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Thread: Why does my radiator keep leaking?

  1. #1
    Join Date
    Jul 2019
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    Bellingham
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    1995 BMW M3 Coupe

    Why does my radiator keep leaking?

    So I've been going through radiators lately (Mishimoto all aluminum rad specifcally) , approx 1/year. Every one has ended up failing where the tubes meet the end tanks on the top half of the radiator. Anyone else experienced this issue with Mishimoto's? Or why else would they keep failing in the same spot? I can't imagine they would ALL have manufacturing defects...but maybe? Running a 95' M3 w/ S50.

    I replaced the head gasket about 18k miles ago, new oem water pump, new expansion tank cap, fresh coolant (blue pentofrost nf mixed 50/50), oem thermostat housing with new gaskets and I've had no issues with overheating.

    Any ideas would be much appreciated!
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  2. #2
    Join Date
    Oct 2003
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    Seattle
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    99 M3

    Why does my radiator keep leaking?

    I think Mishimoto has “Lifetime Warranty”.

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    Last edited by bluptgm3; 09-22-2020 at 12:33 AM.

  3. #3
    Join Date
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    I wouldn’t rule out a bad headgasket job, especially if you used a Victor Reinz which are known to be shit. Mishimoto rads are also in that shit list.

    Might be time for a pressure test on the head work. If that passes, switch to an OE BEHR/Mahle Z3M radiator.

  4. #4
    Join Date
    Jul 2019
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    1995 BMW M3 Coupe
    Quote Originally Posted by Braymond141 View Post
    I wouldn’t rule out a bad headgasket job, especially if you used a Victor Reinz which are known to be shit. Mishimoto rads are also in that shit list.

    Might be time for a pressure test on the head work. If that passes, switch to an OE BEHR/Mahle Z3M radiator.
    When I installed the last radiator (post head gasket) I had the system pressure tested and everything came back good.

    I’ve been thinking about switching back to OE, I just keep hoping that one of these Mishimotos will work..

  5. #5
    Join Date
    Jun 2005
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    New England
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    25,402
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    F90 M5; E36 M3 Turbo
    The Behr stock and Z3M radiators are good and the price has come way down on the Z3M version. I have run both without issue. For at least 5 years, I have run the Mishimoto xline Z3M without issue, but I do occasionally read about people suffering failures. These motors can run pretty high coolant pressure. I think the stock 2.0 bar cap allows up to 29psi. I use Evans coolant, a heavier duty Stewart pump that may work better for the thicker coolant, and a low pressure cap (I think it is 1.2 bar) that I run loose for little to no pressure.

    Certainly a failing HG that pressurizes the cooling system will stress the radiator.

  6. #6
    Join Date
    Oct 2009
    Location
    Dublin, OH
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    7,886
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    '95 M3, '17 Civic Si
    your cap might have failed and is allowing too high pressure. But it's more likely that your Mishimoto is just doing Mishimoto things and is just crappy inherently.

    Replace your rad cap with a brand new OE one and switch to a stock radiator or higher quality one (PWR, Zionsville, Koyorad, etc)
    Last edited by das borgen; 09-23-2020 at 12:23 PM.
    -Rich-


  7. #7
    Join Date
    Jul 2019
    Location
    Bellingham
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    My Cars
    1995 BMW M3 Coupe
    New oem cap is currently on there. I'm getting a warranty radiator from Mishimoto but I'm going to switch to a mahle-behr this round and hope it holds up longer. I'll get it pressure tested afterwards to be sure its not another head gasket and post an update when I know!

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