I got an 01 yz426 and recently I changed my coolant out with engine ice coolant and it ran great when it was first put in. But now I've put around 15 or less hours on it since i replaced it. Now about every time i ride it it seems to be low on coolant so i fill it but then it seems like it overheats and it comes out the overflow. I talked to my local yamaha dealer and he said something bout a sensor on the radiator. i looked briefly but didn't see anything. but he also said its very unlikely that it would be the water fan. I don't know if i need to replace the coolant again or if it just has too much coolant in it or what.... If any ones had a similar problem let me know what u did bout it and how to fix it.... I also do a lot of woods riding and was at a friends doing slower riding when i first noticed it. but it was a colder night a couple weeks ago in an open field when I rode and it still did it.