Water pouring out doesn't mean much. If your exhaust is plugged or
restricted, cooling water can't come into or leave the engine. A
defective water pump could push enough water up to the engine to fill
it but not produce the pressure to pump the necessary volume to cool
the engine. There is no spec. that I know of, but I would guess that
the stern drive pump should pump at least 5 gal. per minuite at idle.
Jim