Two drive belts in the M54 6-cylinder engine drive the accessories pulleys at the front of the engine. Power steering pump, coolant pump and alternator are driven by one belt and the AC compressor is driven by a separate belt. Each belt is tensioned by a tensioner pulley.
Note that the engine cooling fan is electric and not belt-driven.
The belts are tensioned by strong tensioners and do not need periodic adjustment. But they will, over time and due to heat, cold and the rigors of operating multiple pulleys, develop signs of wear: cracks, fraying, glazing or missing chunks. In addition, the tensioners and idler pulleys may develop defects. Bearings in these pulleys are life-time lubricated. The lubrication eventually dries up or wears out and may cause noises. If a pulley bearing deteriorates, it can tilt and allow the belt to fly off the pulleys. If it seizes it can damage the belt quite quickly due to excessive friction.
With your engine cold and turned OFF, inspect your drive belts for wear. The belts should be free from cracks, fraying, glazing and missing chunks. Replace belts if any of the previously mentioned issues are present or every four years. In this article, I'll go over the steps involved with replacing the drive belts on the M54 6-cylinder engine. Be sure to work with a cool engine and remove the key from the ignition.
Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.
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On X3 models, the belts can be serviced from below. However, this requires engine splash shield removal along with moving oil and power steering hoses out of the way. It is much easier to remove the engine cooling fan, then replace the belt from above. This tech article will highlight that method.
BMW X3 models equipped with an M54 6-cylinder engine utilize two multi-ribbed engine drive belts. A small outer belt drives the AC compressor and the larger inner belt drives the alternator, coolant pump, and power steering pump.
Start by removing the four T25 Torx fasteners (red arrows) for the fresh air intake duct. Next you will unclip the five air filter housing retaining clips. Lift them up and unhook from the lid of the intake air housing. Start with the two near the mass air flow sensor. Then release the front clips.
This photo shows both drive belts from above. The AC belt is indicated by a yellow arrow. The accessory (main) drive belt is indicated with a red arrow. I will be working mainly from above the engine. Before removing the drive belts, mark the direction of rotation (if reusing belts) and note the installation position.
Locate the AC drive belt tensioner (green arrow). Using a T55PLUS (green arrow) or T60 Torx, rotate the AC belt tensioner (red arrow) clockwise to release tension and slide the belt off the pulleys. When tension is relieved, place a 7/32 pin or drill bit (yellow arrow) in the small hole above Torx slot to hold tensioner in position for belt removal.
Using a T55PLUS or T60 Torx, rotate the AC belt tensioner clockwise (red arrow) to release tension and slide the belt off the pulleys. When tension is relieved, place a pin (yellow arrow) in the small hole above Torx slot to hold tensioner in position for belt removal.
Locate the accessory (main) drive belt tensioner, then locate the 16mm HEX boss (yellow arrow). Using a ratchet with a long handle and a 16mm socket (green arrow), rotate the drive belt tensioner clockwise to release the tension. When tension is relieved, place a 7/32 pin or drill bit in the small hole (red arrow) above HEX boss to hold tensioner in position for belt removal.
Slide the belt off the pulley and remove. With the belts removed, inspect the pulleys for lateral play or binding. The idler pulley commonly fails. If this occurs the coolant pump will lose the drive belt and the engine will overheat. Now is a good time to replace the idler pulley to prevent future problems. See our tech article on Idler Pulley Replacement. To install the accessory drive belt, begin by wrapping the belt around the crankshaft pulley, then over and around the power steering pulley, around the alternator, around the coolant pump, around the tensioner pulley and slide the belt onto the idler pulley. Once the belt is properly installed on all accessories, release the tensioner and remove the 7/32 pin (as described earlier). Tension the belt and check that it is properly aligned and installed in all pulley grooves correctly. Be careful not to force belt onto the pulleys, as damage may occur. To install the AC drive belt, begin by wrapping the belt around the crankshaft pulley, then onto the AC pulley. Next bring a loop of the belt toward the tensioner and over the pulley. Once the belt is properly installed on all accessories, release the tensioner and remove the 7/32 pin (as described earlier). Release the tensioner and check that the belt is properly aligned and installed in all pulley grooves correctly. Be careful not to force the belt onto the pulleys, as damage may occur. Reinstall intake air duct. Start the engine and allow it to run for less than 30 seconds. Shut the engine OFF and recheck the belt installation.