I recently noticed the engine coolant in my 2000 Grand Cherokee is brown and
dirty looking. Using a hydrometer, the fluid tested fine for temperatures, and
the engine doesn't overheat. I was thinking maybe just a rad flush would do the
trick. I haven't had one done yet. I was reading that sometimes more than one
flush may be required to clean it out fully. Any advice on possible causes that
would turn the fluid brown?