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What(39)s the max RPM I should cruise Mercruiser 5.0LX

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    What(39)s the max RPM I should cruise Mercruiser 5.0LX

    I have a 2001 2455 Bayliner Ciera with a Mercruiser 5.0LX. The RPM gauge goes up to 6000 with no red line. When I push the throttle all the way up the RPM is at 6000 (5500 with a full tank of gas), and I'm wondering is it ok if I run it wide open all the time? I understand about how much more gas you use at high RPM for very little increase in speed, but what I care about is whether this engine is good to run at 6000 RPM all day long without any worries. It has always made me nervous running an engine at full throttle for extended periods but perhaps that's what these are made for. I welcome all opinion and your experiences but I'm most interested in what the manufacturer recommends which I can't seem to find online.

    Frank
    Last edited by Jim_Gandee; 01-29-2018, 05:20 PM.
    Franco

    #2
    Don't run it there! WOT is used for testing purposes only.
    Dave
    Edmonds, WA
    "THE FIX"
    '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
    (.030 over-Vortec top end-part closed cooled)
    The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
    Misc. projects thread
    https://www.baylinerownersclub.org/f...56-gctid789773

    Comment


      #3
      "builderdude" post=813987 wrote:
      Don't run it there! WOT is used for testing purposes only.
      AGREED.

      While not the same engine size or boat, I try and limit the RPM to about 75-80% of WOT. In my case when tested I reach 4,600 rpm on my carb'd 5.7's which equates to 3,600-3,700. This proves to be the sweet spot in my application for ride, performance and efficiency.

      Hope that helps.
      Sea Venture
      2000 3055, 5.7/B2, 18x23" props
      Cruising the PNW and beyond.
      DIYC, Riverhouse Marina
      MMSI 316029971

      Kirk
      Drinks well with others.

      Comment


        #4
        I think most guys tend to run the rpm at the slowest speed at which the boat will plane or a touch above. The fellas that have fuel flow equipment will likely run the rpm at where they achieve the best fuel economy. My 2556 will plane around 2900 rpm (pending conditions) but I'm usually running around 3200-3400 rpm.
        Dave
        Edmonds, WA
        "THE FIX"
        '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
        (.030 over-Vortec top end-part closed cooled)
        The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
        Misc. projects thread
        https://www.baylinerownersclub.org/f...56-gctid789773

        Comment


          #5
          If you can run that engine up to 6000 RPM you are way under propped!!!

          You need a prop that has a higher pitch! As in going from a 15 inch pitch to a 17 inch pitch!

          Good luck and enjoy your boat but DO NOT run it at 6000 RPM! Run it at a much lower RPM! But you should change that prop!

          Don
          1995 Maxum 2400 SCR LUNA DE MIEL
          1988 Bayliner 2455 (sold)
          1976 Tahiti 16.5 I/O (sold)
          10 ft livingston (lost in fire )
          1987 18ft. Seaswirl cuddy (lost in fire)
          "Is it better to be on a boat thinking about God, or be in church thinking about boating?"

          Comment


            #6
            mine also
            ..........
            1988 flybridge trophy bayliner 2556 ,mercury 5.7 lit. OMC cobra out drive 76 hrs. on new package,
            located in ketchikan ak,name DOMINION

            Comment


              #7
              I have contacted bayliner on this issue they have told me that 4600 rpm is max anymore you have the wrong prop.I run mine at 3200-3400 rpm using a 15.5 x 13 prop. that gives me 4100 rpm

              5.7 liter mercury carbed. engine cobra drive
              1988 flybridge trophy bayliner 2556 ,mercury 5.7 lit. OMC cobra out drive 76 hrs. on new package,
              located in ketchikan ak,name DOMINION

              Comment


                #8
                After 10 years with mine, the "comfortable" cruise RPM is 3600 to 3800 depending on the amount of slime on the underside and the amount of wave action trying to reduce your plane. I use my 8120 computer to monitor GPS speed and fuel flow to get a really good understanding where the engine is at its most economic at cruise. I run a 4 blade aluminium prop which was a revelation when I installed it.
                Terry (Retired Diving Instructor and Part Time IT Consultant)
                1998 Bayliner 2452. 5.7l V8 - Edelbrock 1409 4bbl - Alpha1Gen2 - Solent UK.
                MMSI 235061726

                Comment


                  #9
                  You are certainly over-revving your engine past 4800RPM, you should get a prop with at least 2" more aggressive pitch to get that under control and get better top end efficiency. For me best cruising RPM is between 3800 and 4000, I have 2004 Mercruiser 5.0 TKS (its a 305 cid double barrel carb with automatic enrichment for turn key start). I currently run 3 blade 16x16 aluminum prop and when lightly loaded I reach max RPM just barely where limiter kicks in near 4800 RPM. When heavy, I can only get about 4600 RPM, this means my prop is ideal for the weight of my boat.

                  On second thought, before you spend any money on props. Get a calibrated shop tachometer and actually measure your WOT RPM. I just can't believe 305 mercruiser would spin that fast without puking valves out in a hot mess. The in dash gauges can be inaccurate or faulty.

                  Comment


                    #10
                    Great answer, how can I find the specs of my prop? Are they on it? And is there a website I can go to try and choose the right prop?
                    Franco

                    Comment


                      #11
                      I'm curious myself now. I have a shop tach but the leads are short, I'll have to figure something out to read the rpm while cruising.
                      Franco

                      Comment


                        #12
                        There's an RPM limiter on Mercruisers?
                        Franco

                        Comment


                          #13
                          Yes, but only on those newer MPIs & TB5
                          Joon, Kathy, Jaden & Tristan
                          Uniflite 42 AC, DD 671N
                          93 3058 sold
                          92 2855 (day boat)
                          91 Fourwinns 205 (lake boat)
                          Longbranch WA
                          Life is Good

                          Comment


                            #14
                            My 5.0 2bbl is rpm limited to 4800

                            Comment


                              #15
                              "Jakeallred" post=815851 wrote:
                              My 5.0 2bbl is rpm limited to 4800
                              If you have a TB V ignition system, yes the Rev-Limiter is set 50 RPM above the maximum engine RPM.
                              Joon, Kathy, Jaden & Tristan
                              Uniflite 42 AC, DD 671N
                              93 3058 sold
                              92 2855 (day boat)
                              91 Fourwinns 205 (lake boat)
                              Longbranch WA
                              Life is Good

                              Comment

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