Radiator sealer stuff is junk. It just clogs up your system, leading to pressure increases in weird places and sometimes it will cause hose tears and whatnot that wouldn't happen otherwise. All that Bar's Stopleak stuff is rubbish, seriously. I tried it on a radiator with a pinhole leak, and it did 0% good - and I tried 5 different brands. Same thing with my friends and their cars. And the radiator shop I called just laughed at me when I told them about this, and said "Another $5 profit for the Bar's company... that stuff is useless."