1995 350 mercruiser over heating at wot

"Hello,

I have 95' Rega

"Hello,

I have 95' Regal commdore with a 350 merc alpha 1 drive. The engine runs great accept at WOT, the engine overheats if I keep on plane for to long. Here is a list of info and things I have done to rectify the problem.

- Cooling System: Raw water
- Fresh water use only
- Components replaced: lower unit pickup pump, engine circulating pump, thermostat and all gaskets,

-components cleaned: exhaust headers, engine flushed out, all hoses flushed

I think I have an air leak in the system, at lower engine speeds the pressure in the suction hose connected to the engine circulation pump has postive pressure in it (greater than atmospheric.) As the engine speed increses the pressure in the hose drops below atmosheric, if I had any loose connections air would be sucked into the system reducing cooling capacity. If my thinking is corect how do I fix the problem? Has any one dealt with this problem befor? Any thoughts would be helpfull.

Thanks."

"[b]"- Components replaced

""- Components replaced: lower unit pickup pump,"

Ayuh,...
When you did the Impeller in the Raw water pump,...
Was the old Impeller in good shape, or all torn up,+ missing pieces,..??
If it Was all torn up,+ missing pieces,...
Were All of the missing pieces found,+ removed,..??

My guess the answer is Yes, it was torn up,+ No the pieces are your Problem....
If So,...
Drop the lower unit,+ pull the feed hose off the T-Stat housing,.. Then Back Flush with a garden hose,..."