Hi everyone, I’m new here. I’m on e46Fanatics sometimes when I need to keep the Ultimate Fixing Machine running. Thanks for all the good technical info, this may be helpful to someone since I couldn’t find a lot of detailed DIYs for the X53 3.0 alternator.

The battery light came on while driving home, tested the voltage under the hood while the engine was running and it showed 10.5V, turned the car off and it showed 11.3V (no need to do this from the battery BTW) I decided to just replace the alternator and not mess with trying to figure out if it was the voltage regulator (which you can buy separately)

On a scale of 1-10, I’d say this is a 3 for the average DIY gearhead, it wasn’t that difficult since the alternator is right on top. Removing the radiator cooling fan without the “tool” was by far the hardest part of the job.

The last alternator I swapped out was from my old Eclipse years ago at 160K miles so 50K miles is really premature. Dealer quoted $509 for what really is about a $200 alternator, there is nothing special about it that makes this alternator worth $509 except for the BMW sticker. So, f*ck OEM which only lasted 50K miles. I later found out why it failed, more on that later.

Shopped around and found the OEM Bosch 120amp alternator on Pelican Parts for $219.75. Sourced one locally for even less than that (plus the refundable core charge) it did come with the pulley. Best of all, it was made in the USA with a lifetime warranty. Again, f*ck oem.


Tools needed:

Metric sockets 10mm-17mm
Breaker bar (not necessary but sure does help a lot)
32mm long wrench (or large crescent) wrench for the radiator cooling fan
BMW Fan Tool (a long screwdriver and some cussing also works)
T-50 Torx
5/8 socket
Pry bar
Piece of cardboard to protect your radiator (USPS Flat Rate box works great)
WD-40
Shop towels
Latex gloves

Parts needed:

Alternator (120amp) ~$200
Serpentine Belt $18 at PelicanParts.com
A/C belt $8 at PelicanParts.com




First, disconnect battery leads in the back of the vehicle (under the spare tire in case you have not been back there) You’ll have to remove the triangle metal brace under the turtle-looking metal thing. Trickle charge your battery if voltage is really low or replace it if it’s close to dying. A dead battery can kill your new alternator. My local Batteries Plus quoted me $129 for an identical replacement battery (East Penn 94-LI with a $10 MIR)

Remove the large plastic intake duct, there are 4 pop-rivets that hold it in place. Pull the middle pins out carefully so you can reuse them. Don’t drop them in the engine compartment or they are lost forever.

Unclip the MAF from the airbox and remove the two 10mm bolts holding the airbox and remove. This is a good time to change your air filter. ($12.75 for the oem Mann filter from Pelican)



Remove the 3 pop rivets holding the radiator fan shroud.



Unplug the electrical connector from the left side of the fan shroud and unclip the harness



Remove the radiator fan, I used a large crescent wrench and a screwdriver. A little WD-40 may help loosen it but put a rag underneath so you don’t spray the pulleys.
***Note: the fan clutch nut is left-hand thread so you need to turn it clockwise to loosen. It’s easiest to remove the fan and shroud together. Set aside and store the fan vertically as it sits in the engine bay.

Finally, you can actually see everything. Tape the piece of cardboard to the inside of the radiator to protect it from tools, etc. Remove the upper tensioner via the 2 bolts holding it. Some people remove the Power Steering fluid reservoir above the alternator and pull out the alternator that route but I didn’t want to risk it leaking on the new alternator so I did it this way, you decide. (stupid location for the PS reservoir IMO)



Remove the nut securing the main red + cable lead to the alternator with a 17mm socket. Unplug the harness plug from the back of the alternator. You can now remove the upper and lower bolts holding the alternator. I had to use a pry bar and then my gloved hands to wiggle the alternator out, it’s on there pretty tight. Be careful not to damage the plastic “snorkel” since you need to return the core in good shape, it just comes off with a lot of wiggling.









I removed the alternator pulley side up, straight up and out of the engine bay via the front of the engine (the cardboard kept my radiator unscathed so use it) After close examination, I found out why the alternator failed so prematurely (see pic)





Now, compare your new alternator with the POS oem one. Make sure they are exactly the same, correct amount of grooves in the pulley, same mounting points, plugs, etc. I re-used my oem nut for the main red power lead since it had insulating plastic on the outside with the metal part inside.

Installation is the reverse of removal. Remember to reinstall the tensioner. Also, the upper non-tensioner wheel (which is also the connected to the long bolt holding the alternator) is slotted for proper alignment.

Now is the time to install new belts (new pulleys, new thermostat, and new water pump if you’re so inclined, this way you don’t splash coolant all over your new belts)

Pop off the cap on the lower tensioner and use the breaker bar and the Torx T-50 to relieve tension by gently turning clockwise. The T-50 bit is really easy to snap off so be careful. Remove both belts and install the serpentine belt first.



Use the breaker bar and the 5/8 socket to relieve tension on the upper tensioner by turning clockwise. Install the serpentine belt first, then the A/C belt. For the serpentine belt, I found it easiest to loop everything around and to leave the alternator last. Make sure the belts are seated in the grooves properly or else the belts can shred or worse, come off and damage something.

Install all the remaining parts in reverse order. Make sure everything is plugged in and tightened up and all no tools are left under the hood (I forgot to plug in the wiring harness on the side of the fan shroud) Turn on the ignition but don’t start it, let everything re-set for a minute. Start it up and let it idle for a few minutes to make sure everything is okay. Check the voltage while the engine is running, mine showed around 14.5V. Now is the time to go for a test drive.

I still had some random dash lights stay on but everything went away after about 10 minutes of driving. Best of all, the battery light is OFF.