It sounds as if you have looked at most of the usual causes. The
symptoms sound very much like what can happen with Zebra Mussel
infestation throughout your cooling system.
Was your boat left sitting unused in the water for a couple of weeks? If
so, that's all the time it can take for a colony to grow large enough to
clog your system. For your sake, I hope that you find a simpler
explanation for your problem, because the Zebra Mussel problem usually
calls for a tear down in order to get rid of the little devils.
Good luck and good boating,
Jim

saltare wrote:
I have an 85 Supra Saltare witha PCM 454 Chevy inboard engine that is
overheating as soon as it gets revved over idle speed. I have replaced
impeller, thermostat, and water pump with no change. I know the hose is
clear from the impeller to the water intake under the boat, because I ran
water from the impeller down to the water intake, but it doesn't appear to
be taking the water in up to the impeller. I checked this by unhooking the
hose from the impeller to the thermostate housing and its not getting any
water. I know the impeller is turning i.e. turning gear operates correctly
and belt is not slipping. I am at wits end. Does anyone have any ideas?


Thanks

Saltare