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Thread: Looking for help with an old Merc 50

  1. #1
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    Default Looking for help with an old Merc 50

    My smokercraft has twin Merc 50's on it. Both run. However one motor gets hot at idle and will die. The other motor seems to run strong, pees correctly and can push the boat up the Chena with about 500lbs of people it.

    I am curious on how I might go about fixing the one that gets hot? I was told that in the water jacket there are rubber gromets that act like a sort of ladder for the water to crawl up and that perhaps those have corroded and failed. Is this possible?

    Thanks!

    PS I am in Fairbanks if anyone is interesed in taking a peek

  2. #2
    Member alaskanmoosehunter's Avatar
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    Have you replaced the water pump? If you sucked mud or gunk at some point in time it's possible that it could plug up the pee hole. Take a peice of wire and make sure there is no obstructions through the pee hole.

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    I have not replaced the water pump, but I made sure the line for the pee hole was clear.

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    Member alaskanmoosehunter's Avatar
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    Quote Originally Posted by FairbanksBowHunter View Post
    I have not replaced the water pump, but I made sure the line for the pee hole was clear.
    It is very possible that the rubber impellers on your water pump are worn out. I don't know if you are the only owner of the motor. But I have seen people start their motors without water for 30 sec. or so. (Bad, Bad, Bad) It will ruin the water pump impeller just that fast or worse.
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    I am not the only owner. I have changed the impellers on both motors and NEVER ran them without them being in the water.

    Sure hope I can figure it out as I woudl really like to use it for moose season.

    BTW- the motors are like 70 models One is red the other is blue. Pull cord ignition

  6. #6

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    Since it runs atm and assuming you have muffs or a drum or such to provide cooling water for it on land, I would fire it up and check the thermostat operation.

    Those grommets or orings you speak of, by your description, sound like they are after the water pump, if that is the case they would allow water pressure fall but not likely all of the water to escape before reaching the pee hole. If they are below the water pump then the pump would have great difficulty picking up the water in order to pump it.

    The t-stat should be under a cover or small manifold and somewhat easy to spot, look for a round or oval "bump" on the side of he engine block. After starting the motor with the water supply on, feel for a cold area and a hot area on either side (if possible), or just install a new one. If there is a place other than through the hub for the cooling (or heated) water to exhaust (like the pee hole), feel it for temp. If it seems quite warm or hot I would get after the T-stat.

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    I've run lots of those 50's. If you know the water pump is good, then I would go down and get a gasket for the water jacket and remove it,( simple and cheap ) and see if the "ladder" as it is called is clogged with silt. This has happened to me a couple of times.

    The question do both of the pissers spray out the same, or is one weeker than the other?

    Good luck.

  8. #8
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    I have an older (late 60s) 50hp merc and I would have to check the manual to be sure, but I don't think mine has a t-stat.

    jets or props? either way I'd pull the jet or lower unit and inspect the water pump, try some low pressure water (use a water ballon fill nozzle!) to back flush the cooling (hook it up at the pee-nozzle or a hose close to it that is easy to access), and make sure the tube is aligned properly when reassembling (anti-sieze on the top of the shaft while you have it out).

    I had a 65hp merc recently that the impeller looked fine on, but the vanes on the impeller were bent the wrong way - so it just wasn't pumping the way it should. A few times taking it apart, putting it back together nefore I saw the problem and finally got it working right.

    whatever you find be sure to post what happens (sometimes these 'help' posts don't feature an ending...the resolution can be of great help to others that might be searching the forums with similar problems)

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