I remember when I used to race desert a lot, some of the people who went to flag the course that rode KX500's would run into heating problems. Temperatures reaching over 110 degrees, a big barrel to cool, and the lack of airflow through the radiator would plague some of these bikes. I know one thing that helped a lot was to run a lot more distilled water in the radiator than coolant (like a 70/30 ratio). Coolant has great anti corrosive properties and a high boiling point, but water actually does a better job of cooling the engine. I found this out when I blew a radiator hose in the desert on my van, and when I put pure water in the radiator, it ran a lot cooler. In conjunction with running a greater amount of water than coolant, it's also wise to run a higher pressure cap, as the higher the pressure, the higher the boiling point. I think Kawasaki lists various radiator caps for the K5.
