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Thread: CSI: rear wheel arch rust. Seal these fasteners!

  1. #1

    Exclamation CSI: rear wheel arch rust. Seal these fasteners!

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    This is my third 2014 Mirage. All three of them had evidence of rusting from the inside out in this area (both sides), though this one is the worst by far.

    I know other members are starting to see the same thing. (Obviously worse in locations that use salt on the roads or have salt in the air.)

    I spent some time investigating how water is getting inside to cause this rust, and I think I know what's going on.


    It's a water trap...

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    The area in question is a cavity formed between the outer wheel arch sheet metal and the inner wheel well structure, joined at the wheel arch flange. The gap between them where the rust happens is only about 4-5 mm, or 1/4 inch.

    If & when water gets into this cavity, it can potentially fill up to the blue line before spilling forward, down the forward part of the wheel arch, and out the existing factory drain holes in the rocker panel structure.

    But water below that line will just sit there, contributing to corrosion, until it eventually evaporates. Eventually, as with my car, corrosion will perforate the metal, blister the paint, and then the water can weep directly to the outside.

    I suspect all Mirages that don't live in arid climates probably have water sitting in this cavity from time to time. If you also happen to live where there's salt in the air or on the roads, of course that's a bigger problem.


    How is water getting inside?

    First guess:
    I figured the problem was poor sealing or a gap somewhere along the wheel arch / wheel well flange that was letting in spray from the tire. But after repeatedly filling the inside of the wheel arch with water, watching for seepage, I couldn't find anything. The water only came out the rocker panel drains.

    Second guess: there are four fasteners that penetrate the cavity from the outside that could potentially let moisture in.

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    Two (circled area on the right, fasteners not shown) are for attaching the bumper cover. The other two are behind the tail light assembly, to hold it in position on the body (one is shown by the arrow).

    Primary suspect:

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    For some reason Mitsu put a foam gasket on this tail light locating fastener, but not on the other one.

    Hmm! Do you think maybe they discovered water ingress was a problem here??

    Sure enough, when I squirted around this fastener with low pressure, low volume water (squirt gun), some of it eventually wicked past the gasket to the inside of the cavity where it could drip and/or run straight down and replenish the swimming pool.

    Note: the tail light does NOT sit flush against the body. Water running down or along the side of the car can easily reach that fastener.

    I wonder how much water could seep in during an all day rain? Or at a high-pressure car wash? Or blasting down a wet, salt-soaked highway?


    Solution...

    Even though I think the top fastener is the most likely culprit (so did Mitsubishi, obviousy), I would seal around all four fastners with silicone.

    Then I would get some anti-rust spray into that cavity (ideally when you know it's dry).


    Accessing the cavity...


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    I didn't pull the left side cover, but the right side is accessible behind the side panel of the cargo compartment. You won't be able to get your fingers down into the narrow cavity to check for water. I used strips of paper towel to "dip" it dry.


    Cold weather complication...

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    If you live where water freezes in the winter, it gets more complicated.

    Water expands as it freezes, and the pressure may have caused the bead of sealant on the wheel arch flange to tear neatly along this line (frozen sealant won't flex under tension, it'll just break). Corrosion between the two sheets of metal would also put pressure on it.

    Either way, that split has just created more opportunity for salty water to get in and accelerate the damage.

    Q.E.D.!


        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


  2. The Following 5 Users Say Thank You to MetroMPG For This Useful Post:

    BigMW (11-25-2022),Cobrajet (07-09-2021),foama (11-25-2022),george (07-09-2021),Wil B (07-09-2021)

  3. #2

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


  4. #3
    Senior Member dspace9's Avatar
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    Hey MetroMPG how does the car look underneath?

        __________________________________________

        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)


  5. #4
    Not terrible - no gaping holes yet! But you can tell it's never been rust-proofed.

    You've had yours Krowned right? I wonder if they got inside this wheel well cavity.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


  6. #5
    Senior Member dspace9's Avatar
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    Quote Originally Posted by MetroMPG View Post

    You've had yours Krowned right? I wonder if they got inside this wheel well cavity.
    Yep krowned every year, going for my 7th or 8th krown in august. I have no rust at all around the wheel wells, but I see that one spot there.. I'm getting rust too.

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    Take a look up from the rear license plate, where the lights for the plate is. That spot rusts bad on the first Mirages. Worst spot on my car for sure. You don't see it however.

        __________________________________________

        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)


  7. #6
    Did they drill a hole to spray inside your rear wheel well cavity? If they did you'll find a black plastic plug covering the hole, somewhere around here:

    Name:  krown-hole.JPG
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        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


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    dspace9 (07-08-2021)

  9. #7
    Senior Member dspace9's Avatar
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    Just looked, no plugs in the wheel wells, a la like they have the plugs on the doors etc.

    That link there doesn't work lol

    I'm happy with Krown, but I think it basically prolongs life of the car; not preservse the car, like a perfect museum piece.

    For that, you have to park the car all winter long. Or buy a car from the South.

    Still, my doors etc look perfect, my Mirage looks basically brand new still. In that sense krown has been worth the money. No surface rust on the body.

        __________________________________________

        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)


  10. #8
    Administrator Daox's Avatar
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    Just looked and I have the slightest spec of rust on mine, but only on the passenger side.

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    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


  11. #9
    Tim, yeah not horrible. That's basically what my second Mirage looks like:

    Name:  rust-rr-wheel-arch.jpg
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    Keep in mind, it's worse than it looks because it's coming from the inside out. Gotta seal the leaks, dry it out & fill that cavity with something to stop the cancer.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


  12. #10
    Quote Originally Posted by dspace9 View Post
    Just looked, no plugs in the wheel wells, a la like they have the plugs on the doors etc.

    That link there doesn't work lol
    Reposted. Do you see it now?

    So no rust on the bottoms of your doors? My white car doors are all rusty where the outer skin is folded over and sealed to the inner structure. Again, an inside out rust process. That's one of the easiest rust spots to prevent since you can just spray oil in through the existing drain holes in the bottoms of the doors.


        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


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