Dex-cool is acidic. If air enters the system(low coolant levels) rust deposits will form in these pockets in a short time. Thats why it gets rusty looking. Manufacture recomends replacing every two years.
Just about every vehicle that comes into the shop with 5 or more years on it usually have the rusty looking coolant jug. However the newer pink stuff is less acidic.
It seems the multi-purp aftermarket coolants are a better way to go.
dex-cool is junk. Flush it out!
