Engine over temp at idle
Went out for a sail Saturday and when returning to the slip I left the engine running at idle until I had the boat secured. (This is something I always do) While idling the temperature started to rise above normal and quickly went back to normal when I increased the RPM. Not sure what to look for. I have not changed the impeller yet this winter. I have cleaned the sea water intake filter. Engine is a Universal 12hp diesel. Any recommendations?