My Volvo penta 5.7 engine started overheating, at speed and idle. I replaced the entire raw water pump assembly. When I attach a water hose directly to the engine flushing bib, I get water out of the exhaust and everything seems to work properly. Engine runs fine. However when I put the boat in the water, at idle it immediately over temps and runs hot, 210 degrees. I have not been able to find any posts that suspect a water circulation pump may be at fault. Any suggestions?

 

I am thinking of the sea water pump or clogged collector

 

That engine does have a thermostat to regulate the engine temp (in the normal thermostat housing)