Please help.Motor keeps locking???

[salzeb]

I have a 16' aluminum v hull with a 99 Merc 25hp 2 stroke. The motor had no issues till 1 day a few kids were stuck on their boat and I (regrettably) agreed to pull them closer to shore. I must have pulled them about 100 yards, less than 5 minutes later as I was cruising the motor came to a complete stop. It seemed like the motor was seized, I couldn't pull the cord. Get towed in, and the marina suggested changing the thermostat, did that and after 5-10 minutes under load it stopped again. Wouldn't turn, got towed in again, took out the plugs, and managed to get the motor to turn, got it started and realized its not spitting water. Had the water pump replaced and tested it for 30 minutes and it was fine. Took it out same day and after 10 minutes under load it seized up again. Has this happened to anyone else? Any suggestions? Appreciate any ideas or feedback.

 

[Chris1956]

Whereas seizure of the engine can be caused by overheat, it can also be caused by a lean air fuel mixture (dirty carb) or low or missing oil in the fuel.

Do you mix the oil with the gasoline or does it have oil injection? If the latter, you should suspect it is not working properly. It probably makes sense to mix your fuel with oil too achieve a 50::1 gasoline :: oil mixture, until you get this straightened out.

 

[racerone]

Towing that boat did no damage whatsoever.----After repeated stoppage ,y you now need to do a compression test.----Post the numbers here.

 

[Faztbullet]

The Merosil block does NOT like to run hot as it starts to shed silica which scores the cylinders. If you lugged engine while pulling boat you could have damaged cylinders or lost a exhaust plate gasket, which would allow water in cylinder and hydrolock it. Either is bad