high speed miss when hot.

[xltier]

have a 3.0-93 omc that starts to breakdown when it runs for about 15 minutes at high speed.if it cools off a little then it goes again for a while.its turning 4,000 when it right.I also noticed tht the large hose going to the circulator pump is warm.i would think it would be cold.i changed out the thermo-stat but that didn't help.any ideas,i also replaced the plugs-wires-cqp and rotor-coil.tried it with the interrupt disconnected also.

 

[southkogs]

Impeller?

 

[xltier]

its new.I am getting pressure somewhere in the cooling system.if I pull the big hose off at the thermo housing it sprays out instead of drawing down.should that hose be hot?it kinda pulsas pressure then not.checked the pump[circulator] its fine.riser is fine.can it be a head gasket with good compression.?