Someone? 250 radiator on what?  An lt500, 250,450...
Is it a drag atv, mx racer, duner?  how long is it ridden at high rpms. If its a drag racing atv that doesn't represent desert riding bc it involves sustained high speed riding with ambient temps that exceed 37C. Drags last a few minutes total with a warm up, stage, run, get back to the pits and shut off/cool.