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.