Thanks for the reply.
Yep, salt water and fresh water run every time i pull it out as it sits on a pontoon with winch.
I changed out the manifold 60 hours ago with the new one Merc recommended as it has larger water jacket clearance for salt operation.
Thought about blockage but with the...
I give up! LOL
2012 EFI low emission 3.0L Engine overheats and alarms on the water. Gauge shows about 10 mins past 12 O clock on the gauge. No temps shown just a semi circle from 9AM to 3PM so midday 12 is normal. New impeller December last year. I pulled the thermostat, dropped in boiling...