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Mhans

? Hydrolock Merc 8.2 Sunesta 264

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Have a 2011 Sunesta 264 w/Mercruiser 8.2..

Was running perfectly all year. Took it downriver for lunch. No problems at slow or fast speeds.. Docked at slip for a couple of hours. Came out to leave. Turned key on and 2 long alarm beeps. then they stopped. Nothing displayed on dash. Started without a problem..first crank. Took off back home...9 miles upriver. Worked flawlessly...slow through N0-Wake zones and 3/4 throttle back to dock. Pulled into dock without incident. No overheating...No "limp mode"...nothing seemed out of the ordinary. Tied up for 1 hour. Went to start the boat and started to crank and immediately "clunked" to a stop. Every attempt to turn it over would either briefly make a normal cranking noise, but quiclky freeze to a complete stop. Batteries are new....12.5-13v output. No change with Battery selector on 1-2-or both. All accessories work fine.

When key turned on, sea water temp only 120-130 degrees. All fluid reservoirs/oil levels perfect. Engine still seems "seized"....after the perfect run back from lunch. No alarms.

I have lived through a hydrolock before when an impeller was cooked along with exhaust flaps. That followed a clear overheat situation. This time...no warning...boat was running fine...and problem occured on attempted start up after sitting for an hour.

Any ideas? First plan to pull plugs and try to manually crank engine...

Thanks

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going to say to help rule out hydro lock youll have to check plugs.

But to be honest Im thinking more electrical than anything. Check all connections and I mean all. battery to starter, to alernator. You also might be looking at bad starter solenoid.

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If it appears to be locked up, carry a breaker bar and 7/8" deep socket along and try to turn it over by hand. If it's locked try turning it over counter clockwise. If it turns easy then she may in fact have water in a cylinder or two. Check your coolant level in the surge tank first to rule out a blown head gasket. If it's sea water, then you may have an internal gasket weep in the riser, elbow joint allowing sea water to back track down into the cylinder head exhaust port. As Soldier said, pull the plugs and then crank her over and look for water being expelled.

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Were you tied up with stern facing lake getting wakes and waves slapping against it? That could have forced the water in cylinder.

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Pull the plugs crank over until all water is out, then spray or fog each cylinder thoroughly It's prob what wingnut had said. Gaskets on riser or manifold

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Were you tied up with stern facing lake getting wakes and waves slapping against it? That could have forced the water in cylinder.

Are you telling us that you have really seen this or is this speculation? learn something new here ever day, but I've thought about this as a possibility and just cant get my head around as to how this would be possible based on the riser and raw water circuit configuration.

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Wing,

Speculation for his condition as he described in initial post. "Ran fine all day, no issues" only thing he did was tie up at a dock for an hour. Possible worn exhaust flapper...Exhaust valve open via cam shaft position. Water surging towards back and slapping into back of boat has enough pressure to push water back thru the exhaust. It's happened to quite a few people while launching boat and backing into launch to quickly. If I'm not mistaken the big block is affected more than others due to riser height. Haven't seen or heard of this issue on a small block merc.

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Wing,

Speculation for his condition as he described in initial post. "Ran fine all day, no issues" only thing he did was tie up at a dock for an hour. Possible worn exhaust flapper...Exhaust valve open via cam shaft position. Water surging towards back and slapping into back of boat has enough pressure to push water back thru the exhaust. It's happened to quite a few people while launching boat and backing into launch to quickly. If I'm not mistaken the big block is affected more than others due to riser height. Haven't seen or heard of this issue on a small block merc.

OK now I better understand. I suspect that the angle and subsequent deep immersion during launch along with the fact that the raw water side of the cooling system is dry could facilitate the described reversion. I don't however feel it would be possible if the system was static and wet as the head pressure would have to be overcome by the wave action. As the risers represent close to 3' NPSH, then the wave would need to exert in excessive of 1.5 PSIG in order to break the stalemate. Not saying it isn't possible, but the wave would have to be higher than the transom I suspect.

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