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Oil leak...

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  • #16
    I would double check your valve cover gaskets. I have seen oil leaks there that migrate unnoticed down to the bell housing. I struggled with this for a bit a couple of years ago.
    '78 20ft Cuddy
    Mercruiser 350 FWC preVortec w/Carb

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    • #17

      Rear main leaks are uncommon on GM or Ford 1 piece seals but high crankcase pressure can push oil past the seal.

      Make sure the PCV is working properly and consider replacing the valve.

      Fluorescent oil additive can be a huge help identifying the source of the leak.
      Steve
      1998 260 Mackinaw Sea Maxx 5.7 HO TBI 12' Klamath w/ 20hp Tohatsu EFI

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      • #18
        Thanks for the input, guys...

        I did a quick look-over on the valve covers, that was my first though but I didn't see any wet areas...also checked the distributor area and it was dry there.
        The remote oil filter adapter and hoses looked ok, but will take a more in-depth look at that also.

        I will check out the PCV when I get back to the boat.
        According to the parts manual, it is a 1 piece seal...

        This PCM engine has the oil drain hose (the one you drop out through the garboard drain to let the oil out) in place of the oil pan plug, I don't think it is leaking since the dip stick level doesn't change after sitting for a week...I figure if oil pan rust through or drain leak, the dipstick level should change between trips...???

        I guess it's time to shove the Go-Pro camera under the engine and see what I can see!
        1986 26' HT w/5.7 PCM 330HP RWC

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        • #19
          Alternate, proven solution to save your season. I had a small oil pan leak mid-summer '05. To get the though the season I took a plastic dishpan and supported it with bungee cords so it would hug the oil pan and stay under the drip. May have had to cut the sides down a little to make it fit (Don't recall.) Worked great! Simple.

          Footnote: Gave this engine and reduction gear to Jerry (Quick Fix) in '06 (after replacing engine) to reclaim garage floor space. This is how I met Jerry.
          Last edited by crhodes; 08-26-2020, 09:59 AM.
          C Rhodes
          26' Mackinaw - 1990
          351 Indmar (1990-2006: Great Engine)
          351 PCM (2006 - Current)
          Southport, NC

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          • #20
            FWIW - I ran the 20’ Shamrock for 5-10 years with a rear main seal leak. The engine ran great and I hardly ever had to add any oil to the engine between oil changes, but the small amount of dripping kept the bilge oily. A small amount of oil makes a big mess and the floating oil accumulates gradually fouling up bilge pump float switches. Since the oil floats on top of the water in the bilge and the bilge pumps never pump out all of the water in the bilge, the oil does not cause any noticeable pollution problems unless the accumulation of oil becomes excessive.
            Kingfisher
            1990 22' PREDATOR INDMAR 5.7 310 HP and ZF 45 C
            Fishineer
            1976 20' OPEN FISHERMAN Ford 302 and B/W 1:1
            Wilmington, NC

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            • #21
              Originally posted by crhodes View Post
              Alternate, proven solution to save your season. I had a small oil pan leak mid-summer '05. To get the though the season I took a plastic dishpan and supported it with bungee cords so it would hug the oil pan and stay under the drip. May have had to cut the sides down a little to make it fit (Don't recall.) Worked great! Simple.

              Footnote: Gave this engine and reduction gear to Jerry (Quick Fix) in '06 (after replacing engine) to reclaim garage floor space. This is how I met Jerry.
              Little more detail: Suspended the oil pan using bungee cords with hooks placed in small holes cut into dishpan. The other end was tied to engine mounts (I think). This raised the pan where bilge water should not move it. Also, it doesn't take much oil to really mess up a bilge so you probably won't have to empty it often. (Didn't see a leak rate mentioned.)
              C Rhodes
              26' Mackinaw - 1990
              351 Indmar (1990-2006: Great Engine)
              351 PCM (2006 - Current)
              Southport, NC

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              • #22
                Not a big leak rate, just enough to make oil fish-eyes in the standing water in the bilge but not bad enough to see a drop on the dip stick yet.

                Been putting dish washer soap in the bilge before each trip to let the sloshing action break up the oil then pump it out at the end of the day.
                1986 26' HT w/5.7 PCM 330HP RWC

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                • #23
                  If you throw a "baby diaper" oil absorber in the bildge too, I would think you would be good for awhile?

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                  • radioman
                    radioman commented
                    Editing a comment
                    Good idea!
                    I'll grab a few from work.

                • #24
                  Not pushing the dishpan/bungee idea but it really does work well for this type of leak with no mess. Your leak rate sounds like mine and I too did the soap thing for awhile but still had the oil dripping when not in use so figured a better way. (I keep the boat in the water and didn't want to risk getting giggled for an oil sheen, plus wanted to keep the bilge and marsh clean.) Good luck making it to season's end.
                  C Rhodes
                  26' Mackinaw - 1990
                  351 Indmar (1990-2006: Great Engine)
                  351 PCM (2006 - Current)
                  Southport, NC

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