Their terms are usually for a "rebuildable core" so if you give them a busted block, they cant rebuild it. However, they acquire their cores in two ways: (1) cores customers trade in and (2) buying cores from sources such as wrecking yards and core vendors. It is a certainty that they dont pay $500 to a core vendor for an engine......kinda makes you think that they make a profit on the deal if you dont have a core???? If they take in a busted block, it is near worthless and is sold for the nodular iron (to make stuff like water pipe).

mike in tucson