Mercruiser 8.1 Hydrolock?

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

  1. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    248
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    Need help on how to protect the block.
    Came back from a day trip on Sunday. Engines ran solid. Shut them down. Came back the next day to flush with these:
    [​IMG]
    While the flush was going, the port engine would not start. Stopped the flush. Smartcraft said Port MAP input Hi. Thought the sensor was bad and that battery was the issue and used the emergency start (in hindsight perhaps not the best move), but the port engine would not turn over. Called it a night.
    Now I am thinking hydrolock, and that the pressure of the water during flush may have overwhelmed an exhaust gasket, or the gasket failed when the engine was shut down. And that the MAP sensor was correct. Will pull plugs and check oil today. Have read to add Marvel mystery oil to the 'wet' cyclinder(s) assuming that there is water in there to prevent rust.
    Questions: How would this oil be added to the cylinder since it is in a bottle? Is there some other spray in oil to be used?
     
  2. Air O'Nautical

    Air O'Nautical Active Member

    Feb 5, 2008
    Stamford CT "Ponus Yacht Club"
    1995 400EC. Raymarine E80,4kw dome, Garmin 235 gps,
    2013 7.4L Mercruiser Blue water.
    Hurth straight shaft 630's,
    Westerbeke 7.0 BCG
    You could be hydro locked!
    You need to pull all the plugs immediately. Crank the engine over to expel water out of the cylinders.
     
  3. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    That ^^ and change the oil, go run it hard, and change the oil at least 1 more time.
     
  4. Air O'Nautical

    Air O'Nautical Active Member

    Feb 5, 2008
    Stamford CT "Ponus Yacht Club"
    1995 400EC. Raymarine E80,4kw dome, Garmin 235 gps,
    2013 7.4L Mercruiser Blue water.
    Hurth straight shaft 630's,
    Westerbeke 7.0 BCG
    Forcing water under pressure into the raw water intake line can fill the exhaust system to the point that it backs up into the engine through the exhaust valve.
    The exhaust “pulse” or pressure of a running engine is necessary to force the water up and out of the water lift muffler.
     
  5. KevinC

    KevinC Well-Known Member

    Feb 25, 2011
    Long Island, NY
    2004 340 Sundancer
    Twin 8.1 V-drives
    If I remember correctly it is recommended that the flushing be stopped within 15 seconds of the engine shutdown. From the Merc Manual for inboards:

    upload_2020-2-11_12-48-57.png

    -Kevin
     
  6. Bt Doctur

    Bt Doctur Well-Known Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    Pull the plugs and drain the cylinders
    restart the motor , you must run it TO NORMAL TEMP for about an hour or so.
    For long term storage, hook up a remote tank with a gallon of gas, 1 pint of 2 stroke oil, 3/4 pint of Sta-Bil . Run till it smokes
     
  7. BillK2632

    BillK2632 Well-Known Member GOLD Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    [QUOTE/]
    Have read to add Marvel mystery oil to the 'wet' cyclinder(s) assuming that there is water in there to prevent rust.
    Questions: How would this oil be added to the cylinder since it is in a bottle? Is there some other spray in oil to be used?[/QUOTE]
    Use an old fashion oil can if you have one, a turkey baster or a gearlube pump (the ones that screw onto a bottle). You can also use a spray can of fogging oil - even wd40 - at this point the urgency is to get the water out and something in the cylinders to prevent rust from setting in. Then change the oil and get the engine running.

    Almost certain that running the flush water without the engine running filled the lift mufflers and backed water up through the exhaust.
     
    Last edited: Feb 11, 2020
  8. Sublimetime

    Sublimetime Active Member

    791
    Oct 22, 2007
    clifton nj
    420 da
    454
    If you have water lift mufflers and you filled them you should drain them too.
     
  9. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    248
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    Update: pulled the plugs. Water in three holes. Sprayed the holes with WD 40 first then all holes with fogging oil. Drained water from the exhaust runners where they connect to the muffler. Trying to use a breaker bar to turn the crankshaft over with the plugs out The only thing that moves is the nut on the pulley by a small amount. Bar is maybe 24 inches. Bigger bar? Anything else I should look at?
     
  10. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    With the plugs out that should spin easily with a 24” breaker bar.

    I wouldn’t use any more torque until I knew how big the crankshaft bolt is. Don’t risk breaking it!

    I’d wait for Someone with more 8.1 experience will chime in.
     
  11. rmlsll

    rmlsll Active Member

    178
    Oct 11, 2009
    Saugatuck MI / Cape Coral FL
    340 Sundancer 2004
    24' Avalon Tritoon 2019
    10' Zodiac
    Twin 8.1 Mercruiser V-Drive
    150 hp Mercury outboard 4 stroke
    Did you drain / change the oil ?
     
  12. 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
    With the plugs out, will it not turn over with the starter?
     
  13. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    248
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    Not yet. The oil shows no milk. I feel more pressure to get the motor turned over, then oil change.
     
  14. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    248
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    I’ll try that next, but worried about the starter. Will switch the starter from the other engine. But I feel like I need to clear all the water from the exhaust. If flushing filled the exhaust side with water, is it possible I need to do more on that side before toasting a starter?
     
  15. BillK2632

    BillK2632 Well-Known Member GOLD Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    That doesn't sound good. How long did the engine sit with water in the cylinders? Without the plugs in it should spin easily with they key/starter or a breaker bar. So, either things rusted up in those 3 cylinders or something broke when you tried to start the hydrolocked engine. Fill the cylinders with MMO or PB Blaster, let it sit overnight and give it another try. If the starter won't turn it, use the breaker bar to rock it. If none of that works, unfortunately I think something big broke.

    Don't worry about water in the mufflers at this point, with the plugs out you can't hurt anything - ie the engine can't be hydrolocked with the plugs out. If the engine will start, it will blow the water out of the mufflers.
     
    Last edited: Feb 12, 2020
    Craig and techmitch like this.
  16. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Your not going to toast your starter with the plugs out.
    You need to get that engine running asap. It's only been a couple of days, not going to freeze up from rust that quick
     
    joeyleggz and techmitch like this.
  17. Tacoma290

    Tacoma290 Active Member SILVER Sponsor

    248
    Oct 5, 2006
    Tacoma, WA
    340 Sundancer 2007
    Twin 8.1S V-drives
    I'm still troubled that I can't turn the engine on a breaker bar by standing on it with the plugs out. I agree with Scottlaw that rust should not have taken over in 2 days (flush was on Monday). Could be something inside that failed. My mechanic suggested another possibility that perhaps the starter is stuck in the engaged position. I'll pull the starter, move the old one over, and meet with one of his techs.
     
  18. BillK2632

    BillK2632 Well-Known Member GOLD Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    Let's hope that is the problem. Agree rust couldn't set in that quick. Even if something big bent or broke, I don't think it would completely log up the engine, seems would move, might even start just make a bunch of noise.
     
  19. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    It's not in gear is it ?
     
  20. Henry Boyd

    Henry Boyd Well-Known Member GOLD Sponsor

    Apr 24, 2007
    Newburyport, on the peaceful and serene Merrimack
    ‘09 Sabre 38 Hardtop Express “Serenity”
    Volvo D6 w/IPS450 Pods
    I'm not sure you are going to be able to pull the starter. You may have to tap the starter housing to jog the drive into retracting. Since you probably also won't be able to get near it with a hammer, you can use a metal rod/bar to contact the starter housing and then hit the free end with a hammer (went through a winter semester with an old chevy with a bad Bendix drive).
     
    Tacoma290 likes this.

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