Sealers seldom work on a closed cooling system. The chances of it
working on a raw system in a boat are zip. They need to get hot and
circulate around in the cooling system for a while if they are going to
even have a chance at working.

Did the head gasket look ok when you disassembled? You should also
check the top of the block with a straight edge. Any events leading up
to the problem like overheating? Did you winterize last time? Was it
leaking at the beginning of the season or did it start in the middle?

Engine blocks very seldom crack from normal use.

wrote:
Twice I have replaced head gasket thinking water was leaking into oil ,
last time did pressure test and checked plane on head , head was fine
which leaves me with a crack in the water jacket , has anyone tried
putting sealer in , and with a external water source how do you put it
in .
Any help would be greatly appreciated
Paul