just bought a 99 nitro w/115 merc 4cyl 2+2 engine, runs out awsome, but on lakes with lots of muck and millfoil it overheats> alarm goes off, water still comes out pee hole, let idle and it cools off then it's fine? going to replace water pump but don't know the best way to do this? have done others but on smaller motors> just don't know what all i need to disconect to drop lower unit? on clean lakes this does not overheat? any other info would be great! does anyone know what part numbers i need?