1957 Merc Mark 25 not warming up

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  • GUY SCHMIDT

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 25
    Topics: 16
    #283043

    Started above motor for first time after purchase. Ran in barrel for several minutes. Head getting warm to the touch but tell tale stream still cold. Is this normal .


    crosbyman

    Canada Member - 2 Years
    Replies: 3557
    Topics: 324
    #283048

    how warn     medium warm     burning warm ???

    did you replace the impeller  and gear oil  …first thing to do on a new ..motor

    tell tale may not always include cooling water  it may  be sent down the exhaust  housing nowhere to be seen ..and out the prop    the tell tale tells you the pump is pumping

    can you meaure the PH temperature with a IR gun

    Joining AOMCI has priviledges 🙂


    GUY SCHMIDT

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 25
    Topics: 16
    #283058

    I’d say low to medium warm. And I wasn’t the guy who rebuilt it. I was wondering if there could be blockage that diverts the water out the tell tail and doesn’t cook the engine?


    crosbyman

    Canada Member - 2 Years
    Replies: 3557
    Topics: 324
    #283059

    no thermostat expert but in general water always go right back out via the tell tale and the thermostat  only allows new  cooling water to be circulated around the cyl jackets by releasing the jacket  hot water  when the temp exceeds around 140 deg.

    in the attached diag. on a OMC  engine tell tale water would get warmer after a while.  since your’s does not I suspect Merc’s  dump  it down the internal exhaust  housing…to also  provide cooling

    if your engine ever gets burning hot then  there is a problem. A cheap IR gun will tell you  the temp on the PH  and a   hot spot  would indicate blockage needing attention

    If not a stuck impeller blade  it  could be just  accumulated sedidements which  you can flush out with commercial products.

    Joining AOMCI has priviledges 🙂


    frankr

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 6695
    Topics: 51
    #283062

    No thermostat on a mark 25]


    crosbyman

    Canada Member - 2 Years
    Replies: 3557
    Topics: 324
    #283063

    there you go then … even simpler   extra cooling needed or not ! May explain why tell tale is cooler than expected  !

    thanks for clarifying.

    Joining AOMCI has priviledges 🙂


    billw

    US Member - 2 Years
    Replies: 2071
    Topics: 66
    #283125

    You should be able to hold your thumb near the top of the block while it’s running. If you can’t, it’s too hot. (Don’t forget the moving flywheel.)

    Long live American manufacturing!

    1 user thanked author for this post.

    GUY SCHMIDT

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 25
    Topics: 16
    #283136

    Thanks again for your time and help


    jeff-register

    US Member - 2 Years
    Replies: 1531
    Topics: 54
    #283165

    Guy,

    I had cooling problems with a KF5 very similar to the mk 25. I pulled the water jacket cover off the cylinder, has no head., very carefully, the bolts break easy, used a  torque wrench, using max touque in rweverse as to not use excess torque rating & a little heat on  the cylinder threads& panther piss to loosen to get them out.

    then used anything that woulld fit in the cylinder cooling passage to scrape the surfaces clean then hose out & removed a large amount of junk from the area. Next I reversed thru the water release hole where the discharge  is to clear that passage, then put back the water jacket cylinder cover. NEVER scrape the cover or cylinder top as it will leak if you do. Install new fasting  bolts or studs so next time you  remove only nuts to service, MUCH easier, use stainless studs & steam pipe thread lubercant, comes in a small tube like toothpaste to insure removable, looks silver paste. The  water exits from the wateer pump up a copper pipe up the   leg to the water passege into the exhaust cooling side cover & fills that passge then the cylinder cooling area then exits thru the exit passage & a weep hole inside  the leg to cool the exhaust. Very important to keep the bottm crankshaft seal good as the water exit is next to exhaust outlet. The seal is placed downward so inportant because any unburned fuel inside the crankcase is pushed out into the leg to keep from fuel collecting in the crankcase. I also have seen broken  blades  from  the waterpump stuck  in the watertube in the leg so it would impede water flow, Also on some watertubes the bottom cut were cut flat & if they vibreae down very little & impede water flow. Mercuy found this mistake early & started cutting the water tube at a 45 degree angle.  It’s worth it to pull the powerhead, replace the base gasket & bottom crankshaft. You will know if the top crankshaft is bad as fuel vaper will soak the mag & no spark. If you do the top seal , (I would) Get a pitman arm remover & dremel it to fit the magnetic rotor to remove the roter to remove the magneto plate to get at the top seal, two screws going sideways for plate tension. Clean & relube friction surfaces, use an inert light grease. Crankshaft seals are like shoes, never install one, do the pair! Your idiling will  improveSO much & save your rod bearings from sucking discharge water into the crankcase!!! P.S. The drawing shown is for OMC (Evinrude & Johnson motors). Mercury has no head or gasket, only a cooling waterjacket cover. The pistons install from the crankcase up because the cylinders0n were machined as one piece. I guess because of high compression Carl thought they would blow head gaskets, so he made them one piece & resolved the possable problem, in my opinion. Who’s Carl??? anyway?

     

     

    Good luck

     


    GUY SCHMIDT

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 25
    Topics: 16
    #283356

    Guy,

    I had cooling problems with a KF5 very similar to the mk 25. I pulled the water jacket cover off the cylinder, has no head., very carefully, the bolts break easy, used a  torque wrench, using max touque in rweverse as to not use excess torque rating & a little heat on  the cylinder threads& panther piss to loosen to get them out.

    then used anything that woulld fit in the cylinder cooling passage to scrape the surfaces clean then hose out & removed a large amount of junk from the area. Next I reversed thru the water release hole where the discharge  is to clear that passage, then put back the water jacket cylinder cover. NEVER scrape the cover or cylinder top as it will leak if you do. Install new fasting  bolts or studs so next time you  remove only nuts to service, MUCH easier, use stainless studs & steam pipe thread lubercant, comes in a small tube like toothpaste to insure removable, looks silver paste. The  water exits from the wateer pump up a copper pipe up the   leg to the water passege into the exhaust cooling side cover & fills that passge then the cylinder cooling area then exits thru the exit passage & a weep hole inside  the leg to cool the exhaust. Very important to keep the bottm crankshaft seal good as the water exit is next to exhaust outlet. The seal is placed downward so inportant because any unburned fuel inside the crankcase is pushed out into the leg to keep from fuel collecting in the crankcase. I also have seen broken  blades  from  the waterpump stuck  in the watertube in the leg so it would impede water flow, Also on some watertubes the bottom cut were cut flat & if they vibreae down very little & impede water flow. Mercuy found this mistake early & started cutting the water tube at a 45 degree angle.  It’s worth it to pull the powerhead, replace the base gasket & bottom crankshaft. You will know if the top crankshaft is bad as fuel vaper will soak the mag & no spark. If you do the top seal , (I would) Get a pitman arm remover & dremel it to fit the magnetic rotor to remove the roter to remove the magneto plate to get at the top seal, two screws going sideways for plate tension. Clean & relube friction surfaces, use an inert light grease. Crankshaft seals are like shoes, never install one, do the pair! Your idiling will  improveSO much & save your rod bearings from sucking discharge water into the crankcase!!! P.S. The drawing shown is for OMC (Evinrude & Johnson motors). Mercury has no head or gasket, only a cooling waterjacket cover. The pistons install from the crankcase up because the cylinders0n were machined as one piece. I guess because of high compression Carl thought they would blow head gaskets, so he made them one piece & resolved the possable problem, in my opinion. Who’s Carl??? anyway?

     

     

    Good luck

     

    Thanks, I didn’t see your message earlier and wasn’t on line for a bit. Great info.

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