Abstract: A belt tensioning system for maintaining consistent and constant tension in a serpentine drive system which includes a series of pulleys and an endless belt interconnecting the pulleys. The tensioning system utilizes a low rate power spring which acts on the idler pulley, and through the idler pulley on the belt, and is suitable to maintain tension over a broad range of belt length variation and pulley locations and provide damping adequate to prevent undue pulley oscillation over a broad range of system vibration conditions. In one form of the invention, the spring itself is effectively fixed at one end to the engine block and at the other end to a tensioner housing so as to operate on the idler pulley and maintain the tension and provide the damping. The hysteresis of the spring, responding to pulley movement, thus assists in the damping.