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  1. #1
    Join Date
    Apr 2018
    Location
    Tottenham, Ontario, & boating
    Posts
    78

    Default Mercruiser 120 blowing exhast out the cooling lines

    Hello

    I have a buddy that bought my boat with a 2.5 mercruiser 1987 and now when he tries to start it, he says it just backfires out the carb and there is exhaust coming out the cooling lines. When I winterized the engine I took out the drain in the bottom of the block, and the drain in the bottom of the manifold with the nose of the boat slightly raised. I then disconnected the hose at the top of the thermostat and put a little antifreeze to flush out the water, just in case. What is going on with this troublesome engine again?

  2. #2
    Join Date
    May 2010
    Location
    DC Burbs/Maryland Eastern Shore
    Posts
    1,580

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    Head gasket fail will certainly behave this way
    Practicing the ancient art of ren-ching

  3. #3
    Join Date
    Apr 2018
    Location
    Tottenham, Ontario, & boating
    Posts
    78

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    would the backfiring blow a head gasket? what else could blow it?

  4. #4
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,101

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    That unique motor has its intake and exhaust manifold combined in one unit. It's possible a crack or rotted hole in the exhaust could send exhaust out the carb.

    Jeff

  5. #5
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
    Posts
    5,811

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    he says it just backfires out the carb and there is exhaust coming out the cooling lines.
    Ayuh,...... Back-fires through the carb is a symptom of a lean condition,......

    Aren't the coolin' lines full of Water,..??..??
    Any Grease is Better,... Than No grease at All....

  6. #6
    Join Date
    Apr 2018
    Location
    Tottenham, Ontario, & boating
    Posts
    78

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    ROFLMAO LOL LOL LOL.just realized what is going on. its not a head gasket or anything. this was buddy's first boat so he must have ran it on the trailer to see if the motor was working, and he ran it without ears, so now the pump is shot DUH... now when he put it in the water he tried to find out if there was any water coming out the cooling lines. Ya, you got it, lol, there is no water in the cooling lines, and the exhaust pressure just goes right back through the riser and out the cooling lines. Heh heh that was funny, lolz, though I freaked at first though. thanks for the help. lesson learned for him - try just not running it without ears, and then you wont have to buy an unneeded head gasket.

  7. #7
    Join Date
    Apr 2018
    Location
    Tottenham, Ontario, & boating
    Posts
    78

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    lean condition because the boat sat for a while and the carb must have dried out, and needed some cranking to get er going.

  8. #8
    Join Date
    May 2019
    Location
    where ever I am needed
    Posts
    23

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    Quote Originally Posted by vroomZOOM View Post
    lean condition because the boat sat for a while and the carb must have dried out, and needed some "crack" to get er going.
    ujgvuogvcuogvjrl.iablcfwef
    2004 29 fountain Fever. Twin 525 hp Mercruisers.

  9. #9
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,101

    Default Re: Mercruiser 120 blowing exhast out the cooling lines

    t;ot':L;y'u;]'iu;


    Me too!

    Jeff

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