pawpaw's Avatar
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    Heater core fix attempt, advice?

    I will try to keep this brief as I am low on time at the moment.

    My 2014 Mirage lost most of its heat output this winter which led me to joining this forum after lurking for years. I had an attempt at fixing the problem with only partial success and I think there may be a deeper issue with my cooling system.

    Before the fix attempt I measured almost 150 F at the leftmost vent and only 70F at the rightmost with auto climate set to 89, outside air, and upper vents only.

    I admit I hadn't paid much attention to the cooling system on the Mirage. This is not something that usually needs attention on new cars so I was lax. After noticing the heat issue I also noticed the coolant was at the low mark in the reservoir and when I took off the cap the coolant was not at the level of the cap and there were some whitish deposits under the cap.

    I drained the coolant. It looked like brown crap. This may have been partially due to a topup with pink coolant that I had on hand a year or three earlier. (trivia, this was still the correct coolant for the car just the wrong color, there are red and blue asian coolants that are basically the same except for the dye and our Corolla took red)

    I did a bunch of drain and fill cycles with distilled water and tried both the zerex and the prestone coolant system flush and cleaners.

    Somewhere in there I backflushed the heater core and some white crystalline stuff came out.

    After what seemed like 20 drains and fills with distilled water (I lost count) I topped the system up. I used Recochem OEM blue concentrate antifreeze to get about 60% concentration. The block drain was never touched due to the hassle factor while lots of radiator drains and fills was easy if tedious.

    My heat output has improved after all of this. I usually get high 90's to 110 or so at the right vent now. This seems only partial success but it is good enough that I wonder if it was ever much better. If not for other worries I might be tempted to just live with this and start yearly drains and fills with 50/50 coolant (Zerex blue asian probably).

    The other worry is that I have a leak or something somewhere that caused this problem in the first place. So far I have replaced the radiator cap twice (with new aftermarket caps!) but every time I remove the radiator cap cold the coolant level has dropped completely out of the neck of the radiator. I can't recall seeing this on other cars (I checked our 2006 Corolla when my son was home and the coolant still looked good and was at the level of the radiator cap, same with our 2014 Accord).

    Any ideas what is going on here or does this seem normal (coolant level keeps dropping below cap level and coolant looked trashed on a relatively new car)?

    I'm still debating taking the car to the dealer but you can see the lengths I will go to avoid that particular torture...


    Last edited by pawpaw; 12-15-2019 at 08:05 PM.

  2. #2
    Senior Member Top_Fuel's Avatar
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    Before the fix attempt I measured almost 150 F at the leftmost vent and only 70F at the rightmost with auto climate set to 89, outside air, and upper vents only.
    If you are not aware, there is a definite issue with the factory heater cores in 2014-2015 Mirages becoming internally restricted. This restriction primarily affects the passenger side of the heater core. The main symptom is that the driver's side vents blow hot/warm air while the passenger side vents blow warm/cool air (the EXACT symptoms you are seeing). You can read more about the issue here.

    That's great that you got positive results by back-flushing. It sounds like your cooling system was somewhat neglected...or possibly that the wrong coolant was used to top off your system at some point in the past. I don't think anyone has flushed their cooling system and described the old coolant as "brown crap" lol.

    If you install a brand new heater core in a Mirage, you will see vent temperatures approaching 150 degrees across ALL of the dash vents. So while your heat has gotten better, there's probably still some of that mystery goo that has collected on the passenger side of the core. Nobody has come up with a magic fix for that yet.

    My own car is like this. You can read my story here. My heat is not perfect but its fine 99% of the year. Do I pull my dash apart to fix a problem like that? I'm not ready to go there just yet. But I don't live where it gets really cold in the winter, either.


        __________________________________________

        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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