If you can find the old plug make a groove across the top of it wide enough to nest a plastic tiewrap, then insert the plug back into the radiator grommet and tie-wrap it to the radiator (thru the core and around the frame and over the groove you made on the plug) to keep it from blowing out again. If you can't find the old plug you will either have to buy one somewhere or go to a pick&pull and get a temp sensor or plug to cap the hole.