problem with radweld is it doesnt just stay in the rad. It gets flushed around all the water ways including the engine. I think you made a mistake using it personally as ive seen the mess it makes to the engine block and water paths once radweld has been used. On a celica i worked on where the rad was filled with radweld, i did the head gasket and noticed it blew the head gasket as a RESULT of using radweld. This was because all the water ways on the bottom block and clogged up with said radweld and stopped the water flowing through the engine, in turn warping the head and blowing.