How do you loosen a serpentine belt on 02 BMW e39 530i?

Answer 1

One of the five pulleys in the alternator/Power Steering/cooling system group is a tensioner. It's on the right side (driver's side) and it's the middle one (it's also smaller than the others). Pry off the dust cap with a flat head screw driver and there will be a spot to insert a T-47 torx (though a T-50 will also work and is easier to find). Turn this counter-clockwise to loosen the tension and the belt should slip off. If you're going to be removing the belt and putting a new one on (recommended, obviously), then you're going to need to remove the fan clutch and fan shroud. Do this step before loosening the tensioner if you're going to replace the belt! It's a somewhat involved DIY, but certainly not hard and well worth it. Your toughest part will be taking the fan clutch off then putting it back on. They sell a tool to facilitate getting it off, or you can just use the belt's tension to keep the water pump pulley in place as you hammer a 32mm wrench CLOCKWISE to get it off (it's reverse threaded).