This tension roller maintains the correct tension on the accessory drive belt that powers the engine-mounted alternator, water pump, and fan drive. It is mounted on a bracket bolted to the engine block, where it presses against the belt's slack side to prevent slip and ensure consistent pulley speed. A worn bearing in the roller produces a chirping or squealing noise at idle, and the belt may begin to flutter or shed rubber. The roller's outer diameter matches the original pulley path, so the belt rides at the correct height relative to the adjacent pulleys. On replacement, inspect the belt for glazing or cracking and replace it if worn.