My 2010 Sportsman 500 HO has been overheating every time we have taken it out this summer. I have cleaned the radiator fins. Just took apart the water pump cover and the water pump is clean and functions when the machine starts up. On the other side I took the thermostat out, checked it in a pan of boiling water and it opens up and operates as normal. The cooling fan is operational (recently replaced). Any other ideas as to why I am having this overheating issue?

Thanks,
Brad