Agreed, the suck it up via the outdrive method does not work because of the nature of raw water cooling. With a cold engine, the stat is closed, all the water from the impeller will exit the exhaust elbows. As the stat opens, some water will exit the engine, but the stat will rarely stay open all the way when the engine is on the water hose idling because it does not build enough heat in the cooling water to keep the stat fully open. So, you see AF exiting at the outdrive but that does not mean that ALL the water in the block exited and is replaced by AF.
The other issue as I have said before, these engine blocks (cast iron) were designed to be used with a pressurized cooling system with antifreeze with corrosion inhibitors. Using them as a raw water-cooled system results in rust flakes that can clog passages and drains, and also in shallow water silt, mud etc can cause the same problem. Cast iron and aluminum corrode differently, the way cast iron corrodes tends to clog cooling passages. Aluminum pits but does not shed flakes like cast iron.
