Originally Posted by Minnewaska
I still find an intake blockage to be the least likely, but good luck. Could happen, I suppose. If you don't already have wire reinforced clear hoses, you might consider replacing them while you're at it. Much easier to see flow when the engine is running and to eliminate the blockage theory.
Good Point. My hoses are just standard black engine cooling hoses. I considered installing wire reinforced (that is really what a suction hose should be) but the ones I have seemed to have worked well. Maybe the hose is colasping when the raw water pump is pulling suction. I will check this.
Good point as everything may show up clear- but the hose collapses when you run the pump. Maybe that is the problem the OP is having. At idle the suction would not be enough to collapse the hose, but at high rpm the suction increases on the suction hose and the hose could collaspe.