Probably the head gasket on the exhaust side.

jamesgangnc wrote:

I'd share your fear.

The impeller looks good? I would not expext the bend in the prop shaft
to affect the cooling.

What kind of engine?

bob wrote:
I have 1998 Glastoron Se175 that I thought I got a great deal on. The
2nd time the boat was taken out it overheated to the point it warped a
valve and melted my wiring harness. I tore it down and had the head
machined/valve job and rewired the unit. I replaced the nub, where the
impeller used to be and the thermostat. After extensive time on the
unit, I got it running very well in my driveway with the mufflers on.
When I take it out, it runs very well, but runs very hot at high speeds
190-205. The guy that owned the boat before me took out the overheat
horn. When I cut the speed to 3000RPM the temp drops back to 180s.
If I sit and idel for ~2-3 minutes the temp drops to the 140-150 range.
After close inspection (I bought the boat w/o seeing it for $3700 when
it should have been worth about $9k), I notice the prop shaft was bent.
Could the eleyptical rotation of the shaft be causing enough water
interferance/low end shacking that the unit cannot get water at high
speeds? I will replace the shaft, but fear the problem will remain. I
ideas on the overheating issue and suggected paths to resolution?