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Air leak on raw water suction side

Discussion in 'Technical Discussion' started by Pascal, Dec 6, 2012.

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  1. Pascal, Dec 6, 2012
    #1
    Pascal

    Pascal Senior Member

    Joined:
    Feb 29, 2008
    Messages:
    8,546
    Location:
    Miami, FL
    This was a new one to me... 1400hp Cat 3412Es

    For the past few months, I ve noticed the stbd tranny running a little warmer than the port at low speed only. On plane, temp would come down and both would be close

    I checked the obvious ( strainer, impeller, debris in the cooler inlets...) and couldn't find anything. Engine coolant temp was fine. It was one those things that wasn't broken enough to start doing expensive things like pulling coolers etc

    Then one day after a start i realized the raw water pump cover was heating up and not priming. That was quickly addressed by re priming thru a plug just down stream but clearly there was a problem

    Next day i did some testing and with nothing else running in the ER i heard a gurgling sound when shutting down the engine, coming from the raw water pump area.

    Took me a couple of hour to find the cause... Turned out to be a very small hole in the fuel cooler which on these engines is on the intake side of the raw water pump. It was almost impossible to see being in a hard to inspect part of the flange and at first it just looked like a paint chip.

    Being on the intake / suction side, it wasn't leaking but would cause water to drain back out the thruhull. It wasn't big enough to cause overheating, just a slightly warmer tranny at low speed only

    A bit of 4200 on the hole temporarily fixed till a new cooler could be ordered. Sure enough, both trannies are now running at the same temp.

    So when all else fails, listen carefully and turn other things off if you have too. Air con compressors or a generator would have covered that sucking sound...

    And if you have start/off switches in the ER, it s a good idea to use them, at least for the first start and the last shut down of the day . Starting from the ER also recently alerted me to a starter that was about to go instead of being caught later with a dead engine. I ve also developed a habit of touching the raw water pump cover after the first start of the day

    Attached Files:

  2. Capt J, Dec 6, 2012
    #2
    Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
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    Location:
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    Judging by the reddish color of the bronze in the area's above where the hose is on the closest part to it to the picture, you might have a little electrolysis issue going on as well. I would check that out as well and make sure all of your engine zincs are in good shape.

    I had a similar issue on the first boat I was in charge of caring for, a long long time ago. The only time the engine would run hot is under full throttle, then one time, it overheated idling at the dock warming up. We did impellors, heat exchangers, etc. It ended up being an elbow on the intake side of the pump that was slightly warped.
  3. Swamp fox, Dec 6, 2012
    #3
    Swamp fox

    Swamp fox Member

    Joined:
    May 19, 2010
    Messages:
    85
    Location:
    NC
    I have the same motors and fuel coolers on the Marlow I'm on. Every other year, or more often if need be, I'll take off the intake hose from the seacock to expose the cooling tubes of the fuel cooler. I'll check the heat exchanger tubes for blockage. Its amazing the crap that finds its way in there. Motors aren't getting hot, but still. Bits of calcium, grass, candy coral that the diver can't reach, etc. It all winds up in there and needs to be checked. Don't forget to change the zinc thats on the cooler as well. Small pencil that gets changed often because it is so tiny. Alot of water passes over it.