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Mercrusiser synthetic vs non-synthetic?

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  • Mercrusiser synthetic vs non-synthetic?

    Soon, I will have to change oil in my MC 383s. I have never been a fan of synthetic oils in boats since I normally change oil yearly and don't want the extra expense associated with more expensive synthetic oils. But, then a friend told me that once a motor has used synthetic oil, you can't go back to traditional oils. I have never heard of this before? I plan on (hopefully) using Valvoline 20-40!

  • #2
    Sorry your friend is wrong. I haven't heard that one for a long time.
    You can switch back and forth.
    1980 Sylvan Aluminum 18' Sportster I/O - Mercruiser 140, Honda 7.5 Kicker, Bennett M120 Tabs
    1974 Glastron V-179, Mercruiser 140
    1984 16.5ft. Alumarine Sealark side console with 82 Merc 50
    Manitoba, Canada

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    • #3
      Why bother with anything but the cheapest possible oil? Engine isn't going to last long enough for low quality oil to cause any problems.
      xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
      The world takes on a whole new perspective when viewed from 100’ below.
      1972 Bertram ‘Bahia Mar’ 20
      2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
      (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


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      • #4
        Thanks to all! I dive a 1995 Chevy truck that has run perfect on regular 10w40 and for decades. My wife's vehicles all use synthetic per manufactures' recommendations. I didn't want to ruin good marine V8s due to ignorance.

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        • #5
          Each of the last five vehicles purchased in our family require syn engine oil. This says something about the quality of syn oils. Merc's 20-40 syn is a little over $8/quart. Cheap insurance for a superior product.
          '96 Larson 174 SEI BR. 4.3LX 4 bbl Weber s/n 0F786604. Alpha One Gen II s/n 0F709315

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          • #6
            People will debate this question all day.. Some guys are pro synthetic and run it in every engine they own.. others prefer sticking to the original manufacturers recommendations. I don't know there is a right or wrong answer, just more of a personal preference. I think synthetic oils are great. But I don't think they perform miracles. If the engine was built in a time before synthetics.. I run standard oil in it. Nothing wrong with regular oil if changed regularly.
            As far as switching between the two oils.. I always like to flush the old with the new.. effectively doubling the cost for the first oil change. May not be necessary but just one of my quarks I guess.

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            • #7
              As far as I know the Merc/Quicksilver oil is available in regular and semi syn. I know they used to sell a full syn but that has been discontinued. I have used the regular 25/40 in my old engine and it holds good oil pressure after running on plane and tested out well when a did a Blackstone oil analysis back in 2014. I think this oil is better than car based oils esp if you don’t have engine oil coolers as most Merc and Volvo small blocks do not.
              i know Volvo recommended a full syn 10w/40, which you could use if you really want a syn. Personally I’d use the Merc regular 25/40. Easy to find everywhere and holds up well.
              1988 Four Winns 200 Horizon
              4.3 OMC Cobra

              98 Jeep Grand Cherokee 4.0 Selectrac
              07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

              "While air doesn't freeze....rust never sleeps"

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              • #8
                Thanks again to all!!!!! These engines are 4 bolt main with manual fuel pumps so I suspect less tight than new motor designs. But the new stuff definitely has tighter tolerances. My old 95 Chevy is like the Energizer bunny but I don't run it much past 3 grand. My MCs will probable never turn much past 3 grand either. They are closed cooled but the damn Gulf of Mexico in NW Florida is already near 85 degrees at the surface. I suspect I will go with Valvoline regular mult-weight oils. THX AGAIN!

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                • #9
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                  Hi. Not sure there is such a thing. There is a quicksilver synthetic blend, which is a semi as far as I know. I use this only because it’s better than the standard quicksilver 2540 junk. It isn’t much better to be honest but does hold its form a little better than the normal stuff, come the end of the season. If it wasn’t for me wanting to stay OEM...there are plenty much better oils out there for sure.

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