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  1. #1

    Water on while engine off - What not to do vs why?

    I see a lot of no-no's about turning the water hose on while having the engine off but I dont exactly understand why not.

    I did a search but all I found was "Dont do it".

    I dont understand because shouldnt the water jackets all be sealed off from the air supply? If the water jacket does leak; shouldnt it be fixed rather than just avoided?

    Please help me make sense of it. I've been turning the water on for 20~30 seconds before starting the engine thinking that the engine needs the cooling jackets filled before starting it.

  2. #2
    Gus13letter's Avatar
    Join Date
    Apr 2008
    Tampa Bay, FL
    Always start the ski before the water!
    You will hydro-lock your engine by supplying the ski with water before starting the ski. By supplying the ski with water before starting it, allows the waterbox to fill up with water and back-flow into the engine cylinders filling the engine with water! When the engine is on the exhaust pushes the water out of the waterbox, not allowing this to happen. You can safely start jetskis out of the water and safely allow them to run for 30-60 seconds without a problem.

    On boats it is completely the apposite!! Start the water flow to the engine and then start the engine.

    I cant tell you of how many skis I have heard of which were brand new and were destroyed because they thought the process was like a boat and the dealers didnt tell them otherwise.

    Hope this helps.

  3. +1 by:

  4. #3
    The waterbox; is the tail piece after the stinger right? Under the battery box? Kinda looks like a Honda Civic rice/fart can? Or is it the "Water tank" after the metal can just before the exhaust exit?

    Strange how the design requires exhaust to push the water out. Isnt that creating more backpressure and less performance? Why is it like this other than for what.... sound deadening? Can this be modified for more power/flow?

    So what Ive been doing; I hope wasnt too bad for it. The waterbox is pretty low in the hull so I hope it didnt ever get the chance to fill up to the engine in 20~30 seconds. I presume if the water fills it would backtrace 'up' through the stinger, around to the exhaust manifold, flow past the PVs, and into the cylynder/crank. Correct?

  5. #4
    jstanfi1's Avatar
    Join Date
    Apr 2013
    Lafayette, Indiana
    As a long time boater I made this mistake. Wound up with water in the crankcase, ugh. The issue is gravity more than anything...these two stroke engines don't have the same kind of cooling jacket as what you're thinking of for a car, etc., and they're not sealed off from the rest of the engine. The pressure on a garden hose is sufficient to backup when the impeller isn't running and creating the pressure differential necessary to "pull" the water out of the jacket.

    If you've been running water for 20-30 seconds first, there's a chance you have put water in the crankcase. There are lots of threads on getting water out of the crankcase, but to check I would pull the plugs and crank (with the plugs grounded or while holding the stop button at the same time) and see if water comes out of the plug holes. And I'd probably go ahead and run some Seafoam through it too as a preventive measure to dry up whatever water might be down there. Good luck!

  6. #5
    mudslanger's Avatar
    Join Date
    Jul 2010
    Huntsville Al
    Just to add to what gus said the water will flow back to the engine. if you pull the battery box off and look back there the exhaust system is designed to not let water come in through the exhaust wile sitting on the river,lake ocean. the exhaust is actually higher than the highest part of the engine on most all PWC in the rear of the ski. hope this helps you understand how it works.

  7. #6
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    The exhaust is water jacketed until the end of the stinger, where the water jacket is open to the remaining parts of the exhaust system. That water supply cools the water box, rubber exhaust hose, and rubber couplings between. If you look at a your ski or parts diagram, you'll see after the water box the exhaust hose goes up over to the other side. That up loop keeps water off of the exhaust when you sitting around and it also creates a situation where running on the hose can fill up the waterbox and backfill through the stinger and down into the exhaust manifold and into the engine.

    its hard to explain and easier to understand if you had the exhaust apart to look at it.

  8. #7

    Join Date
    Aug 2006
    Another point: cold 2 strokes like the GPR can run without water for 45-60 seconds without problem. 4 strokes heat up way quicker.

  9. #8
    Pistonwash's Avatar
    Join Date
    Aug 2005
    Don't ever do it again if you don't want to seize your want the science of it, look at how the exhaust works with water injecting into it. But, DO NOT TURN THE WATER ON WITH THE ENGINE OFF, you will seize your engine. Period.

  10. #9
    The exhaust is water jacketed until the end of the stinger, where the water jacket is open to the remaining parts of the exhaust system.
    I follow this explanation.

    OK guys, got it. I had the stinger off last night to install my carb T-Handles and saw the flow of it all. Hopefully the seconds of engine-off water-on only filled up the waterbox and part of the stinger as that stuff is low and downstream. I also found no evidence of water at a high level or under the spark plugs.

    I picked up an easy on-off valve for my gardenhose today. It should make water on/off right at the ski much easier than running back and forth to the side of my house on a 100 foot hose.

  11. #10
    VdeKock's Avatar
    Join Date
    Nov 2012
    The Netherlands
    Off topic,

    But how long can you run the engine on the hose when you have the jetworks mod??

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