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Mercruiser 3.0 rpms suddenly higher than normal

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  • Mercruiser 3.0 rpms suddenly higher than normal

    Hi all,
    Have a question about sudden high rpms in a mercruiser 3.0. The engine is showing 4900 - 5000 rpms at 35mph?? This has just started happening and is certainly higher than it has run in the past. I know the prop hub is not slipping as prop and hub brand new...any ideas as to how to troubleshoot? Thinking I should get a digital tachometer to double check the tach is working correctly? Any other help appreciated.
    Thanks

  • #2
    Agree check with another tach and hope its just the boat tach

    If it isn't the boat tach then the next question would be, do you smell burnt rubber?
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 Seadoo GTX
    Merc Adults Only VP Adults Only
    G-Dad always said "First Liar doesn't stand a chance"

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    • #3
      Thx alldodge...
      no smell of burnt rubber.....what would that indicate if there was?
      Thx

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      • #4
        On board tachometers have a switch in the back to configure them for 4 cylinder, 6 cylinder or 8 cylinder motors. That switch can get corroded. If that is the problem, then if you can cycle the switch around a few times you may get it back to reading correctly.
        17 Foot '90 Bluewater
        Alpha 1 3.0 Merc - repowered in 2016
        now - 4.3L Vortec - Alpha 1 GenII
        Honda BF100L kicker
        Engine custom - Transom 0D65328 - Drive 0D648864
        If you ain't fishin, then yer working too much.

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        • #5
          Thx Rick....I take it you mean the back of the actual guage?

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          • #6
            Sign up today
            Originally posted by trooper1954 View Post
            Thx alldodge...
            no smell of burnt rubber.....what would that indicate if there was?
            Thx
            If you smell burnt rubber and the motor speeds up and boat slows down the that's the engine coupler

            And yes, look on the back of the gauge to see if the tach is not setting on the correct position
            94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
            95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
            07 Seadoo GTX
            Merc Adults Only VP Adults Only
            G-Dad always said "First Liar doesn't stand a chance"

            Comment

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