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Thread: Tohatsu / mercury 3 cyl water on plugs.

  1. #1
    Team Member ice_spy's Avatar
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    Default Tohatsu / mercury 3 cyl water on plugs.

    I have a tohatsu md50, 2003 3 cyclinder. Motor was running fine for approx 3 hrs then blew a head gasket. Possible cause was a blocked thermostat with a bit of plastic lodged in there.
    Gutted thermostat, skimmed head approx 6thou and skimmed deck / black approx 10 thou. Only enough to flatten the surface areas.
    Motor has little to no corrosion. No pitted edges on flat surfaces.
    Replaced two head gaskets now, torqued properly to spec stamped on head. 18 ft pound.
    New bolts installed.

    Again tested today with new gasket and still plugs coming out milky. Dropped in the water for quick run and no power due to water in cyclinders. Definitely leaking, not just moisture in the block.

    The only thing I can think of now is that the gaskets used are non genuine and maybe not sealing as good as original gaskets?
    Base gasket has been replaced but power head pulled on off 3 times, gasket still looks ok nice and thick with no tears but maybe this is not sealing and somehow ingress water through the base plate gasket?
    I don't know what else to do, my boat is out of action until I can get this water leak fixed. The head looked good with no signs of cracks, although I have not pressure tested the head. Could the exhaust ports cooling plate be leaking somehow?
    I was under the impression that only a head gasket would allow water in the cyclinders not a base gasket or side cover exhaust plate gasket.

    Any help or suggestions would be most appreciated, I can not afford to keep buying head gaskets and now I don't even know for sure what it is. The only option I thought was to replace the head gasket with genuine and try again.
    The race never stops

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    look at the bace gasket, and exhaust cover gaskets. i'd pull exhaust covers have a look in there. right after i checked the fuel tank to see if any water in fuel.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

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    Team Member ice_spy's Avatar
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    No water in fuel, so it's possible if the side cover exhaust plate gasket has failed this could allow water in the cyclinders ? Also if the base gasket failed this could also allow water in the cyclinders? I will check the exhaust plate cover side plate gasket 1st and see what I find.
    Thanks Fred.
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    FFX-61
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    yes, ether of those could leak and wet it out, exhaust is easiest so go there first, should be a tell tale spot were it's leakin in.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

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    Team Member ice_spy's Avatar
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    I really appreciate your advice to help me. So far no one else can/ has. Even marine workshops.
    Could I do a compression test to attain if the head gasket has failed again or if not the water then must be coming in from somewhere else ? Like the exhaust post cover.
    The race never stops

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    yes, you could comp' test it. that will let you know the head gasket is sealed up, and the leak is one of the other two. then pull the exhaust covers see what you can see.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

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    Team Member ice_spy's Avatar
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    Ok so as I have another spare head gasket I pulled it to be sure of good seal. These are the pics. It seems there was very good seal and gasket glued / stuck to both surfaces. Comp test showed cyclinders to be at approx 103 psi average. I did hit a spike on first test showing 130 psi in one cyclinder but on 4 more tests could not get that figure again. I guess I have no other choice than to pull the side plate and inspect / replace gaskets. The lower cyclinder seems to be the wettest so that could indicate a leak from the side cover maybe ? Due to gravity ?



    In order block, head with gasket on, head with gasket removed surface gasket to head side up.
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    Team Member ice_spy's Avatar
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    Ok so I only snapped 7 out of 14 bolts... that's a good start. Lol. Applied heat and inox spray but they were definitely not coming out easy. Didn't want to apply too much heat to the plate. At least they are a stud to remove and didn't snap flush with the block.
    So as you said Fred, it appears the gasket was leaking. Looked like it failed around the top of the plate which would allow water to fall to the bottom cylinder? as it did seem bottom was wettest then middle then top the dryer.
    I will replace the head gasket I think i do not need genuine this gasket seemed to seal good, but i will purchase genuine for the side plate cover. Now to try and remove the broken bolts without me doing any more damage. Wish me luck.


    Thanks Fred, really didn't want to remove this side cover exhaust because I knew bolts would snap but what option did I have really. Had to be done.
    The race never stops

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    Team Member ice_spy's Avatar
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    So after some Google reads, is the best method to remove broken studs that are not flush with the surface to weld a nut on the end of the broken stud and shock them off slowly with some spray, any particular rust penetrate spray in a can recommended?
    The race never stops

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    Team Member zul8tr's Avatar
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    I would not weld a nut. Those studs look long enough to grip tight with lock pliers. I have had luck doing that + penetrating spray like PB Blaster or better yet Kroil spray (see below) + some heat on the aluminum casting not the stud. Apply the spray let sit awhile, some heat on casting then lock pliers rocking CCW and CW a bit (careful here patience) to break the bond and not the stud add more penetrating spray and work in intervals of heat and rocking with the pliers. Before you close it up I would clean that scale off the cooling area with some pool acid (muriatic). Dab with a brush and flush with water carefully keeping out of pistons and cylinders.

    If studs break off next step is drill and easy out tool or drill and retap, hard to get center here but doable.

    Kroil

    http://www.kanolabs.com/penLub.html#anchor173855
    " Three may keep a secret if two of them are dead" Ben Franklin
    " ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
    Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress

    Location: SW Orlando, Fl

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