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  1. #1

    Reasons for rupturing hose between waterbox mufflers

    Hi Guys,

    Completely new to the forum and also completely new to kawasaki skis. I just recently purchased a used but (supposedly) low hours STX-12F and I had it out on the water this weekend and it ruptured the first hose that crosses over between the right and left water box mufflers. The rupture looks to be caused by excessive heat. The rubber was very brittle and bubbled and the end result is a 2 inch rupture in the hose. After inspecting the second hose that crosses over back to the exhaust outlet I noticed that it was also very brittle and probably wasn't very far away from failing also. And if that wasn't enough I also noticed that the large plastic ducts that run up the holes coming through the plastic on the back seat platform had holes melted in them from resting against the rubber exhaust hoses.

    I don't know much about how the exhaust system is supposed to operate but I am pretty sure that the exhaust should be cooled down by the water in the mufflers and the rubber cross-over hoses between the mufflers should never get that hot. So here are my questions:

    1. When I hook up a garden hose to the flush attachment and run the jetski should there be water in the waterbox mufflers? Also, should there be water coming out of the exhaust outlet?

    2. I am thinking that the lack of cooling is caused by a plugged cooling line somewhere in the ski. I have the factory service manual, so I can see where all the cooling hoses run, but which of the cooling lines is used primarily to cool the exhaust gases?

    3. When I attach a hose to the flush attachment I get water flowing through the black nipple at the front right of the ski and through the hose outlet that exits just above the steering nozzle at the back of the ski. So doesn't this mean that my cooling lines are clear? Or is it still possible that one of the lines may be clogged?

    Sorry for the long winded question but I just wanted to get all the information out there for anyone who can help me.

    One more thing to note, this is the first time I have ever had the ski out and I had it out for about 20 minutes before the hose blew and I never got any warnings about oil or water overtemp. So I think the motor cooling part of the cooling circuit is working.

  2. #2
    btldigger's Avatar
    Join Date
    Feb 2007
    lebanon tn.
    Somewhere along the exhaust system you should have a point where it injects water into the exhaust. If that gets clogged then you overheat the rubber hoses and they fail. If its running on the hose you should see water comming out the exhasut outlet.

  3. #3
    So while I was waiting for the parts to come in I did some more investigating and looked for hose blockages. I couldn't find hoses with blockages in them, when the flush fitting was hooked up. When I took the hoses off they all seemed to have water flowing through them. Also, while running the ski on the hose and watching the outlet of the left waterbox muffler I noticed that there is some water coming through the outlet that leads over to the right waterbox muffler. It didn't seem like alot of water though, it was like a gentle spray of water, it was enough water to make my hand wet if I put it infront, but not alot.

    Now I have a couple questions:

    1. How much water am I supposed to see coming through there, is what I am seeing normal?

    2. Does the cooling water for the mufflers come through the colar just before the right waterbox muffler? (I have it highlighted in the red square on the attached picture)

    Any help would be appreciated.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #4
    I don't have any water at all coming out of my hoses on the port or starbord sides. Is this water remaining in the hull? And yes you should see water out of the exhaust when on the hose. Also it is suppose to build up some pressure and spit out of the exhaust.

  5. #5
    So I installed new hoses to replace the ruptured ones and I am still getting only a very very small amount of water exiting through the exhaust while running on the hose. The only way you can even tell water is coming out of the exhaust is by putting your hand infront of the exhaust and your hand will get a little wet. I am assuming that more water than this is supposed to come out. I ran the ski on the hose for about 5 or 10 minutes and the waterbox mufflers were hot to the touch and I don't think that they should be.

    Can anyone else with a stx kawaski let me know how much water I am supposed to see coming out of the exhaust?

    Also, can anyone explain to me the route that the water takes to flow into the exhaust. Is it possible that the sleeve just before the first waterbox muffler is clogged so that it still allows water to flow up and through it, but not into the muffler?

    I am really depserate to figure this thing out and get my ski going again, so any help would be great. Thanks alot guys.

  6. #6
    mirror's Avatar
    Join Date
    Jan 2006
    Seminole, FL
    What year do you have? There is a problem with some of the older years under the intake manifold is a piece of crap pot metal tube that has two inlets into the block and one bib pointed towards the rear for a hose to connect to. This will completely disentegrate and block the cooling line. Not sure if that is what you have since they have fixed this with the newer models. Feel under the intake manifold and see if it is two fittings or just one long tube about 3/4" in diameter and 5" long. If that latter is what you have then you need to determine if it has a copper fitting where the hose goes or else the worst case is the pot metal continues to where the hose attaches and that is what corrodes. Long post but hope it helps.

  7. #7
    It is a 2007, I think they fixed the problem for that model year. But I will check what is on there anyways just to make sure.

  8. #8
    I have two 2005 STX 12-f 's and both spit water out of the exhaust enough to saturate your hand when on the hose and the peeing port on the side has a steady stream coming out of it. Sounds like yours has insufficient water flow. My problem with overheating turned out to be the temp sensor. I am not sure why it affected the flow of water but when the shop replaced it that solved my problem. Hope that helps

  9. #9
    I think I found my problem. I took off the hoses to and from the sleeve/fitting just infront of the left waterbox muffler and found that there is sufficient waterflow through both of those hoses. So then I blocked off one port and poured water in the other and found that water was not emptying out of the sleeve and into the exhaust. So I am thinking that there is a blockage in that sleeve somewhere. I am going to try and take out the waterbox muffler tomorrow and see if I can clear the blockage.

    I really hope this fixes mu problem. I will let you guys know how it turns out.

  10. #10
    Well as far as I can tell the problem is fixed! I took the waterbox muffler out and flushed and cleaned out the the cooling water passages as good as I could. Some really strong drain cleaner is what seemed to really clean it out the best, after a couple treatments of that, the water flowed into the muffer alot better than it had before.

    I took it to the lake this weekend and spent a whole day on the water and burnt a tank of fuel with no problems and the exhaust system seems to be staying much cooler now.

    Thanks for all the helps guys!

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