Even if the valve was burned. the engine could not push seawater out just by cranking. What concernes me is that if you had seawater in the cylinders, you would have had a lock up due to hydraulic pressure. Then you would have had to remove injectors..spin the motor
..re-fit and hopefully start. It is also possible to bend the conrods if you try to spin the motor
with water in the cylinders.
If you had left the motor for some time the water would have led to a corrosion
seizure. This all leads to trying to ascertain the source of the water...is it fresh or salt
Fresh can only come from heat exchangers..cylinderhead gasket
..cracked block.(very rare)..exhaust manifold..
If you are now running, it wont be the exhaust water cause its getting blown out.
Get the fresh water side pressure tested and see if it maintains pressure.