Tensioner & Idler Pulley - Geely & Chana series Tensioner and idler pulleys are essential components in modern automotive engines. They play a critical role in the proper functioning of the engine's belt drive systems, ensuring optimal performance and longevity. They are crucial for the optimal performance of belt-driven accessories such as the alternator, water pump, and air conditioning compressor. By maintaining correct belt tension and alignment, they help in achieving peak operational efficiency. Thay also extend the lifespan of the engine and its accessories because they can prevent undue wear and tear on the belts and associated components.