You will be better to use bleed bolt, 10mm, loosen bolt, start bike, remove rad top, it will heat up just let it run, when fan comes on you will notice drop in radiator, full overflow, it will come out bleed bolt when full, just keep adding in radiator, its messy but it works, once its coming out bleed bolt tighten it up and put cap on. You may have to add after a ride and it cools off a little. You will notice overflow leak when bike is cut off and cooled and you know its max full.