I don't know specifics of that year but have you checked the heads and gaskets? Also if there is a seperate water passage cap (terminology ???) pull it to see if there is a hole through the head. Is it a salt water motor???<br />Hope that helps.
Tazman is correct. Head gasket and the word he was lookin for is "exaust port plate" gaskets. Each has water jackets all around combution and exaust jackets. A gasket leak would cause this. Of course, don't rule-out a cracked (eeewww) block.<br />You will need the manual for sure on rthis one.
