With as open as the bumper is, airflow to the rad isn't effected much at all. If the sides were enclosed and the rad/coolant system wasn't in good working order, you would find out real quick. This is what happened to a buddy after he installed an ARB bumper and winch. After reconditioning his coolant system, the truck w/bumper/winch worked fine.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed