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Thread: Is this normal? (Coolant on top of expansion tank cap)

  1. #1
    E500E Guru 500ESpain's Avatar
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    Is this normal? (Coolant on top of expansion tank cap)

    Hi,

    As you may know, I've been having some overheating issues. So far I've replaced the thermostat, radiator (broken) and viscous fan. The car still overheats, going way beyond the 100 degree mark in normal driving conditions and mild temperatures. My main suspect is a defective viscous fan (new Sachs unit). I never hear it and I thought it was normal until I drive a friend's E500 and I could clearly hear it.

    Anyway, I haven't had the time yet to deal with it but in the meantime I thought a new radiator cap would not hurt. I went out for a short drive yesterday and when I came back I found that on the cap. Engine temperature was high but not crazy high, just over the 100 degree mark and auxiliary fans just kicked in.

    Defective cap? Too much pressure in the system? Coolant too hot?

    Thanks in advance for your help, as always.
    Attached Images Attached Images
    Esteban

    1971 Seat 600E, 1981 Mercedes 300TD, 1984 Mercedes 300D, 1992 Mercedes 500E, 1995 Range Rover 4.6 HSE, 2005 Audi A4 2.5TDI Avant, 2007 Triumph Bonneville

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  3. #2
    .036 Hoonigan™
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    Re: Is this normal?

    [QUOTE=500ESpain;148174] As you may know, I've been having some overheating issues. So far I've replaced the thermostat, radiator (broken) and viscous fan. The car still overheats, going way beyond the 100 degree mark in normal driving conditions and mild temperatures. My main suspect is a defective viscous fan (new Sachs unit). I never hear it and I thought it was normal until I drive a friend's E500 and I could clearly hear it.
    Sounds like the new Sachs clutch is not calibrated properly - very common issue, unfortunately, as Klink and others have described in detail in other threads. For a quick test, pull the 2-pin connector at the front of the intake manifold, this should trigger the twin electric fans on high speed. Go for a test drive and see if the temp stays at 100C or below. If so... the fan clutch is likely the main problem.


    Quote Originally Posted by 500ESpain View Post
    ... I thought a new radiator cap would not hurt. I went out for a short drive yesterday and when I came back I found that on the cap. Engine temperature was high but not crazy high, just over the 100 degree mark and auxiliary fans just kicked in. Defective cap? Too much pressure in the system? Coolant too hot?
    Never seen that before, but it does appear to be a defective cap. Weeeird. If pressure in the system exceeds the cap rating (1.4 bar?) it should divert coolant out the overflow hose to the overflow tank inside the fender. You should never have coolant anywhere around the cap or expansion tank

    Dave M.
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  5. #3
    E500E Guru Melville's Avatar
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    Re: Is this normal? (Coolant on top of expansion tank cap)

    I think I might have the same cap issue. I was losing a little bit of coolant, and I could see residue and liquid around the expansion tank, as high up as the cap. I just pressure tested the system and the area around the expansion tank was bone dry. The only component that is different during regular driving vs. pressure testing is the cap. My cap is pretty new so I'll try to put on my old cap to see if the leak from that area goes away.

    Another fact which may or may not be relevant -- recently the coolant level rises quite a bit above the seam after I've gone for a drive. A good inch or so. I don't recall this happening until recently.

    Also possibly relevant, recently these parts have been changed: coolant level sensor, radiator, t-stat, pretty much all hoses, water pump, aux fans and fan clutch.

    I also found the leak in the picture below. How tight should the clamp be? I gave it close to a turn more and it didn't feel very stiff. I don't want to over-tighten (if that's possible).

    IMG_5244.JPG

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    E500E Guru nocfn's Avatar
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    Re: Is this normal? (Coolant on top of expansion tank cap)

    Clamp it to stop leak. Did you place tstat?
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    E500E Guru Melville's Avatar
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    Re: Is this normal? (Coolant on top of expansion tank cap)

    Yup, t-stat replaced.

    I pressure tested again after slight tightening of the clamp and no more leak. I took it to just under 15 psi and left it for a few minutes. Is it safe to assume that, at this pressure and after a few minutes, if there were still a leak it would show up?

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    .036 Hoonigan™
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    Re: Is this normal? (Coolant on top of expansion tank cap)

    Quote Originally Posted by Melville View Post
    Yup, t-stat replaced. I pressure tested again after slight tightening of the clamp and no more leak. I took it to just under 15 psi and left it for a few minutes. Is it safe to assume that, at this pressure and after a few minutes, if there were still a leak it would show up?
    The pressure tester is your friend for small leaks like this. If it holds 15psi and there's no more leak, I'd call it good.

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  11. #7
    E500E Guru 500ESpain's Avatar
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    Re: Is this normal? (Coolant on top of expansion tank cap)

    I've put back the old original cap and just by hand you can feel that the spring on the Mercedes one is much stronger. Both are supposed to have the same pressure rating.

    The defective brand new one is a Metzger.
    Esteban

    1971 Seat 600E, 1981 Mercedes 300TD, 1984 Mercedes 300D, 1992 Mercedes 500E, 1995 Range Rover 4.6 HSE, 2005 Audi A4 2.5TDI Avant, 2007 Triumph Bonneville

  12. #8
    .036 Hoonigan™
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    Re: Is this normal? (Coolant on top of expansion tank cap)

    Best to only use the OE or OEM (Reutter) caps. They are under $10 USD last I checked.


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