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Overheating on water pump, not on hose

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  • Overheating on water pump, not on hose

    I have a 175VMax that has been overheating at idle, but not at running speed. The water pump impeller looks fine. I pulled both thermostats and tested them, with both being fully open at about 135 F. When running the motor at idle in a drum of water the temperature will slowly rise until the alarm goes off at a piston head temperature of about 175 F. However, if I then hook up the fresh water hose connection and turn the motor back on, the temperature will slowly drop down to an idle running temperature of around 140 F on the starboard side, and 130 F on the port side. The starboard side consistently runs about 10 degrees higher than the port side, and seems to have a good bit more salt/corrosion build up than the port side when looking under the thermostat cover. That's relative though, because overall its pretty clean since I have never run it in salt water without flushing it. Any ideas?

  • #2
    Check the pressure control valve to see if stuck open.
    Regards
    Boats.net
    Yamaha Outboard Parts

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    • #3
      Your diagnosis was dead on. I had already put the parts on order by the time you replied, but it was good to have confirmation that I was on the right path. I bought the valve, grommet, and spring from boats.net for 12 bucks and change. There was no way to verify it was stuck open when I opened it as when you pull the cover off the spring pushes everything around. Accidentally pushed the old grommet inside trying to unseat it, taking several minutes to fish it out with a wire. I noticed that the new valve has a different design which looks like it is better designed to prevent hang ups. Recommend running a wire with a bent end through the grommet for insurance when removing the old or installing the new to prevent it from falling inside. Just ran the motor which now has a steady state head temperature of 125 degrees!!

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