Um, Is The Pump Impeller OK?
If you are sure, the problem may be in the outlet for the cooling flow indicator. I know that Tohatsus, in their 2.0 to 5.0 sizes, and their generic twins, are subject to salt water clogging. My guy just drilled out to a larger size the nib that the hose attached to for more flow. Otherwise, just try running a piano wire into it to clear any deposits. Rick D.