Don't know what twin VP 431 DPs are. We will assume the engines are
connected to outdrives.

I had a similar problem once. No one could diagnosis it. Overheated
over 1200 rpm. Cooled down at 1100, hot at 1200.

It turned out that the raw water hose connection to the outdrive came
disconnected, just a little, it looked like it was a solid connection.

The result was that it sucked air instead of water when the boat started
to plane. Off the plane, it returned to sucking water.



D wrote:
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