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  1. #1

    01 GTX 787 RFI Overheating

    Starts, runs, and drives great for 2-3 minutes when on the lake then overheats. Has great compression on both sides. I took off all the coolant hoses and blew air threw them, didn't seem to find any obstructions. Took the impeller off and nothing plugged, the rubber washers were intact between the impeller and the hull. While in the water I started the machine and took the water outlet hose on the head off (towards the back of the ski) and there is no water coming out at all. I put my finger over the port on the head and could not feel any pressure at all. I also seemed to have melted the rubber hoses on the exhaust which I recently replaced because the old ones were brittle.

    Couple questions, is the prop solely responsible for pushing water thru the two small ports in the impeller housing and into the inlet hose that feeds the head and also tee's off to the water flow regular? Or does the engine create some suction, or both? Also is the water flow regulator just responsible for cooling the exhaust or does it tie into the flow of the whole system?

    I am curious if I have an issue with the water flow regulator, bad head gasket, or ????

    Appreciate any feedback!

  2. #2

    Join Date
    May 2007
    Minneapolis MN

    I just diagnosed a similar problem on my RFI except my engine wasn't overheating but the rubber hose that connects the tuned pipe to the water box (muffler) burned through. To answer your question about how water gets into the system, there is no pump of any kind and water is supplied through the ports in the jet pump by the pressure developed in it. The supply line connects to the head and the water flows first through the head, then to the exhaust pipe, and then into the cylinders through the exhaust manifold. Note that the exhaust pipe is cooled by two different circuits-it is double walled only in the section that is supplied by the water that comes from the head. You'll also see a tee on the supply line that feeds water to the regulator valve that's mounted on the water box. This valve supplies cooling water to the box and the end of the exhaust pipe. The water that flows to the pipe also "tunes" the torque curve of the engine by altering the exhaust gas temperature. The flow rate of this water is controlled by the valve based on the pressure in the exhaust system, i.e. engine speed.

    Diagnosing an overheating engine is not easy because there's no way of measuring flow rates so you have to do what you've been doing and inspect all supply hoses and fittings. In your case I suspect there is some blockage that's preventing water from getting into the main supply line. You can check this with the boat in the water by removing the line either from the head or the regulator valve and seeing if there is a strong flow of water. If the plumbing after the muffler is melting, you're not getting enough water into the system. I hope this helps.

  3. #3
    So finally got back to looking at this. I started the engine, then backfed the water outlet with a garden hose. With it running I started removing hoses to see where I had flow and where I did not have flow. I seemed to have really good flow everywhere, huge stream coming out of the pisser, however I have a question about the water regulator valve. When I remove the larger line feeding that valve had tons of pressure coming out of it, when I remove the small line there was really just a trickle of water coming out of the valve itself. I put my finger over the valve outlet and really not much pressure. I realize its a regulator meant to regulate but wondering how to measure or know if its functioning properly. Any thoughts if I should see a better stream coming out of the valve? Also from what I have read when you backfeed these you can almost never overheat them, any truth to that? The only other thing I can think to look at is the wear ring to make sure the system is getting enough water into the system since I can not find any obvious blockage. Appreciate any tips!

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