1999 Mercury 50hp 4 stroke overheating

[Boat guy]

engine overheats and alarm goes off at all speeds, dealer installed oil pressure & temp sensor, new water pump impelller and base plate & thermostat. Still overheats. Dealer said motor has blockage. I removed powerhead blew compressed air through entire block. I replace 4 anodes in the head and also felt air coming out of each head with anode removed while blowing air through the head. Re-installed block and still overheats. While the lower unit was off I hooked a hose directly to intake line. I tried to duplicate hose pressure vs normal impeller pressure. Motor did not over heat? I'm at a loss what is next. This is the year where Mercury used the Yamaha powerhead. I heard of the intake line getting clogged under the adapter plate? Also I heard of anodes breaking off in the Yamaha engines and clogging the water passages. any thoughts thx

 

[mechanicman]

If it didn't overheat on the hose. Then I would take a closer look at the impeller. Maybe they forgot to put the keyway back in

 

[Boat guy]

If it didn't overheat on the hose. Then I would take a closer look at the impeller. Maybe they forgot to put the keyway back in

I replaced the complete water pump again no luck key is there thx