I used it, and will again next spring, I would think it is taking it's time to clean as each day it heats up to temp it just removes more age from sitting.
Anti Freeze is a lubricant also and it will eventually be clean again one day as you flush it, it will take time to lossen everything up. Test for freeze point and run it or change it again. been there my self on my Ramcharger flushed when I put a used 318 in it and all was good , know it has a brown tint to it.