For those of you that do not want to read any further, it's fixed. For the rest of you, here is the saga.
I took off the hose from the thru hull
and the water
flowed freely. I put the hose back and took the top off of the strainer, water flowed freely. Everything else is above the water line, so I put a hose from the washdown pump to the hose coming off of the strainer and water flowed freely all the way to the pump. Also there were no leaks
between the strainer and the pump. But this was under pressure not suction. As it happens I have a small manual vacuum pump on board (I have Way too much stuff on this boat). So I found a fitting and put it into the end of the hose at the pump and pumped the hose full of water. When I stopped pumping the pressure held at -3.5 inches of Mercury
(iM). This is about right as the end of the hose was about 40 inches above the water line. It held that vacuum for 10 minutes, so no leak in the intake system. So it must be the pump right. I plug
the outlet and pull 25 iM vacuum on the pump. It holds!, no leak in the pump (hold that thought). I then put the vacuum pump on the outlet of the pump and pulled the prime all the way through the pump and into the outlet hose. It pumped what was in the pump and the outlet hose and stopped. I thought it must be the hose to pump connection, so I trimmed off an inch of hose to get on nice clean rubber. No change. put in another impeller and still no change. By this time i'm in insanity mode, that is repeating the same things over and over again expecting a different result. I tried disconnecting the outlet in case things were blocked on that end and still no change. It would empty the water out of the pump but that was it. It seemed it had to be a suction side air leak but the vacuum pump tests said no. I was talking to a friend of mine and he said maybe you have a bad bearing. It wasn't obvious, but that is what it ended up being. I took the pump apart and the shaft had about 1/32 of play radially. The bearing had indeed gone bad, even though it wasn't making any noise
that I could hear. It so happened I had kept many of the parts
to my old water pump when I replaced it with this one two years ago. The shaft and bearing assembly from that one had no play in it at all. I took the new pump hosing off the mount and put it on the old shaft/bearing. It now pumps water. Apparently that small amount of play caused an air leak at the shaft seal
but only when at operational speed. The static testing showed no sign of it.
I suspect I might have the belt too tight and it caused the wear in the bearing. In any case I see a new pump in my near future but am operational for now.