Water Ingestion Into I/o Merc Engine

Discussion in 'Powerboats' started by Boatwiser, Sep 22, 2015.

  1. Boatwiser
    Joined: Sep 2015
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    Boatwiser New Member

    WATER INGESTION INTO ENGINE
    I welcome your advice in helping me to decide whether to repower a 1997 bowrider, built by a renowned manufacturer. The main issue for me is whether it is worth putting a new motor in, given the possibility of water ingestion up through the exhaust system. Our boat is a 21 foot single I/O . It has a 5.7 liter, 250 horsepower Mercruiser engine, normal carburetion.
    We have experienced water ingestion into the motor in several different ways. See Mercruiser Service Bulletin 2001-11 for ways this can happen. What I am most concerned about at this point, however, is the possibility of water coming up through the exhaust system. That has happened to us a couple of times.
    While I understand that this water ingestion up through the exhaust happens infrequently, it still seems (from talking to others) that it happens far too often. Was there a design mistake or miscalculation when exhaust / motor systems were placed into some I/O bowriders in the late 1990s? Have manufacturers made any adjustments to prevent this from happening in subsequent years?
    Any advice or thoughts that you have about whether it's worth repairing this boat are most welcome. The cost to replace the engine would be about $6,300. The boat is in otherwise good shape for its age.
    Thank you.
    - Boatwiser
     
  2. gonzo
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    gonzo Senior Member

    That price seems really high. A long block should a lot less, maybe 1/3. Some manufactures installed engines with risers that were to low. The problem can be fixed with spacers.
     
  3. Ike
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    Ike Senior Member

    Water ingestion can occur due to risers that are too low, and due to a missing or inoperative shutter valve in the exhaust. These valves are supposed to prevent any water from coming up the exhaust, but they are frequently damaged by running the engine without water being injected into the exhaust (happened to mine.)

    Yes there have been instances of boat owners complaining about this in the late 90's I can remember getting several consumer complaints about it but I don't remember which boat manufacturer it was. At least one was due to low risers and the owner putting too much weight in the back of the boat. The other case was quite frankly a person who just liked to write letters of complaints. He did have a problem and higher risers fixed it. But he complained about everything on his boat. I still wonder why he even bought it. As far as I know none of these ever rose to the level of requiring a manufacturer to do a recall.
     
  4. tom kane
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    tom kane Senior Member

    Any boat motor with a wet exhaust system is subject to water ingestion.
    Any water or vapor in an exhaust can be drawn into a motor by the pulsing of the induction and exhaust systems and also by the cooling of a motor after shut down.
    The only way to avoid this happening is to have a dry exhaust cooled by water jackets keeping the water away from possible entry into the motor.
     
  5. gonzo
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    gonzo Senior Member

    There are millions of boats with wet exhaust operating all the time with no problem. Only engines with huge valve overlap may get water in at idle. A crossover pipe fixes the problem.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Wet exhaust systems aren't typically subject to this issue, though it can happen from failed parts. All engines and drives can suffer a catastrophic failure from a part failing, which doesn't have to be exhaust related.

    The late 90's risers on all small block Chevy Mercruisers, are the same used since '86, so it's unlikely there's any significant model run changes, that would make this issue a bigger one than normal. I guess it's possible someone put on the wrong risers/spacers, but this seems unlikely, given how common this setup is.

    Find out what happened, address this issue, then consider a short or long block replacement (rebuilt) or even a whole new crate engine if desired. Prices depend on which engine you have. '95 - '99 engines are one piece rear main seal with the old LT heads (12 bolt intake). A '96 - '05 block is available, also a one piece rear main, but with Vortec heads (8 bolt intake) and these are typically injected. Earlier blocks are available too, but generally a long block is about $1,500 - $2,200, depending on what it is. A long block is a fully assembled and balanced block, with heads and valvetrain and timing gears. It will need the "tin" which can be transplanted from the original engine, as well as induction and other accessories. An afternoon of swapping parts can yield a brand new engine, for a lot less than a turn key crate motor.

    A new (not rebuilt) "dressed" long block will be in the $3,500 to $4,200 range and includes; flywheel, water pump, valve covers, oil pan, timing cover, harmonic balancer and spark plugs. A brand new turn key engine (275 HP Mercruiser Alpha 4V) is about $6,900 (pictured below)

    [​IMG]

    Do these risers look like yours?
     
  7. tom kane
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    tom kane Senior Member

    If you build a fail safe dry exhaust system in the first instance there would be no part failures now with water ingestion.
    Attitude is a killer of innovation." Oh you can`t do that" or "that won`t work". "That does not look good".
    Adding water into an induction engine exhaust is just asking for trouble.
    Just like carrying large volumes of volatile fuel inside your boat along with all of the fuel system parts liable to fail, then ventilating with lots of oxygen (makes things burn) laded air. An accident waiting to happen.
     
  8. whitepointer23

    whitepointer23 Previous Member

    I have had a water cooled manifold with a dry stack exhaust . To noisy but was trouble free. I would prefer a full water cooled system any day.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Dry exhausts have their issues as well, but wet systems are reliable and trustworthy, given reasonable care. Adding water isn't a trouble maker, nor is carrying fuel. These are absurd assumptions, clearly not supported by the facts. Does some percentage of wet exhausts have issues, yep, so do dry. Ditto with fuels, but the statistics just do not bare out these irrational concerns. Nothing is fail safe, nor foolproof, but when a system is developed that reduces failures to fractions of a single percent, well, this is pretty damn reliable and trustworthy.
     
  10. tom kane
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    tom kane Senior Member

    Most modern autos have dry exhausts and are very quiet so there must be no reason why the same can not be achieved in a boat,just a matter of desire innovation and design.
     
  11. whitepointer23

    whitepointer23 Previous Member

    Its funny how people are afraid of petrol powered boats yet i know of more diesel boat fires than petrol. How many petrol powered inboards are in the world. Must be millions. You don't here much about fires. Just have to be maintained like anything else mechanical. I would even swap my perkins for a petrol engine if i got one for the right price.
     
  12. whitepointer23

    whitepointer23 Previous Member

    No doubt at all tom. I think dry works best with keel cooling but everything else runs a jabsco so might as well send the outflow through the exhaust. Quiet and cheap.
     
  13. tom kane
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    tom kane Senior Member

    I prefer petrol or gas personally but why not make it as safe as possible
    instead of using patch ups on an old system.Remember the days when boats had gravity feed petrol tanks under the for-deck or some other risky place.
    You do not hear about the millions of auto accidents until you look.
    Everything we Humans do is the blind leading the blind and we occasionally stumble on a good idea.
    The dry exhaust going straight up gets rid of the fumes better or even out the side like the old launches.
     

    Attached Files:

    Last edited: Sep 23, 2015
  14. tom kane
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    tom kane Senior Member

    Just imagine the thermal efficiency and extra power from those exhaust extractors coupled with extra volumetric efficiency ram induction tubes possible with the first image.
    The second image plan would do away with exhaust fumes associated with transom exhaust
    flowing in behind the boat underway.You could make them much flasher if that is what tickles your fancy.
     

  15. whitepointer23

    whitepointer23 Previous Member

    I have seen standard cast iron manifolds with sheet copper water jackets that worked ok.
     
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