Bengtson took his first assistant coaching job at the Missouri in 1935, but soon returned to his alma mater as line coach, staying through the 1939 season. Beginning in 1940, he moved to Stanford, where he served as an assistant coach for twelve years. Bengtson moved to the professional level in 1952 with the nearby San Francisco 49ers. Bengtson resurfaced with the San Diego Chargers and New England Patriots, becoming the interim head coach of the Patriots in late 1972. Later, he was named the team's Director of Pro Scouting, staying through the 1974 season.