Does This Debunk the "Coolant Can Flow Through the Radiator Too Fast" Idea???
Water pump uses centrifugal force to create a low pressure area.
This is not a positive displacement pump, vanes/flukes are not sealed to the case/housing.
No "pressure" as such, is created, only circulation.
The lower rad hose, the return heater-hose, and by- pass hose all channel coolant into the center chamber of the pump/impeller.
The impellers centrifugal force flings coolant outward (creating low pressure) to the channels thru the timing cover to the block, distributes thru the block/heads, to the engine outlet to the top of the rad, sheds heat thru rad.
Then sucked back to the center of the water pump, repeat
Some newer systems often require air to be bled from the system to get coolant circulation.