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Oil to fuel ratio

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  • Oil to fuel ratio

    I know I’d read about this subject before, but can’t remember where. At any rate, with today’s synthetics how much less oil can you get away with on an older motor? 16:1 is a ridiculous amount of oil in my opinion if used with today’s better oils. I’m just not quite sure I want to be the one to figure out how little can be used. I cautiously use a ratio of about 25-30:1. Curious what y’all think…?

  • #2
    I'm a true believer of the Amsoil interceptor synthetic oil. I use that in everything from 1950s Merc 2 cylinders, dirt bikes, to my newer jetskis with power valves (they get very gummy with regular oil). That being said, everything gets slightly under 40:1 since I'm a bit generous with the pour. I've never had problems since going with the synthetic at that ratio, and everything runs a lot cleaner. Both the outboards and jet skis say they want 30:1 or below. This is just my level of comfortableness with this particular oil and running the motors slightly rich, but it seems to work.


    • #3
      More on oil ratios


      Important how you intend to use the engine, idle a lot, moderate revs, or high revs when off idle like racing. To quote retired racer winning engine builder Jerry Wienandt - Trident Merc Master "Oil is cheaper than parts"
      "Keep Move'n" life is catching up!
      No man's life, liberty or property are safe while the legislature is in session.


      • #4
        Dig it! I’ll jump on the link, do my homework, then form my wild ass guess hypothesis. “Oil is cheap”, cheap like gold is cheap these days! Moron this subject in a bit!


        • bill hoctor
          bill hoctor commented
          Editing a comment

      • #5
        Ok, I’ve learned the lesson and will not soon forget it! Basically the only real oil ratio changes is for trolling or idling excessive conditions and going to a lighter amount of oil to gas could help cut down on carbon build up and potentially fouled plugs. If the intention is WFO, then one best be using heavier oil ratios and spend some time getting the jetting correct. Thanks a bunch guys!


        • ZUL8TR
          ZUL8TR commented
          Editing a comment
          On my 1972 25ss I ran back in the 1970's race days and now still run 16:1 with 99% of time wide open at 7000+ (now using Pennzoil XLF, have tried other oils and settled on XLF, best results for me). No carbon in combustion chamber and zip on the piston crown and plugs run perfect color no carbon with OEM 61 fixed jet for sea level to 4000 ft. Idle and low revs not good for these race engines. As Trident states these old Mercs have full complement needle bearings at the crank and piston pin and they need lots of oil at 7000+. Also I have never had a problem running 87 octane fuel (E free these days) in these low compression engines. Never had octane knock issues and piston failure, or any other failures. Same complete engine from 1972 still in great shape, good maintenance is essential especially that unobtanium Quicki gear case ;-)

          More reading. Here is a 2 cycle oil ratio article by Gordan Jennings from years ago done for motor cycles I find applicable for race outboards on the oil theory he discusses.


          Happy trails