I'd suspect that Mazda designed the
water pump and flow characteristics to provide adequate cooling for an idling
engine in Phoenix in the summertime. I'd also bet that the
majority of time, a car is sitting at idle, as opposed to cruising down the
freeway at 70 mph.
My suspicion is that the water pump
is designed for some arbitrary flow rate that will be adequate at idle - and at
normal cruise (with it's attendant
increased airflow). I'd guess that the pump is flowing a
much greater volume of water at high RPM's than is really necessary, because
the pump impeller is not variable. The engine temperature does not remain
cold, because the thermostat closes, either completely or partially to keep the
block temperature at 180-deg.
Jack;
The reason a car without a thermostat never
warms up is because it is typically running about 30-40% of rated hp. In an
airplane we are normally running about 70-90 %
I don’t disagree with your flow assessment
for the car; but consider this. My engineering analysis (all the same
stuff that our friend Bill Shertz has now plotted out for everyone) for
designing a somewhat optimum cooling system for my 20B told me I needed 40 to
50 gpm flow rate at 6000 rpm and 260 hp; that range depending on variable
factors. For a 13B that’ something like 22 to 33 gpm. When I
measured the flow rate during the dyno tests I was pleased to find that the
pump produced 48 gpm, with no thermostat, and 37 gpm with a thermostat. This
was pumping thru the engine and through the dyno loop which I know has less
back pressure than my plane’s cooling loop, so my actual flow will be
less.
So I don’t see any excess flow
over what I need at high rpm/power, even running the engine without a
thermostat. Yes, there are regimes where it will be pumping more than I
need – in the same regimes where I don’t care whether I’m
wasting 1 hp driving a bit more flow than needed. And, I could also put
in bigger (heavier) radiators and run a larger delta T and a bit less flow.
(OK, I lied, get on with the beheading –
it’s only because I’m not feeling well and sitting around at my
computer instead of working on the airplane; honest)
Al