Mercruiser 4.3L water in oil

Dynasty190

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Joined
Aug 14, 2009
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I have a mercruiser 4.3L I/O and a few days ago I had the boat out. It was running fine at around 3900 rpm and suddenly it developed a knock and started having excessive blow-by from teh valve cover vents on top. The engine still had oil pressure, but had a knock that didn't get louder with increased rpm, but got faster. I have no idea what to do first, but would appreciate any advise
 
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