How do modern cars regulate temperature so well?

kursplat said

THE AUTO COOL GUY's web site is bad...he really needs someone to redo it and rewrite everything. his PWM controllers are interesting if that's the style of controller you want. HERE'S the instruction pages. setting the "ON" temp basically involves using a heat gun and setting the on temp, measured at the radiator outlet, ~ 10' below what your thermostat opening temp is. that sets the "ON" temp, and the controller ramps the fan speed up and down using that for a base line

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That seems like a terrible way to do it. So it's just a variable controller. Except electric fans aren't generally rated for variable speeds, they're rated at one speed. And the fan itself will be designed to be most efficient at that rated speed. That also means the fans are always on at some speed once you're within 10° of the thermostat open temperature? Again, there's no reason for that. The fans don't need to run at all once the car is moving at a reasonable speed, and the temperature won't necessarily drop low enough to shut them off even though you don't need them to be running.

Not only that, but most electric motors tend to like a specific RPM range. Not all fans may like being hooked to a variable controller like that. Big pass on that one.