For what its worth. I like to trail ride my 02 YZ426. In tight sections where slow movement is key. My bike would get hot and dump coolant. (like any other) I did a couple of new things. First I looked at a buddys WR overflow set up then went to the dealer. For $40 and some change I bought an OEM coolant overflow tank that fits the 02 WR. The only issue is the WR has a steel subframe with a forward tab welded for the tank. Where my Yz has an aluminum sub frame and no tab. I still need to find some one who can tig weld a tab on the sub frame. With a dremel I had to cut out some plastic, route some hose, and make a clamp for the aluminum sub frame. I marked the cold coolant level with a pen and took her for a spin. In this hot weather it didnt take long to get her hot. Sure enough we had additional coolant in the overflow tank. Once I started riding a regular pace and cooling began there was enough vacuum to open the rad cap and suck that coolant back into the tank. So far its working, looks clean and clears the tire just fine. If you run your bike hot this should help.