when you filled it up, did you leave the little hose off the head untill antifreeze came out? if you have an air pocket, that could stop the coolant flow through the cylinders but still see coolant moving in the radiator. now that you remove the cap and filled it back up, you my have gotten all the air out. take it for another ride and see. other wise check for blocked rad,bad impleller, or improper jetting.