This does happen with 500E's, part of the design trade off of stuffing a V8 into the space where only a I-6 was designed to go.
fad is right on with his assessment, Redline brand "Water Wetter" is a additive that when added can reduce the temps somewhat, say 5-10 degrees? The pigtail modification will allow your aux cooling fan to kick in at lower than standard temps, preventing the car from ever reaching 100 degrees.
This issue is brought up usually during Spring and early Summer but thanks to you, we can all do a little preventative maintenance and get our Cooling Systems in shape before our worries start.
BTW, don't you just love the Border???