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  1. #1

    92 sl650 base gasket leak question

    So I had the pto base gasket blow outside under the the exhaust and I replaced it, found out later that the thermostat was plugged. At the time I thought that this was the cause of the failure because it blew at the weakest point because of the blockage and the temp alarm was going off. However I replaced the gasket and gutted the thermostat, I went out today and sure enough the same base gasket blew in the same place.... does anybody have any ideas what keeps causing this? The temp alarm didn't go off so I don't think there is a blockage anymore but does anybody have any experience or advice?

  2. #2
    Can someone help clarify my understanding of the cooling process in Polaris PWC? Is the thermostat at the beginning or end of the cooling process. For some reason I conceptualized it being at the end, which in this case, if it was plugged, it would of had no impact on the first time my base gasket blew with a leak because no water would of made it there. Does anybody think I may have a blockage in the lower-end of the case which is causing this leak? Have the cylinder all apart and this is no sand in that, any advice??

  3. #3
    Click avatar for tech links/info K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada

    Arrow Water cooling flow circuit, Polaris 2-stroke personal watercraft

    The following is a general overview of the water cooling flow.

    Note: The very early 1992 and 1993 Fuji engines have an additional cooling water flow through the engine crank case.

    When the watercraft is floating in water and the engine is running, there is a high pressure water stream at the exit of the jet pump, even at idle speed.

    Inside the jet pump exit nozzle (which is not the steering nozzle) there is a small plastic mesh screen, about the size of a postage stamp. It is located on the right side of the exit nozzle taper. You can feel it with your fingers, but would need a small mirror and flashlight to actually see it.

    The plastic intake mesh screen must be kept clean and free of clogs.

    Directly outside and to the right of the mesh screen is a cast fitting on the exit nozzle, internally open to the mesh screen cavity. Fitted into this is the water tube, which runs forward from the jet pump and passes into the hull.

    The water tube may be made of plastic or metal. It enters the hull via a hole in the base of the jet pump. Where the water tube passes through the pump base it must be sealed with sealant to prevent water seepage into the hull.

    It is important that sealant not get inside the water tube when the tube is being installed.

    The pressurized water from the jet pump flows forward through the water tube and arrives inside the hull at a nipple, located down low on the right side of the jet pump. All left-right perspectives are from standing behind the watercraft.

    A 3/4" hose connects from the water tube supply nipple and feeds the engine.

    First the cooling water flows into the water jacket of the exhaust pipe and exhaust manifold. From there the water flows around the exhaust ports and into the individual cylinder water jackets, then up into the cylinder heads.

    From the cylinder heads the water flows up into the water manifold (water bar) and towards the thermostat housing.

    Inside the thermostat housing is the thermostat itself and also a spring loaded pressure bypass valve. Water flows through the thermostat housing and out the exit hose towards the rear of the hull.

    Every engine also has a fitting for directly injecting a small stream of water into the interior of the exhaust pipe to cool the exhaust gases as they flow towards the water box. Configuration varies depending on the engine and the model. A typical red domestic engine will have a small diameter water hose that links between a metal mesh filter screen fitting and the actual water injection orifice. Both the orifice and the mesh screen must be kept clean to avoid melting the rubber exhaust hoses and plastic resonators.

    Related info; How to properly flush your 1992 or 1993 Polaris PWC

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