The serpentine belt on the front of the BMW N52 engine is responsible for driving the power steering pump, alternator, and A/C compressor. If either the belt or the tensioner fails, you'll lose your power steering, and the battery won't be receiving a charge. It's recommended that the belt be changed every 80,000-miles, and that the belt tensioner and idler pulley should get replaced along with it. If either of the bearings in the pulleys seizes, the belt can snap and get sucked into the engine.
Changing the belt drive system is great "while you're in there" maintenance as a lot of the removal and reinstallation process happens while doing any other repairs or replacements on the front of the engine. This is an easy job that'll give you that extra bit of peace of mind, and unlike BMW's more complicated jobs, replacing the belt, tensioner, and pulley only requires the use of sockets and ratchets. Be sure to follow along with Gareth in the video below for visual guidance.
BMW models and years applicable:
How much will it cost to replace the serpentine belt system on a BMW N52 engine?
The BMW N52 Drive Belt Kit that we sell on our website comes with every part you'll need to complete this job for just under $80. While the parts won't have BMW's stamp on them, they come from the same company that supplies BMW with their parts.
How long will it take to replace the serpentine belt system on a BMW N52 engine?
BMW's longitudinal engine layout places the belts at the front and center of the engine bay. To get to them, you'll remove the fan assembly and the intake airbox. Once you can access the drive belt system, you'll only need to remove two bolts to remove the parts that you're replacing. Altogether, you can finish this job in under an hour without any issues.
Parts required to replace the serpentine belt system on a BMW N52 engine:
Tools required to replace the serpentine belt system on a BMW N52 engine:
- E14 Socket
- T20 BIt Socket
- T25 Bit Socket
- T60 Bit Socket
- 10mm Socket
- 16mm Socket
- Ratchet Extensions
- Torque Wrench
- Flathead Screwdriver
Steps required to replace the serpentine belt system on a BMW N52 engine:
Step 1: Remove the airbox
Open the hood and remove the two mounting fasteners for the intake snorkel.
Then, pull the snorkel off of the airbox and out of the engine bay. Next, use a 10mm socket to remove the two airbox mounting bolts.
Reach behind the airbox with a flathead screwdriver and loosen the hose clamp that holds the intake tube to the airbox. Then, disconnect the mass airflow sensor.
With all of that disconnected, pull the airbox up and out of the engine bay.
Step 2: Remove the fan assembly
First, unplug the electrical connection that runs across the top of the fan housing. If you're struggling to undo the connection, use a flathead screwdriver to help push in the tabs and separate the connection.
Next, pull the expansion tank line out of its clips and off of the top of the fan shroud. At the top of the passenger's side of the shroud is a fastener securing the shroud to the radiator support. Remove the fastener with a T25 bit socket.
Below the fastener, there may be a wire zip-tied to the fan shroud. Clip the zip-tie if that's the case.
If your car is equipped with an automatic transmission, it'll have an external oil cooler attached to the fan shroud. Use a T25 socket to remove the single fastener mounting the transmission oil cooler to the fan shroud.
Now, with everything removed from the shroud, pull the fan assembly out of the engine bay. The assembly is a tight fit in the space it occupies, making for a tricky removal process. Go slow when pulling the assembly out; wiggle and twist the shroud to get the various tabs and lips clear of the stuff around it.
Step 3: Remove the accessory drive belt system
Before removing anything, take note of how the belt is routed. Then, use a flathead screwdriver to remove the covers from the idler pulley.
Next, insert the T60 socket into the tensioner and rotate and hold it to the right. Doing this will release the tension from the belt so you can pull it off the front of the engine.
Use a 16mm socket to remove the idler pulley that bolts to the alternator. Then, use an E14 socket to remove the tensioner's only mounting bolt.
Step 4: Install the new accessory drive belt system
Take the new idler pulley and thread it into the alternator by hand to prevent cross-threading to the bolt. Then, fit the new tensioner into position on the front of the engine and thread in its mounting bolt.
Use a 16mm socket and a torque wrench to tighten the idler pulley bolt to 40Nm. After that, use the E14 socket to torque the tensioner's bolt to 25Nm. Then, because the tensioner's bolt is aluminum, tighten the bolt another 90°.
Before throwing the belt on, reinstall the caps to the idler pulley. Then, route the belt onto the front of the engine. Ensure that all of the belt's ribs are seated correctly in all of the pulleys' grooves. The belt can come off or shred itself if it isn't seated correctly.
If you rout the belt correctly, there will be just enough room for it to fit correctly. When you are certain that the belt is routed and seated correctly, pull the pin from the tensioner to tension the belt.
Step 5: Refit the fan assembly
Carefully slide the fan shroud and assembly down into the engine bay. Then reinstall the shrouds mounting fastener.
Use a T25 bit socket to tighten the fastener; then, if your vehicle has an automatic transmission, head under the car and reattach the transmission oil cooler to the shroud. Use a T25 bit socket to tighten the transmission oil cooler's fastener.
Next, reconnect the electrical connection that runs across the top of the fan shroud and refit the expansion tank hose into its clips. Lastly, resecure the wiring below the shroud's fastener to the fan shroud with a new zip-tie.
Step 6: Refit the intake airbox
Take the airbox and fit it into position in the engine bay. Ensure that the airbox fits into the rubber isolator on the chassis. Then, refit the intake tube to the airbox and secure it by tightening down its hose clamp with a flathead screwdriver.
Next, reconnect the mass airflow sensor and thread in the airbox's two mounting bolts. Use a 10mm socket to tighten the bolts.
Lastly, refit the intake snorkel to the airbox. Secure the snorkel to the radiator support with its two fasteners, and tighten them.
BMW N52 serpentine belt system torque specs:
- BMW Idler Pulley Bolt = 40Nm or 29.5 ft-lbs, of torque
- BMW Belt Tensioner Bolt = 25Nm or 18.4 ft-lbs, of torque plus 90°
And there you have it; a complete guide to a drive belt system change on your BMW's N52 engine! If you're interested in more DIYs for your BMW, you can visit bmw.fcpeuro.com and subscribe to our YouTube channel.