I went riding the the desert with a friend who's WR450 had gotten pretty hot on a couple of trails and finnaly quit working. When we checked the radiator, after it was cool, it was very low and there was plenty in the overflow. Is the overflow only to catch it when it gets hot? I had a similar experience with my WR426 where the radiator was low, but plenty of coolant in the overflow. I also had this problem with my XR650R, so I am beggining to wonder if the overflow is only to catch the coolant when it gets hot. I thought when it cooled in the radiator it would suck the coolant back but I have not seen this happen.