How do modern cars regulate temperature so well?

Add an air dam.

I've noticed my engine will slowly creep up in temp when idling. But if I have any amount of headwind, or just pop the hood release my temps stabilize at the thermostat temp. Hell, if I park somewhere dusty I can actually see air blowing forward from UNDER the car, which I'm sure gets recirculated through the radiator.

One of these days I intend to install an Air dam or even louvered hood vents to see if I can eliminate that.