This situation needs to be brought to the attention of all late model BMW owners. This would include all vehicles produced after 1992. BMW has opted to use plastic water pump, power steering, tensioner, and idler pulleys. Although this may be a good choice for weight reduction and reduced manufacturing cost, it is not a good choice for durability and longevity. We have had several vehicles in our shop where the pulley has cracked, resulting in a broken serpentine belt, and an expensive tow truck ride. Although the serpentine belts have far superior wear and traction characteristics, these items are not to be forgotten when performing your service inspection.

Serpentine belts are internally fiber reinforced. Remember these belts operate with a self-adjusting belt tensioner. The squealing belt warning that you may have experienced on an older generation vehicle indicating a loose or worn "V" belt does not occur on vehicles with a serpentine belt. Although serpentine belts last longer, they will break with little warning!

Idler and tensioner pulleys: These pieces consist of a simple sealed ball bearing pressed into a plastic outer wheel. Due to the small 3-inch diameter these units spin at twice the RPM of the engine, for example at only 4000 engine RPM the tensioner is spinning at 8000 RPM. Needless to say replacing these items is cheap insurance against catastrophic failure.

Here is what to look for:

1. Make sure there are no external cracks in the rubber.
2. Any shreds of fiber cloth material exposed at the edges are indications of needing replacement.
3. Inspect the traction ribs that interlock with the pulley grooves. Any indication of cracks across the rubber requires replacement.
4. Look at the back of the belt (the smooth side) this side rides on a smooth tensioner pulley. If this side is highly polished and appears dry, the belt is most likely very old.
5. Replace all belts every 30,000 miles or sooner if wear indicates.
6. Replace plastic pulleys and tensioners at the same time.