IMO, throwing Barr's Leak at a hole in a cooling system is like throwing more toilet paper in the toilet to get it to stop overflowing. It sounds like your cooling system has some serious underlying problems. At a minimum you need a heater core, possibly a radiator. Barr's Leak may sound like a really great thing at first, makes you think that you really won't have to do a cooling system overhaul after all... It's a mirage. A cooling system is way too demanding and important to throw quick fixes at it.