1958 Sportwin Lower Unit Oil Question

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  • May 30, 2017 at 4:20 am #7169
    fishbrick
    Participant

      Hi everyone. It’s time for me to replace the oil in the lower unit on my 58 Sportwin.
      So, after looking in to what oil I should use, I’ve found a lot of conflicting information. For one the owner’s manual states “Use a reputable grade of SAE 90 automotive hypoid gear lubricant. If hypoid is not available, -in an emergency use SAE 30 engine oil, until recommended lubricant can be obtained.” But with contemporary sources on early 60s to 70s OMC’s, I find that modern marine oils should be used. The part that I’m concerned about is that many of the modern hypoid oils are corrosive to brass and copper. So, in your opinion which is better? Should I go with the manufacture’s recommendation, or with a modern marine oil?

      Btw, I also have on hand GL-4, SAE 140 Automotive hypoid oil; would this be a suitable substitute for 90 weight?

      May 30, 2017 at 4:59 am #58615
      david-bartlett
      Participant

        Just get some GL4 or 5 80/90. I personally use the Wal-Mart Supertech brand in all my motors that use oil in the lower end.

        May 30, 2017 at 3:33 pm #58630
        fleetwin
        Participant

          US Member

          Well, the 1958 Sportwin has the small gearcase, which was prone to water leaks, then terminal wear.
          So, if it were me, I would use the best oil available to avoid damage. The latest OMC/BRP/Merc/Yamaha gearcase lubes have the ability to absorb some water without losing too much lubricity….Cheap insurance.

          May 31, 2017 at 1:56 am #58666
          fisherman6
          Participant

            US Member

            I certainly won’t argue with Fleetwin here. It’s probably wise to use the best marine gearcase oil you can buy in the 4-bolt OMC gearcase on a 10 hp. I personally just use bulk GL-5 90W gear oil in mine. I do look to find something that says it is safe for use with yellow metals. I’m aware of the weakness of the 4-bolt 10 horse OMCs and I check them for water often and keep good seals in them. My motors don’t get left in the water either. I tilt them up when I dock or moor the boat. If you only change the gear oil once a year and leave the motor down all the time, I recommend something that has the additives in it that help maintain lubricity with some water present.
            -Ben

            OldJohnnyRude on YouTube

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