A friend of mine is looking to move from his '04 YZ 250F to an '08 YZ 450F and the local dealer let him borrow a used '06 YZ 450F for the weekend so he can see whether or not he would like a 450. Long story short, now that he gotten used to the bike he loves it and cant wait for his '08 450 to arrive, but I have a question. Ive noticed that the bike seems to use coolant. He ran 4 motos today and after 2 motos the bike would be about 1 cup of coolant low. The bike doesnt smoke and I didnt see any leaks, so Im kinda wondering where the coolant is going. The temps were in the 80s today, so its possible the bike was running kind of hot and pushing coolant out of the over flow and its also possible that it has a very slight headgaket leak and its little such a little amount of coolant that there isnt enough white smoke for it to be noticable. So, were these bikes known for using coolant?