Mine did this everytime we'd go on a run. I attached a hose (5/8 I think is what slips over the square molded outlet) to the overflow bottle and routed it down towards the lower control arm. Problem solved. I think the overflow bottle just burps some fluid out at times, which drips antifreeze on the fan pulley and flings it up onto the hood. I don't seem to lose a ton of antifreeze and I top off during oil changes. It's a relatively inexpensive hack and might be worth it just to see if it fixes it.