New to me 1975 Johnson 15HP Help Please!

[pizbrewin]

Hi guys! Newbie here. Just picked up a 75 15HP. I think it's overheating because when I spritz water on the block when it's running the water boils off. What do you guys think impeller? Never took anything like this apart - bikes and jetskiis yes. Outboards not yet lol! Thanks in advance.

[boats.net]

Yes, start with water pump impeller. If continues, check thermostat.