I currently have a 2008 KX450F and this is the second summer I have owned it. The first summer I owned it, I did different types of riding track and hillclimbs with no wind and 90+ degree days. Now this summer it has started overheating I have heard it boiling about three times and it has overflowed almost everytime i have ridden in the past month. First i checked the pump to make sure it still works and it still spins when i pull the kick starter. Then I checked the oil to see if any coolant had gotten into it and it was clean. Then I removed the radiators and hoses to check for any blockage and there wasnt any. Plus ive been running Engine Ice and its still boiling that, but nothing happened last summer doing the same type of riding.