Tried all coolant types to help reduce overheating when riding tight trails with my 99 YZ400F. Last year I followed a suggestion from someone here, and bought the WR overflow bottle from MRCycles for less than $15. I have not had to add any fluid since I did that last summer. Sure, it gets hot sometimes and the overflow fills a bit, but running fluid to the bottle and back cools it a lot. Not losing fluid is the main thing. As you lose fluid over the couse of a ride, it has less and less to cool with. I highly recommend this easy mod. Just make sure you mount it on the outside of the frame, and grind the side cover a bit. Inside the frame, and the tire rubs on it.