Hello, whenever I drive my 2002 Polaris Sportsman ATV, the fan will come on in about 5 minutes, then the high temp light will come on in about 15 or 20 minutes. I live in Maine, so its around 20F right now. It started doing it back in the summer, so I washed out the radiator with a power washer. But it didn't change a thing. I think it might be that the thermostat stuck closed. I was going to replace it, but I don't have a clue where it might be.

 

Follow hose on left side to engine,remove plate,thermostat behind it. Could also be air pocket in radiator,can cause this,or even temp sensor at bottom of radiator starting to go if fan is erratic??