Water pumps are not positive displacement pumps.
Correct.
The water pump is a centrifugal pump
Correct.
that can move a large volume of coolant
Correct.
without increasing the pressure of the coolant.
NOT correct. OF COURSE there's a pressure differential between inlet and outlet.
The pump pulls coolant in at the center of the impeller. Centrifugal force throws the
coolant outward so that it is discharged at the impeller tips.
Correct.
You guys understand that fluid under pressure is equal through out the system correct? 15 PSI is 15 PSI in the ENTIRE system ,NOT 15 PSI on one side of the restriction and a lower pressure on the other side of the restriction.
ABSOLUTELY TRUE but only if the pressurized fluid ISN"T MOVING/flowing. This is true ONLY in a static system.
A restriction does nothing to lower pressure
ABSOLUTELY TRUE in a system where the fluid IS NOT MOVING. NOT true in a system where the fluid is flowing through the restriction.
it only slows down the flow. The reason that GM put the restriction in the system is they changed the way coolant flows through the block
Yes. Instead of pulling heated coolant from the back of the cylinder head, directly into the intake manifold right-rear corner, they restrict the gasket so the coolant has to flow forward in the cylinder head to the thermostat crossover, then from the thermostat crossover under the fuel/air runners in the intake, to that same right rear corner of the manifold where the quick-coupler is. This forces coolant to flow under the intake manifold, keeping it at a uniform, warm temperature. Or, in other words, the intake manifold is heated by engine coolant that is then routed through the heater core.
and they needed to slow down the coolant so that it would pickup heat from the block.
NOT true in a closed system, where the coolant just recirculates. There may be some extreme cases where insanely-high flow doesn't pick up heat, but we're talking ordinary automotive systems, not some laboratory experiment.
OF COURSE there's fluid pressure differences in a system where the coolant is MOVING.
If the engine were shut-off; the radiator cap will retain pressure while the engine is warm. The pressure is the same everywhere. This is called static pressure.
As soon as the engine starts, the water pump moves coolant; the coolant won't move unless there's a pressure differential--high pressure on the water pump outlet, low pressure on the water pump inlet. This is dynamic pressure.
With a running engine, you have dynamic pressure superimposed on the static pressure.
Consider an air conditioning system: the thing won't work unless there's a restriction (expansion valve, orifice tube, or something else) that creates a restriction downstream from the pump (compressor). The restriction drops the pressure, it's the "dividing line" between the high-pressure side and the low-pressure side of the refrigeration system. The "low side" is cool/cold, the high-pressure side is warm/hot. Don't tell me that restrictions don't drop pressure, 'cause you can see it with a manifold gauge set. The "high side" can be over 200 psi; and at the same time in the same system, the low-pressure side is going to be 35--45 psi. Shut the engine off, and eventually the pressure equalizes to perhaps 70 or 100 psi (pressure higher or lower depending on ambient temperature.)
Water pump is not any different, although the system is more complex in that there's not one major restriction in the cooling system. There's all sorts of minor restrictions, among them the radiator core and the heater core. Every casting obstruction in the engine is a small restriction, with it's tiny effect on system dynamic pressure.
