TOPIC: Johnson 35 over heating

This may be a bit OT but gonna ask anyway ! buddy of mine brought a boat to me. A relative of his neighbor gave them a boat with a 2000 Johnsoon 35 on it , reason being it kept overheating and hed had enough ! I changed the impeller which was almost new , thermostat when I took it out was in pieces and half melted so ... I got a new one and put it in . IT IS GETTING WATER TO THE HEAD and just in case it was a oil pump issue I have it running on pre mix , with in minutes of starting temp alarm went off , thermostat housing gets hot enough you cant touch it , took the remains of the old housing cap and screwed it in and temp went down .. Im reading on the internet these engines have a problem , any ideas out there ? Thanks Dave