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How Low an RPM is too low

FrankHD Member Posts: 16
I have a 2020 Sundeck 188 IO with a 200HP 4.5L Mercruiser with a 4-bladed prop.  It will go 40+ mph but I don't think I have ever seen the RPMs go as high as 3,000.  A search of the forums seems to indicate a lot of folks are seeing RPMs in the 3500 - 6000 range, which seems awfully high to me when I think about a car engine (which obviously has a transmission with gearing).  Is a low RPM worse on an engine than a high RPM?


  • cjjjdeck
    cjjjdeck Member, Moderator Posts: 1,872 ✭✭✭✭
    The RPM's range is determined by the engine manufacturer.  Marine engines are designed to withstand sustained higher RPM abuse (much like race car engines).  Engines used in automotive service are NOT marine engines.  It stands to reason that lower RPM's put less wear on an engine over time.

    Below are the specifications of your engine based on what you mentioned.  At Wide Open Throttle (WOT), your engine should be pushing somewhere within the 4,400 - 4,800 RPMs mentioned in the specs.

    2012 SD237 I/O Mercruiser 5.0L MPI ECT/ Bravo 3
    2012 Load Rite Elite Tandem axle trailer

  • FrankHD
    FrankHD Member Posts: 16
    Thanks again for the quick response.  Was out on the boat last weekend on relatively flat water and at 35 mph I was at 1900 rpm.