BMW fitted both mechanical and hydraulic belt tensioners to their models, and the only way to know which one has been fitted to your BMW is with a visual inspection. The belt tensioner keeps the main drive belt tight, ensuring there is enough traction for the water pump and alternator to work. Something as simple as a loose belt can cause a failure of both the cooling and electrical systems. This part has been manufactured by BMW's original equipment supplier INA.

Please note although they are visually identical, this tensioner will not work as a replacement for the air conditioning belt tensioner. The pulleys for the mechanical tensioner are not offered individually.