 After leaving pro football, Thornhill returned to Pitt as an assistant coach to Warner.In 1922, Warner accepted the head coaching position at Stanford, but as he had two years to finish his contract at Pitt, sent Thornhill and Andrew Kerr ahead to coach Stanford in preparation of his arrival in 1924.Thornhill served as offensive line coach under Warner until 1933, when Warner left Stanford to take the head coaching job at Temple University and Thornhill was named head coach.