Used a strange set of channel locks that my father had. Wrapped fabric around the blue cap, snugged up the C.Lock, a little pressure and it began to open. I then slowly continued to open it by hand and stopped when I heard the pressure release. I then continued to open it up an fill with distilled water. Now it is up to the full mark. It has been in the 90s the last couple of days and I wanted to make sure the coolant was at peak efficiency. Thanks again to all who helped with suggestions.
AKL