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Weird 2019 Prostar 5.7 Overheating issue

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  • Weird 2019 Prostar 5.7 Overheating issue

    I have a 2019 Prostar with Ilmor 5.7. 350 hours, never any issues.

    The boat is used every week end and for the first time I got a stage1 205 temp warning.

    It’s not a sudden temp climb like there is no water flow. The boat runs at 170 for 4 passes at 34 and starts to slowly climb a little bit more each pass after this.
    Idling or running at 25mph seems to get the temp down a bit.

    Impeller was replaced a few months ago
    Strained housing and hoses were checked
    Thermostat seems to be working (opens and closes in hot cold water test)

    The gasket that sits below the thermostat was chewed though.

    At 205 the engine did not smell warm.

    Other that this the engine starts and runs great until alarm where it t would go into limp mode.

    Any ideas? I am planing to replace thermostat but was thinking it could be a bad temp sensor.

  • #2
    Is the gasket in the strainer? There's a small black o-ring that can easily fall out. Also remove the strainer and put it back on.

    If it gets warm at idle its getting air, bumping the throttle will cool it right down.
    If it gets warm over 2k RPM something is blocked or impeller.


    • #3
      @jgraham37128 Strainer gasket is fine. We checked it and removed it…

      Idle temp seems fine and Reving the engine does not clear it.

      The flow seems okay so maybe impeller. I would think if it was impeller it would get hot at idle


      • #4
        Then its not air driven. Blockage of some sort would be my guess.


        • #5
          my bet is the impeller is slipping on itself.. so when you go fast the fingers don't go around fast enough.. and when you idle you it is able to move enough water...

          replace the impeller...and test don't cheap out on the impeller either.


          • #6
            Starting simple. Are you sure the key for the impeller is in place?


            • #7
              Temp senders are relatively cheap, might be worth ordering one and replacing, and seeing if the problem goes away. I can try to get a resistance reading of mine so you can compare. But, if it's repeatable, maybe the sender is fine.

              After you get the temp down via idle or slow use, does it climb back up, every time?

              On the inlet of the CIRCULATING pump there is a restrictor plate in the 1.5" hose, with a small 3/8 or 1/2" hole in it. I've been told to remove it by two MC techs. Ilmor says that 1/2" hole is all the water the engine needs, but I've got 100 hrs on my engine with it removed with no ill effect.
              Last edited by mwagner01; 08-03-2021, 01:41 PM.


              • #8
                @curver900 That sounds probable. Impeller was replaced in October but you never know.

                @MIskiboat The boat ran a 100 hours so I am sure it is in


                • #9
                  SOLVED, Checked impeller and it was missing 3 blades, one stuck where the hose from the water pump to the block connects.

                  New impeller installed and all running fine. Impeller was 80 hours replaced last October.