I never did, nor would recommend using a small server fan in front of, or behind an automotive radiator.Way too weak to yield a meaningful effect. Look for a Spal of at least 12",
better 15" diameter which will deliver ten to fifteen times the air volume
and also survive rain. As always use the proper gear for the application.
My applications for these fans falls strictly into 'other', and I almost always use the largest diameter fan I can squeeze into the application, and speed control via voltage from minimum whisper quiet, to screaming banshee intolerable for long noise levels.
I linked the 254 cfm fan only as an example of a powerful 'computer' fan, considering its 120mm diameter size and 38mm width.
I brought up these fans only to share my considerable amount of experience regarding experimenting with various fan designs. The variables being blade/impeller design, fan rpm, amp draw, distance from restriction, and efficacy when pulling vs pushing configurations, all of which are valid points in the consideration of adding additional fans, all of which that were apparently lost on you, making any further attempts at enlightenment, both pointless and futile.