Help Engine Full Of Water
 

Yesterday I was helping a friend repair his Alpha drive. We installed new bearigs an seals in the upper, new impeller in the lower and the bellows.
We ran it on the hose for 15 min or so to make sure it shifted ok then headed for the water.
I back the boat in and he trys to start it. It never fired and locked up immediately. We pulled the plugs and out comes water, most cyl were full.
How could that much water get in without the engine actually running? Its an old boat around 82 260 Mercruser with an Alpha drive, thru prop exhaust.

Did you leave the hose on after you shut it down?

Manifolds rotted out? How old are they?

I took the hose off shortly after shutdown to install the prop. The manifolds are old how can they be tested?

15 min run time is long enough for the thermostat to open and bad head gaskets to fill the motor. check the oil and see how much is in there. this may have been happening for a while.

To test the manifolds pull them off, put them in the vise and fill the water jacket. then heat with a torch and see if the water leaks out.
Old motor may need heads (water jacket corodes around crush point on head )and or head gaskets.

Do you have thru hull exhaust? I have a friend that backed his boat too fast down a steep ramp and water ran up the exhaust. Tried to fire the engine, kicked once with water in the cylinders, bent one rod.

No water in oil. Engine never fired at the ramp. I was with him on his last run and the engine was running a bit hot but never really overheated. He had water in his outdrive oil and toasted a few bearings but I doubt it got hot enough to damage head gaskets. It ran smooth on the hose. This one is driving me nuts. The engine was replaced last year and has about 30 hrs on it.

more than likely, when you backed into the water the exaust flappers did not do there job and let water up over the elbows.
clear the water out of the cylinders and clean the sparkplugs,
hook it back to the hose and get it fired up, if there is a more serious problem it will show it self again.