I was recently asked by a family member to do maintenance on a 2005 Ford Explorer. It has the original coolant in it still so I was going to drain and refill it a couple times. Out of curiosity I used my coolant tester that sucks up fluid and points the needle to a chart. I was surprised to find only clear fluid that appears to be water. Is this ever normal with old coolant to have water at the top? I can't tell if it was only a small layer or if it was all throughout the coolant tank. The car was last run a couple days ago and it only has 23,000 miles on it.