I have a 1992 boat with twin VP 431 DPs. The boat has about 500 hours on
it. It has a San Juan Eng. FWC
half system and the cabin heater is run on starbord engine. It started
running a bit hot on that side. Back-flushed the raw water intake, good.
Replaced raw water impeller--was not real bad, no missing pieces anyway,
pump looks good. Still same problem, heats under load, cools back down at
low RRM. Changed thermostat, no change. Engine pump seems fine, heater
works, no weeping. Am thinking a restriction in the "out" side of raw
water--manifolds maybe.

Anybody have a suggestion on anything else to check?

Thanks, Dan