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  1. #1

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    '98 GTX-RFI - Why did the exhaust pipe overheat?

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    The end of the exhaust pipe on my GTX-RFI got extremely hot (as evidenced by the discoloration) and the two rubber coupling hoses burned through. The engine was running fine and water was coming out of the bypass line. The engine was not abnormally hot. If I'm understanding the theory of operation correctly, cooling water enters the cylinder head first and then flows into the pipe to preheat the water before it enters the cylinders through the exhaust manifold. If this is the case, how can only a portion of the pipe be getting cooled? The boat was operating in clean, deep water and I inspected all of the water supply lines and the water control regulator for any restrictions.


  2. #2
    Myself's Avatar
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    Did you take the water valve apart? If the diaphragm gets a hole it won't allow any water to come up the hose and into the headpipe. The exhaust pressure builds on the backside of the diaphragm pushing up on the valve and letting water pass. If there is a rip or hole then it can't hold pressure and doesn't move. Then you don't get any cooling water inside the convergence cone and it gets really hot.

  3. #3

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    Yes, I did take the valve on the water box apart and everything looks fine but I may end up just replacing it since this is the only theory I have right now. I don't think the water that's supplied by this valve is meant to be a significant source of cooling water. It is used to change the torque curve of the engine by altering the behavior of the gases in the expansion chamber of the exhaust. In fact, it [U]reduces water flow as the engine speed increases.

  4. #4
    If i knew,...I wouldn't ask sea-one's Avatar
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    Sand or debris in the cooling when beached and clogged the small water line IMO- The small line had to melt off, replace the line replace the pipe and backflush the motor cooling and see from their. That looks minor, i've been them WAY worse and turn out ok....

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