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  1. #1

    MSX 150 overheating, incorrect thermostat, coolant hoses dumping coolant

    Hi, new to both this forum, and jetskis too. I have no knowledge of them at all, so a little help is needed.

    I recently bought two 2004 MSX 150's, both with overheating problems. I'm dealing with them one at a time, in the hope that what I learn from the first, might help with the second.

    I now know the one I am working on has a stuck closed thermostat, and the other an incorrect thermostat, with no poppet, and so I am replacing both with the correct ones, which has a poppet.

    But to deal with the first one, when it overheats it goes into limp mode, and when I inspect it, I find hoses have been blown off the enclosed cooling system, and all the coolant has been lost. (this has happened twice). I don't know if this is happening before or after limp mode, but my question is, why would this happen at all, is there anything other than the expansion tank to prevent this?

    Hopefully, Les


  2. #2
    ripcuda's Avatar
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    Welcome to GH!

    Which hose is blowing off and releasing the coolant from the closed-loop cooling system? One on the heat exchanger (big round thing under the intake manifold)?

    Bad overheating on the Weber (the engine in you ski is made by Weber)... can cause lots of issues. A warped block being the worst. You *really* need to perform a reliable compression test on the engine. It's also very possible (I dare say likely) you blew the head-gasket and that is also pressurizing the coolant system.

    Do you have any oil slick in the coolant... as would be seen floating on top the coolant in the reservoir?
    Do you have milky/foaming oil... as would be seen on the oil tank dipstick?
    What are you compression #'s?
    When idling... do you see a steady stream of coolant whizzing into the coolant reservoir from the small hose?

    Cheers!

  3. #3
    Thanks, all good info. First, the hose that blew off twice, IS a big one on the left of the ski I'm not near it to check right now, is that the intake side?
    to deal with your points-

    I don't know if there is an oil slick in the coolant, I've lost it all within a few minutes both times, but I will look for it in future.
    No milky, foaming oil noticed, during idling with flush kit, but not really checked with hot engine.
    Already done a compression test, 115 and 95. only changed a couple of pounds when I added oil in cylinders.
    Steady stream of coolant to the tank.
    I also did a 15lb. pressure test on the coolant, no obvious loss of pressure over half hour.

    Les

    Les

  4. #4
    ripcuda's Avatar
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    Those compression #'s spell doom. That engine is going to need a rebuild. It's possible you have a blown headgasket (which you have to pull engine to replace)... but if the coolant system is holding pressure... I'm doubting. Seems more likely the engine has failed Nikasil plating in the cylinders... which would require a pull and full rebuild with reconditioned block.

    So I don't think the coolant system is your biggest issue at this point.

    How is the 2nd MSX? Same there?

    Cheers!

  5. #5
    (So I don't think the coolant system is your biggest issue at this point.

    How is the 2nd MSX? Same there?)

    Well, you haven't surprised me, I had half been expecting to have to remove the engine at some point, based on the compression readings, but your suspicion of a blown head gasket gave me hope that the low readings could be attributed to that, and it would explain the blown hose too. It looks like I might as well start pulling the engine.
    Thanks for the help so far, but I have a feeling I will be on the site again in the near future.

    Les

  6. #6
    "(So I don't think the coolant system is your biggest issue at this point.

    How is the 2nd MSX? Same there?)"

    Engine out, head off. Apart from leaking valves, looks good, but I need to be sure I resolve the pressure issue while I have the engine out. Even if the hoses popping off is being caused by a leaking head gasket into the coolant, can anyone advise wether or not there is some kind of pressure safety valve in the system? The expansion tank cap looks a little complicated, does it act as a safety valve?

    Les

  7. #7
    ripcuda's Avatar
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    There is no safety valve on the coolant system. Normal operating... the coolant system will see a pressure of around 1bar (14psi) max.

    So no cracks (catch a fingernail on) or flaking of Nikasil in the cylinders? Your comp #'s sounded like it could have been that. So tight valve-to-shim clearances causing valves to hang open?? Or just bad valve seats causing bad seals?

    Could you see on the headgasket where it might have been blown?

    Cheers!
    Last edited by ripcuda; 09-28-2016 at 10:45 AM. Reason: learned something new

  8. #8
    Kosh's Avatar
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    The MSX150 coolant cap has a built in pressure relief valve, it doesn't have the tradional overflow pipe it releives around the outside of the cap.

    Easy enough to test by hooking up a bike pump.

  9. #9
    Moderator HiPeRcO's Avatar
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    Quote Originally Posted by dunromin View Post
    Thanks, all good info. First, the hose that blew off twice, IS a big one on the left of the ski I'm not near it to check right now, is that the intake side?
    It sounds like you are referring to the air hose that runs from the turbo to the intercooler. This hose has a lot of air pressure when the turbo is making boost, and it will pop off if not tightened properly. This is almost certainly not related to your coolant issue.

  10. #10
    ripcuda's Avatar
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    Quote Originally Posted by Kosh View Post
    The MSX150 coolant cap has a built in pressure relief valve, it doesn't have the tradional overflow pipe it releives around the outside of the cap.

    Easy enough to test by hooking up a bike pump.
    Thanks Kosh! I didn't know that... makes sense the system would have some sort of relief though.

    Cheers!

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