Engine Overheated & Won’t Start

Put our Moomba LSV with Indmar 340 Assault in the lake to start the summer, but failed to reattach the hoses to the impeller. My son took it out on the lake and it started smoking. He came back to the dock slowly and I attached the impeller hoses. Took it back out on the water and it started smoking again. Realized there was another hose that was detached so I reattached it and turned off the engine. Both nylon exhaust fitting elbows melted and detached. The engine will not crank - it does not even try to start.

So, is the engine seized? Is there a safety/shut-off function that has kicked in? Any troubleshooting tips?

Have you tried to manually turn it over/spin the motor? Did it make any knocking sounds when it was overheating?

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Over heating usually warps the metal and causes dissimmetals to seize. Aluminum pistons will swell and burn out the rings before melt down. The iron block swells at a different rate and the pistons will seize in the block.

Can you remove the sepertine belt(s) and rotate the engine manually using the crank bolt? If it turns over you might be in luck. Also, how hot are we talking 240*F and you might be ok, hotter is an exponential danger. The boots melting is the result of 500+ exhaist with no cooling on the manifolds. This doesn't hurt the internals of the engine but could have caused a boat fire.White smoke is coolant buring, so that is 212+ to boil and create steam.

Your manifolds could be shot from overheating. The inside bellows burn up and water can make it into the exhaust ports and cause hydolock. Your oil is gone if there is any left to begin with. Spark Plugs need pulled and replaced. Try turning by hand then remove the plugs and try to turn it again.

When I was helping a buddy with an older ski boat that was sitting for many years, we did what Holdmybeer mentioned and rotated manually.
Removed spark plugs, sprayed some light oil in each, made sure it was in neutral, and spun the motor manually. Lucky that boat spun.

What does the oil look like?

Did you try to restart when the motor was still hot or cooled down? There would be an engine limp-mode, but not sure if there would be an internal codes from preventing you to try to restart the 340.

Hope you can get it to turn-over. Are you going to try to fix this yourself or take it to a shop?