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  1. #1
    Cadet
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    Jul 2003
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    Default Mercruiser 7.4 litre water in oil

    I have a 1992 mercruiser 7.4 litre in a celebrity 230 bowrider. It has only been used in fresh water. It has standard thru the hub exhaust. I have a mechanic winterize it each year, but do not believe he did so last year. I started and ran it with muffs on and everything was o.k. 4 hours into my first boat trip this year everything was perfect until the alarm went off. The engine was at 200 degrees, and I immediately shut it off. Up to this point the engine ran perfectly. I pulled the boat back to the dock at 5mph. Ten minutes after I had shut it off, I attempted to crank the engine and it would not turn at all. The next day I pulled all 8 plugs and found cylinders 3-4 hydrolocked. I blew out all the water, fogged the intake and cylinders. Two plugs were dry 6[/LIST]were wet. I cleaned and reinstalled the plugs. After cranking for a while the engine started and ran fine but I couldn't get any water to go thru the engine. I found that the seawater fuel pump had destroyed the impeller. I replaced it and found all the old pieces in the pump output hose and th p.s. heat exchanger. Started the engine all was o.k. except the oil was coffee with cream colored---i.e. full of water. I drained it and refilled it ran it for 10min. again coffee with cream for oil. I drained and refilled again (the only way I can do it is thru the dipstick tube) and this time the oil stayed pretty clean. The color was still a tad off so I changed it again. I am looking for suggestions as to what caused the hydrolock. The engine was off when it occured. Additionally, the original h2o pump lasted 8 years and 400 hours, the second 3 years and 40 hours. I saw no evidence of dryrot on the impeller blade remains. The flappers in the exhaust have been replaced 3 times, and I guess they are still working. So, how did cylenders 3-4 (which are on opposite banks but in sequential firing order get full of water and what weird chain of events caused this? If the block was cracked or something along those lines wouldn't it be misfiring on a cylinder or two?

  2. #2
    Seaman
    Join Date
    Jul 2003
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    Tualatin, Oregon
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    51

    Default Re: Mercruiser 7.4 litre water in oil

    Original exhaust? COuld be a crack in the manifolds.

  3. #3
    Chief Petty Officer
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    Oct 2002
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    ketchikan alaska
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    Default Re: Mercruiser 7.4 litre water in oil

    overheated engines often diesel when shut down. sometimes backwards sucking water up tailpipe. second scenario is 3 and 4 exhaust valves were open and as engine cooled down it pulled enough vacumn to pull some water up the pipe. vp and merc are putting vacumn breaks on some of thier engines. third is you just hauled back throttle real fast and shut down engine when alarm went off. with enough headway your own wake could have hit the stern and forced water past the flappers. or the leak thing.

  4. #4
    Commander magster65's Avatar
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    Sep 2002
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    Default Re: Mercruiser 7.4 litre water in oil

    Good thoughts. I think a fella should pop the risers off and have a looksie in the manifolds every year just for the piece of mind. Gaskets are cheap.
    Arrr matey!
    2002 3788 Bayliner "Motley Crew"
    Twin 270 Cummins

  5. #5
    Cadet
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    Default Re: Mercruiser 7.4 litre water in oil

    Thanks for the replies, the engine was at an idle when shut down, I will pull the risers and check the manifolds, I noticed noone said cracked heads block or headgasket...David

  6. #6
    Chief Petty Officer
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    ketchikan alaska
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    Default Re: Mercruiser 7.4 litre water in oil

    thats because your first post made it sound as if no new water was getting in oil so assumption is oil leaked past rings from hydrolock.

  7. #7
    Seaman
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    Tualatin, Oregon
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    Default Re: Mercruiser 7.4 litre water in oil

    I'm sure David is glad no one mentioned those things!

  8. #8
    Cadet
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    Chesapeake Bay
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    Default Re: Mercruiser 7.4 litre water in oil

    David:When it was all said and done, what wound up being the problem?

  9. #9
    Chief Petty Officer
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    wilmington N.C.
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    Default Re: Mercruiser 7.4 litre water in oil

    Static line too low.

  10. #10

    Default Re: Mercruiser 7.4 litre water in oil

    I have EXACT same problem, water in oil, please let me know what the bottom line problem was, thank you, Dave

  11. #11
    Rear Admiral Fishermark's Avatar
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    Default Re: Mercruiser 7.4 litre water in oil

    Quote Originally Posted by Dave Blurton View Post
    I have EXACT same problem, water in oil, please let me know what the bottom line problem was, thank you, Dave
    Hi Dave. Welcome aboard!

    This is a post from six years ago - and note that the original poster only posted twice. I don't think he will see your question.

    Best to start a new post of your own and describe your problem.

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