Sounds like the pH in the coolant was out of wack. Too high or low and it dissolves metals in the system makes the coolant murky. Electrolysis can set in too and that will strip rust off of the inside of the coolant passages and muddy things up. If you take a multi meter and put one lead to the engine block or other good ground and dip the other lead into the coolant at the radiator cap and start seeing voltage it is over due for a change. The antifreeze part of coolant doesn't really wear out, but the additive packages in them do and that is where the problems start.