Don't mean to thread jack but, im having the same problem. My coolant is filled to the top, and the overflow tank has plenty in it. Once in a while, ill be driving and the "low coolant" light will come on for a second, then go away. On some days it will stay on for 5-10 minutes, then go away. I don't have a factory radiator, i have an over sized one from zzp. Im not sure what company it is. I know i don't have any leaks anywhere, no milky brown oil, and no oil in the rad.