Agree. Water pump is dual functioning....at low speeds acts like a displacement pump....blades touch the walls of the eccentric chamber starting with a large volume and compressing to a small volume as the revolution completes, developing the water pressure.
At high speeds it acts as a centrifugal pump with the blades folding back (detailed in published data...forgot source), and with the incoming water pressure via the water inlet ports on the LU...shaped as they are, just like on a jet aircraft to scoop air, they scoop water, the pressure increases. By folding back, the water pressure is variable/soft, even though it's 3x idle pressure roughly, and nothing blows up like would happen in a hydraulic system with a displacement/reciprocal pump requiring an over pressure regulator to protect the system.....or something to that effect.
Your "ram water" at WOT, which is limited at 50% throttle setting is masking the worn impeller. (opinion)
