Have you spoken to Pep Boys about this? If you can prove there was no oil put in then they will most likely cover the cost of repairs. As everyone else has said there may be damage to your engine and that damage may be causing increased friction and the friction causes heat. Low outside temps may mask these effects put they will only get worse. If internal bearing clearances get too high due to wear then the oil wedge which protects journal type bearings will be in effective and something will break.