8.1 Cooling system flush questions

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by Bwardz50, Jan 7, 2019.

  1. Bwardz50

    Bwardz50 New Member

    15
    Jul 3, 2018
    Lutz, FL
    2006 340 Sundancer
    2005 Mastercraft X2
    8.1 Mercruiser Horizons with V-Drives
    MCX 350 Indmar with V-Drive
    Hi there, thanks in advance for reading...

    I took my new (to me ) '06 340DA out on New Years (water was cold) and once under load, my port engine started overheating. I shut it down at 203° to avoid damaging anything. Long story short, I discovered that the fresh water cooling system had chunks of material around the thermostat from the PO's attempt to fix a leak with a stop-leak product. He ended up replacing the heat exchangers on both engines before selling it to me but there's still residual gunk in the system. I've flushed it with water and a radiator flush & fill kit but there's still crusty stuff stuck to the areas I can reach with my fingers. Temps are now back to normal (155°) under load so I'm happy about that but I'd really like to get this crusty stuff out of my cooling system.

    Does anyone have a recommendation of a product to use that will break this stuff down without damaging the seals, hoses etc?

    Thanks again,
    Brian 20181231_174540.jpg 20190101_171505.jpg 20190101_171511.jpg 20190101_171544.jpg 20181231_174540.jpg 20190101_171505.jpg 20190101_171511.jpg 20190101_171544.jpg
     
  2. Curtis

    Curtis Member

    63
    Feb 6, 2013
    San Antonio, Texas
    320 Sundancer 2004
    Previous 280 Sundancer
    Twin 8.1 (496 Mags) w Bravo III drives
    Yuck.
     
  3. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Did you try flushing it by removing the 2 hex bolts on the block? I would run a hose in the thermostat and flush through the block drains. I would try removing the plug, stick the hose in the thermostat hole and flush. Then put the plug back in , fill and run the engine a bit( idle) , remove the plug and drain. Repeat. When/if it's clean, fill with antifreeze.
     
  4. techmitch

    techmitch Well-Known Member SILVER Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    You are probably going to need some chemical flushing agent help there. Make to use a neutralizer afterwards. And remember, the flushing agent cannot be pumped overboard.
     
  5. Bwardz50

    Bwardz50 New Member

    15
    Jul 3, 2018
    Lutz, FL
    2006 340 Sundancer
    2005 Mastercraft X2
    8.1 Mercruiser Horizons with V-Drives
    MCX 350 Indmar with V-Drive
    I did that to drain the block but this stuff is crusted on. It softens when wet but still sticks around. Need a chemical that I can flush through that will break this up without damaging seals and hoses.
     
  6. Sublimetime

    Sublimetime Active Member

    560
    Oct 22, 2007
    clifton nj
    420 da
    454
    Looks like they might have mixed different types of anti freeze and had a bad reaction.
     
  7. Bwardz50

    Bwardz50 New Member

    15
    Jul 3, 2018
    Lutz, FL
    2006 340 Sundancer
    2005 Mastercraft X2
    8.1 Mercruiser Horizons with V-Drives
    MCX 350 Indmar with V-Drive
    I guess that's possible. I'd really like to figure out what chemical to run through the system that won't damage anything. Thanks for the interest thus far.
     
  8. JVM225

    JVM225 Well-Known Member GOLD Sponsor

    Apr 8, 2008
    Farmingdale, NY
    2002 410 Sundancer, Monaco Edition.
    3126 Cats.
    Prestone makes a “Flush” product. Maybe give that a try?
     
    Last edited: Jan 12, 2019
  9. Spark600

    Spark600 Member

    47
    Dec 28, 2013
    Long Island NY
    29' Amber jack with twin 5.7 Mercruiser and V drives transmission
    Kohler Generator
    Mercury dinghy
    29' Amber jack with twin 5.7 Mercruiser and V drives transmission
    Google barnacle buster how to flush motor
     
  10. sbw1

    sbw1 Well-Known Member

    Oct 10, 2006
    West Michigan
    This is listed in my signature
    This is listed in my signature
    tiara in the snow 01.JPG
    I think you need to be cautious about introducing new chemicals into the system to flush it out. Mixing antifreeze solutions may have cause this although that is speculation based upon what the true facts may be. If antifreeze incompatibility caused this, who is to say a flushing chemical would not make it worse by causing some other chemical compound to precipitate out of solution. If it were my boat, I would contact someone from Dexcool to learn how the mess can be reversed, if in fact in can be reversed.
     

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