That makes sense.  But I got to wondering as to exactly what conditions the pump
_and pulley!_ were designed around.  What if, at 5000 or more rpm at cruise, we
have more capacity than we need, and end up pumping a lot of back pressure
against a partially closed thermostat.  A scenario like that would be wasted
power.  If that were so, and we just put a larger pulley on the pump, it would
not absorb as much power, and the lower pump rpm would better match
requirements.  How do we tell if a water pump/pulley configuration is wasting
power trying to over achieve?  Has anyone tried a larger pulley (less pump speed,
less power drain, less flow, but still plenty sufficient for the application)??
Tracy, are you out there??
Inquiring minds need to know .... Jim S.

With the Mazda thermostat setup, as the thermostat closes it recirculates the coolant through the engine.  Probably less back pressure than going through the engine and around the cooling loop.

 

My analysis indicates that you need all the flow you can get for takeoff and climb out.  A larger pulley could get you in trouble.

 

Al G