When my son bought his first project a `68 dart it had a 273 in it, right away he decided to install a built 360, we knew the rad had leaked when he bought it, no big deal but we decided to back flush everything before he put in motor and rad, opened the petcock and it just oozed out for the first entire day even when water was added it just oozed out, took three days to flush til clear water flowed with prestone back flush. I`m just not a fan of using the stuff myself...