An auto purge for an intravenous contrast injector of the type having a motor which advances a plunger drive ram and configured for use with a pre-filled or user-filled syringe containing an approximate known amount of air including a processor which causes the motor to move and a memory storing a predetermined purge stop point representative of the approximate known amount of air in the syringe, the injector configured to automatically advance the plunger drive ram an amount substantially equal to the predetermined purge stop point representative of the approximate known amount of air contained in the syringe.