Not sure about the Nanni, but on our Volvo
, the raw water
also runs through an oil
cooler and a tranny cooler, either of which can be plugged.
Also, worth carefully checking the water
pump">raw water pump again. Just because the impeller is all there, it may have gotten stiff, seriously reducing flow. Also, check the cam (the sorta flat piece screwed opposite the outlet. It can trap debris in the pump inlet, and it is not that uncommon for its holding screw to fail, allowing it to slip out of position and reduce flow. Finally, also check the cover AND the wear plate behind the impeller. If either badly worn can also reduce flow.
As both a diagnostic and a good backup, consider buying
a new or rebuilt raw water pump
and swapping it out for your existing pump if nothing else works.
Yup, been through all of the above at one time or another.