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Mercruiser 260/350 oil leak

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  • Mercruiser 260/350 oil leak

    Late last summer a leak began towards the lower rear of the engine. I wasnít able to diagnose the cause this fall, but am going down next weekend. Iím not confident enough to pull the engine and diagnose, but I was thinking about doing the following:
    hook up and air hose to the dipstick and put a psi or 2 into it. Go through and tighten up oil pan bolts and inspect the pan plug feeling and looking as best I can for leaks. If I canít find anything that way then off to Lingo it goes. Thoughts?

  • #2
    have to block any breathers in the valve covers..
    Proud parents of a US. Soldier. 15 years & still going!

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    • #3
      I had to put additive in oil and use a black light

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      • #4
        Engines are known for pinholes in oil pan
        I smell fish!!

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        • #5
          Yes, check the oil pan carefully with a mechanics mirror, or one of those bore scope lights you can get for your phone. A leaky pan is a very real possibility. Also check the area around the rear main seal. The pan gasket could be leaking but don't just start torquing the bolts or you may make it worse and even break a bolt. Also, make sure oil isn't running from a valve cover, down the back of the engine and dripping off the pan. Good luck.

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          • #6
            some of those pans are made of metal and get rust holes in them a friend of mine had to replace his because of rust holes in his. I hope it something simple for you

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            • #7
              Jim - thanks I would have forgotten about that. I could try the dye method, but I canít start the engine. Itís just a slight leak, but does leak some when the engine isnít running. I guess if I put the dye in and crank it over a few times, then let it sit for a few weeks and come down again maybe Iíll be able to see where any slow leaks are coming from.

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              • #8
                Many years ago I did this with a 302 Ford in a 24" boat. Came down and got the boat ready to fish the for Trout. Went home and waited for a friend to call when the Trout are out of the bay and on the pimple. The Trout moved, I came down, splashed the boat, fired her up and blew the engine.

                My $.02 pull it out and fix it.
                That's all she wrote.

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                • #9
                  Well it will get fixed either way. Iíll likely end up taking it in because I just donít want to deal with dropping the engine back in. Iíd just like to have a good idea of whatís wrong before I take it in. If my cousin (certified marine mechanic) can find time weíll do it ourself, but not likely.

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                  • #10
                    My leak was a timing cover don't waste time looking for a leak you can't run it that way.very easy to pull engine minus rusty bolts.pull outdrive front and rear mounts couple bolts to flange couple hoses and wires.mark everything with duct tape .a backhoe or wrecker could lifT it out.2 4x4 across gunnel use a coma long to lift it up to make sure it's free.

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                    • #11
                      My leak was a timing cover also.

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                      • #12
                        The leak is towards the rear. I put dye in it this afternoon. My fear is itís the rear main seal.

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                        • #13
                          Nick there's a guy on Craigslist that has reman long blocks.might be time to rebuild money you spend on good and not fix old.is that a 6 or 8 cly.

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                          • #14
                            Craigslist boat parts 260 $500
                            Last edited by stressfree; 02-18-2018, 07:00 AM.

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                            • #15
                              You should be pulling the outdrive every year anyway, you can't grease the U-joints or inspect the bellows if you don't. With the outdrive pulled it literally just takes a few minutes to pull the engine, unless you have frozen hardware. And fixing the leak will require pulling it. If it still runs ok & compression is good I don't think I would buy a new engine because of a rusted oil pan, but that's me. To lift the engine, a wrecker, front end loader, backhoe, forklift, etc, works great. Or a regular shop crane like you see in nearly every garage for pulling car engines does a fine job. Put the crane on the back of another trailer, boom extended, legs retracted. Chain the back of the crane to the trailer to compensate for the shortened legs. Back the crane up close to the transom, hoist the engine high enough to clear, move either the boat & trailer or the crane trailer with the engine hanging, lower the engine and you're done. Repair or replace the engine and reinstall it the same way. Be sure to check alignment with a dummy shaft before installing the outdrive.

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