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hydro locked 4.3l mercruiser

guyjg said:
Copy and paste/post it here.
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ok, thanks

boat owner noob here. i bought a 97 bryant at the end of last summer that has been well maintained over the years. the boat has always run great and shown no signs of trouble, other than occasionally running on when shutting the motor off.

i've done a lot of research on the causes of hydro locking one of these motors, and i want to make sure i'm covering all the bases in order to avoid having this happen again.

i had run the motor pretty hard, but idled into the boat slip for a few minutes before shutting it down, so i wouldn't think the motor was too hot to shut down w/o dieseling. when i came back to the boat a few minutes later, it locked up immediately and stripped out the planetary gears on the starter. to make a long story short, i got the water out of the cylinders asap and got the motor running again after having the starter repaired. there appears to be no water in the oil. there was a little water in both banks of the motor. i believing the motor dieseled backwards to suck the water into the cylinders, so i didn't really notice it like it does when it diesels running the right direction for 5 or 10 seconds perhaps.

i understand one of the most common ways to hydro lock this motor is to have a leak between the risers and the exhaust manifolds. if this were the case here, it would seem the motor would also hydro lock when running it on the hose in the driveway, right? there appeared to be no rust on the spark plugs after removing them, if it makes any difference.

i also understand there are measures that can be taken, such as reducing the idle speed and running premium fuel (i'm already using premium because of the running on before that i've encountered), and perhaps retarding the timing a little, and shutting the motor off in gear.

the idea i like most however is to install the anti dieseling solenoid on the carb to immediately shut the butterfly flaps as soon as the motor shuts off.

any help is appreciated. i obviously want to eliminate this problem as thoroughly as possible. let me know if i'm overlooking anything, thanks.
 
the idea i like most however is to install the anti dieseling solenoid on the carb
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Fix the dieseling problem instead of masking it w/a solenoid. The engine must be full of carbon. Merc has a product to eliminate it. Make sure it is timed right and cooling properly. A five minute idle after a hard run is a good thing to do...keep doing it.
 
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