This seems to be the big question.  How much is enough? The premise is that lowering the flow allows the water to get BOTH hotter and colder.  It stays in the engine longer (getting hotter), then stays in the radiator longer (getting colder).    The limiting factor is the MAX temperature.  It can fluctuate all it wants under the max, but we've got to keep those hotspots below 210F.

But I think an engine with an EWPs is in a unique position to give us the information we need, since it's flowrate can be electrically controlled.  I propose the following experiment (which is easy for me seeing as I don't have a running engine).

-mount thermocouples to measure the water temp going in and coming out of the engine.
-mount a flowmeter inline
-connect a variable voltage source across the EWP
-run the engine up to normal operating temp
-using a rheostats or some type of regulator, start the EWP at 14V and measure the deltaT across the engine after it stabilizes.
-successively drop the voltage in 1/2 or 1/4 V increments, recording the flow, letting the temps stabilize and then recording at each step.

Graphing the results should tell us what flow will give what deltaT.

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This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."