Mercruiser 8.1 Hydrolock?

Discussion in 'Sport Cruisers' started by Tacoma290, Feb 11, 2020.

  1. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    259
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    Success! You are spot on, Henry. Tapped the starter with power on, and it retracted. It was done though. Drained all the water from the muffler and used the pump to evacuate all water from the engine. Switched the starter from the other motor and the motor turned. Ran the starter till all the moisture was out. Put the plugs back in and the belt back on. Put the drain plug back in. Took awhile to get it started but it finally caught and ran. Ran it for minutes and checked for steam at the cap: none. Checked the oil: no water in the oil. Ran it for 30 more minutes at high idle. So far so good.
    Thanks to all the folks that chimed in. So much solid knowledge.
     
    Chris-380, techmitch and joeyleggz like this.
  2. joeyleggz

    joeyleggz Active Member

    591
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    Sounds great!! drain the oil anyway refill and take her for a long ride, And maybe change the oil one more time
     
    Tacoma290 likes this.
  3. BillK2632

    BillK2632 Well-Known Member GOLD Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    Good news! That's gotta be a relief.
     
    Tacoma290 likes this.
  4. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    259
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    Yup, change oil, filter, and plugs! Then run it. I may not want to flush the engines again. It may be better just to use the boat...
     
  5. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Exactly, it's a closed cooled motor so not that big of a deal to not flush.
     
  6. Creekwood

    Creekwood Well-Known Member GOLD Sponsor

    Apr 26, 2009
    Oakville and Georgian Bay, Ontario
    '97 330 Sundancer, Raymarine C80 suite with radar, Mercury 310 Hypalon w/8hp Yammie 2stk
    2X 454 carbs w/ vDrives
    You have to run it hot (not at the dock. Running at speed) for as long as possible and change the oil after. You really need to get any water out of the oil. Changes alone won’t do it.
     
  7. DWABoat

    DWABoat Well-Known Member

    612
    Aug 13, 2019
    S Louisiana
    2001 280 Sundancer
    1989 220CC Cuddy Cabin
    Twin 4.3 w/Alpha Ones
    5.7 Mercruiser Alpha One
    I read this entire string of postings like a high speed drama series. You guys are amazing.
     
    Mknupp, kvduff and liv2ryde100 like this.
  8. techmitch

    techmitch Well-Known Member GOLD Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    Couldn't agree with this more. Run it.
     
  9. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    259
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    I did! Ran it fast for a while today. Stopped after 5 minutes on plane to check on the oil. It was not milky, but was a little lighter than I expected. Took off the cap and saw no moisture. The oil pressure was a little lower than the other engine. I am hoping that the lower oil pressure is due to a little bit of water emulsified in the oil.
    I got back on plane for another 30 minutes and it ran strong (amazing that an 8-ton pleasure boat can do 30 mph). Then I tied up at the dock and changed the oil immediately. The oil showed no milk.
    I'll probably take a another fast spin and change it again in the next week, hoping to see more even oil pressures across both engines.
    Once again, thanks for the quick and solid advice, folks. This site is fantastic.
    What a roller coaster, going from moments of asking myself why am I tortured with loving boating so much, to the joy of seeing the engine fire up and rumble. Time for a cocktail...
     
    Chris-380, Henry Boyd and techmitch like this.
  10. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    259
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    Update: Yesterday's goal was to change the oil once more. The engine turned over fine, but it took longer for the engine to start than usual. I hit the on button, waited a few seconds after the beep, then pressed start. The engine turned but didn't fire after 2-3 seconds (the starter did not sound labored), so I turned the engine off and repeated. Second time it fired.
    Once started, it ran solid and sounded normal. Ran it hard in the bay, with no engine alert errors. The oil pressure is the same on both engines. After running hard and docking, I changed the oil again. The oil didn't show any signs of water. I'm a little bothered about the long start.
    I wonder if I need to open the exhaust risers and check/scrape the turbulator plates. If water was in the exhaust it likely fouled them, which may add pressure on the exhaust side. I should have looked for rust after the start, but did not.
    Anything else I need to do?
     
    Chris-380 likes this.
  11. Craig

    Craig Well-Known Member

    782
    Feb 8, 2007
    Maryland
    2006 320 Sundancer
    twin 350 Horizon V drives
    Not uncommon for mercruiser mpi engines to not fire right up immediately. All mine have done it over the years. Think it has something to do with fuel pressure. Someone else may have more insight.
     
  12. liv2ryde100

    liv2ryde100 Active Member

    556
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    Wow amazing post. Who would have thought after that ordeal the starter went bad at the same time. Unreal.
     
  13. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    I recall reading that the 8.1s won't allow the engine to fire until a revolution or two. Thought it was meant to safeguard against hydrolock by not subjecting the engine to more torque than the electric starter can produce. Then again I might have read this in a dream too...o_O
     
  14. Korkie

    Korkie Active Member GOLD Sponsor

    768
    Feb 2, 2016
    Leonardtown, MD Potomac River / Chesapeake Bay
    340 Sundancer 2006, Garmin 7612, xHD Radome
    Merc 496 Mags
    Bravo III Drives
    Definitely a priceless story. Wonder what this scenario would have cost if Tacoma290 would have just call in a Merc mechanic and told them to just fix it? Thousands I bet.
    Wonderful thread!
     
  15. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    I have a question. Did you flush the engines without them running? Just wondering, because I have a flush system similar to the perko and always flush with running. Once i'm done flushing I shut off the engine then turn off the water within 5-10 seconds.
     
  16. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    259
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    I flushed them running. But the timing for stopping the flush is critical. To stop the flush, normally one turns off the engines, then stops the flush water. I recall that Mercruiser says to not run the flush without engines for more than 15 seconds. Your 10 seconds are a much better number and leave a safety factor.
    My marina is 10 minutes from home and 10 minutes from work, so I now simply run the engines once a week, and am avoiding the need to flush.
     
  17. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Thanks. I have 2 safety features. I plumbed my flush right before the strainer. When I turn on the water it comes out the seacock grate. Once I start the engine it pulls in the fresh water. When I shut it down the water comes out the bottom. Hard to explain, but I'll never have that problem. Look at my thread..

    http://www.clubsearay.com/index.php?threads/new-flush-system-installed.87193/#post-984386
     
    Chris-380 likes this.

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