Just got back from an 1,800 mile road trip along the Northern CA coast in a 1998 Toyota Camry. With a full upper grill block, and half of the lower blocked, the radiator fan came on only once while climbing a hill in stop and go traffic (I-680, perhaps).
I set my UG to alarm at anything above 210 F, and the fan kicks on at 215 F. I can tell when the fan kicks on because the temps will rapidly fall from 215 down to about 190 degrees.
White coroplast upper block and pipe insulation for half of the lower block