One thing you gotta be careful about when purging the air from the antifreeze line is low point on the fill hose. On the my YY250T, the fill hose actually dips down below the top of the radiator then arcs back up.
When you go to fill the radiator after the fluid has been drained, you can only fill it up to the top of the lower hose to the pump; once fluid has risen above that level and pushed out the all the air it can from the bleed hose, there is nowhere for the air to escape, and you basically have a 1/8th full radiator, which doesn't effectively dissipate heat. You need to disconnect the fill cap from the frame, bring it outside the frame and raise it up so that there are no low spots in the hose to prevent air from coming back up from the radiator. At that point you can fill it up and put stuff back.
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