When do you have to change oil in 2003 Montana?
When the change oil indicator lights up.
I have an '04 and my lights are different than yours. However, the wavy lines probably indicate level, so you probably have a low oil indicator demanding that you add a quart. My Montana has two oil warnings: a dripping oil can says low oil pressure. A dripping oil can with a wrench below it means I should completely change the oil.