In this article, I'll go over the steps involved with replacing the drive belt tensioners on BMW X3 models with an M54 6-cylinder engine. Be sure to work with a cool engine and remove the key from the ignition.
Drive belt tensioners and idler pulley can fail when you least expect it. There are a few warning signs; listen for increasing belt noise, chirping or grinding from the belt area. If you have any of these symptoms, remove your drive belts and inspect the idler and tensioners. Also inspect the main drive belt tensioner for straightness, as the bearing wears and it can tilt, causing your drive belt to fail. 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.
BMW X3 models equipped with an M54 6-cylinder engine utilize 2 multi-rib engine drive belts. A small outer belt drives the A/C compressor and the larger inner belt drives the alternator, coolant pump, and power steering pump. Start by removing both drive belts. See our tech article on drive belt M54 engine, replacing.
Idler: Remove the bolt and the idler pulley together (red arrow) once the bolt has been loosened. If replacing idler, transfer bolt and bushing over to new idler (blue arrows). Reverse steps to install new idler. Once belt is installed, start engine and allow to run for less than 30 seconds, shut engine OFF and recheck belt installation.
Accessory belt tensioner: Using a 16mm socket, relieve tension then remove the pin (red arrow) used to hold tensioner in place when belt is removed. If you did not install a pin when removing belt, skip this step.
Accessory belt tensioner: Remove the tensioner from the engine. Reverse steps to install new tensioner. Once belt is installed, start engine and allow to run for less than 30 seconds, shut engine OFF and recheck belt installation.
A/C belt tensioner: Once removed (red arrow), remove tensioner with bolt from engine (blue arrow). When installing new tensioner, be sure to properly align installation tabs with slots on engine (yellow arrow). Reverse steps to install new tensioner. Once belt is installed, start engine and allow to run for less than 30 seconds, shut engine OFF and recheck belt installation.