My BIL owns one. Starboard engine is running hot anything past idle. We checked the thermostat and it is opening. The boat was in salt water most of it's life and now is in fresh. We are thinking perhaps the risers need replacing. Any guidance as to what risers and spacers should be ordered?

Sounds like a water pump impeller issue. When was the pump last rebuilt?

I don't know when the impellers were changed last. Both engines flow the same amount of water at idle. I imagine both pumps should have the impellers replaced. Naturally, the starboard engine is the hardest to access.