What year wolverine are we talking? Liquid or oil cooled? I know that my brother had trouble with his kodiak...there is a sensor in the radiator and a sensor in the block that control two different things I think. One tells the fan when to run and one tells the light to come on. Is it spewing coolant out when it overheats? I would start with a downloadable service manual...that will take you through the issue that you are having step by step...good luck...keep posting I am sure that the info is out there!
2011 Yamaha Grizzly 550 FI
2008 Yamaha Big Bear 400 IRS (Sold)
1995 Yamaha Wolverine 350 4x4 (Sold)