In the interest of saving some fellow boater a trip "down a rabbit hole", I offer. My 1995 Santego 5.7 TBI had overheating problems, especially at idle in long no wake zones. After impellers (several), one new / rebuilt, raw water pump, professional heat exchanger cleaning, new thermostats - I finally got serious about pulling some hoses and troubleshooting. It appeared that the engine coolant circulating pump was weak (no noise, no leaks). So I hustled on down to Carquest and picked up a replacement for about $50 and a couple gallons of antifreeze. Port engine now rock steady at 170*. Starboard replacement pump is now in hand and going in ASAP. I hope this is helpful to somebody.