Champion Radiator and Factory Shroud

Leave open for better cooling air at speed, unless you have heating issues stopped at idle; there is a (very slight) possibility of air being drawn back from the engine compartment through these gaps to the front and through the rad again, which could effect idle cooling. If idle cooling problems arise, then you may try blocking the gaps and see if it helps (amongst other things). If it helps at idle, then retest at high cruise speed and see if the high speed cooling has been hurt by the blocked gaps.