The BMW 525i comes equipped with a V8 engine mounted longitudinally to the frame. On the front of the engine is a long, 3/4-inch-wide belt wrapped around several pulleys that drive the various accessories attached to the engine. This is the serpentine belt, so named for it's circuitous route around the front of the engine. The procedure to remove the serpentine belt is not a complicated one, only requiring a few common tools and minimal skills.
The BMW 525i serpentine belt is made of reinforced rubber/neoprene and has tremendous stress placed on it when the motor is running. The aforementioned materials will age with use, and heat or cold will affect the belt's durability. BMW recommends replacing the serpentine belt every four years or 60,000 miles. Fortunately, replacement belts are available at all auto supply dealers, and they are relatively inexpensive. Removing the installed belt is the first step to installing a new belt.
Also, you will have to remove the serpentine belt to service the accessories powered by the belt's rotation: alternator, water pump, oil pump, power steering and braking. The first step to any maintenance on these components begins with removing the serpentine belt from the drive pulleys.
The BMW 525i's serpentine belt is not difficult to locate if you look down in the engine bay at the front of the motor. Depending on the year and model of your BMW 525i, there may be a cover placed over the space between the forward radiator and the engine block. If such a cover is in place, you'll have to remove it for access to the belt.
Removing the BMW 525i's serpentine belt begins by locating the tension pulley; you will find it about mid-way between the top and bottom of the motor. This pulley is not attached to an accessory or to the drive train. It's is a spring-loaded pulley that keeps the belt tight, but it can be manually pushed to one side to release the serpentine belt.
The tension pulley on the BMW 525i has a cap on it to secure the pulley's interior. Remove the cap by inserting a screwdriver underneath, and it will pop off. In the center of the tension pulley is an 8-millimeter Allen socket. Take an Allen wrench adapter on a socket wrench and insert it into the pulley, then pull up. You will encounter some resistance, as the spring holding the tension pulley is very strong. When turn the pulley, it will slide to the right (as you look at the engine). Once the tension on the belt is relieved, you can slip it off the pulley. The socket wrench will be in the way, but just allow the belt to rest on the socket. When you remove the socket wrench, the belt will easily come out of its route around the engine.
