Hi , I had this problem on our
yanmar last year alot of
water coming out. You need to take the pump off {in our case this required taking off the
engine mount} you will most likely find it is the "mechaical seal" that is the problem ,this is a ceramic seal with a spring they are about $20 to $30.
Call Johnson pumps and give them the pump no which will be on the outside of the wear plate. Beware the
rebuild kit can sometimes be almost the
price of a new pump .
Good Luck.