Main Drive / Serpentine Belt 7PK1855 - E82 135i, E9X 335i (11287628652)

The main drive belt runs the power steering pump, alternator, and air conditioning compressor on the N54 engine (the water pump is electric). It's very important not to neglect your drive belts as a failure will leave you stranded. The 2006-2010 6-cylinder engines (N51/N52/N54) also have a reputation for "eating belts" - the belt fails and is sucked into the oil pan. A belt is easy to inspect during normal maintenance such as an oil change or refilling your washer tank. If there are cracks running across the ribs, sections missing, the edges are frayed, or the threads are visible on the belt surface, the belt should be replaced immediately. Also pay attention to a belt that is running off the edge of a pulley as that is a sure sign of an impending catastrophic failure.

If you can, inspect and test the pulleys before ordering your belt - tensioner, deflection, A/C, and power steering. Or plan to order new pulleys and tensioner with your belt. These pulleys are made of plastic and shatter with age, causing potentially expansive/expensive damage to your engine, radiator, etc. They usually last longer than the belt but now is the best time to replace them. Since they are bolted on, not pressed, they are easy to replace.

Also test the belt tensioner at the same time as the pulleys. A failing tensioner can let the belt slip off the pulleys. Due to the severity of failure, we recommend replacing the tensioner every 50-60,000 miles. But you might as well do it with every belt change.

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