Replacing the Aux Fan Increased Noise Vibration Harshness

[m3f_abcurran]

So, my original aux fan motor died earlier this week. I found a used e36 aux fan, motor, and shroud, and did the repair yesterday.


The donor aux fan assembly was not OE. Thus, the shroud, motor, and fan all had slight differences from the OE parts. Those differences are:

• The OE shroud has a slightly different opening at the top right, which I decided should stay in the event it directs airflow to somewhere in the engine bay. The donor fan has three protrusions (you can see in the pic below.)

• The donor motor has flats machined onto the shaft, and the donor fan fits onto those flats and is secured thereto with a nut. The OE fan fits the circular OE motor shaft and is secured with a circlip.

While the OE fan would and did fit the donor motor, I decided to use the donor fan to avoid a situation where the nut might loosen and the fan would not spin at speed with the motor.


So, I swapped the donor motor and fan to the OE shroud. I torqued the nut as best I could considering there's no way to hold the motor shaft while tightening.


Here's where I screwed up: Before reassembly, I removed about 4-5 rusted body nut clips from the donor fan blades. (Again, in the pic below, you can see the clips on the fan blades.)


I also removed from the fan shroud and the AC condenser any weather stripping that was disintegrating. I used compressed air blown into the AC condenser to remove any accumulated dirt/debris.


The initial test drive following installation was fine. The Aux fan came on when I turned the AC on, and the AC blew cold. I drove about 7-8 miles in local city traffic and there were a few sustained runs around 40-60 MPH. I did not experience any increase in noise, vibration, or harshness ("NVH"). The AC was on during the test drive.


But, a few hours later, there was a significant increase in NVH immediately upon start up when the AC turned on. Vibrations are felt in the cabin through the seat, and door panels audibly rattle. Increased noise comes from engine.


The vibrations subside when the AC is turned off. However, to isolate the problem, I turned the AC off but could still feel some smaller vibration when the radiator fan turned on. (The car does not have the mechanical fan. Rather, it has a 16" Spal puller on the back of Zionsville radiator.)


I'm really at a loss here, because everything was fine after it was installed. Obviously, the starting point is to replace the body nuts on the Aux fan blades.


Is there a method to properly balance the fan?


Could the partially removed weather stripping cause a disruption in air flow such that it would be felt in the cabin?


Could the compressed air cleaning have damaged a blade on Spal fan, even though it had to travel through the condenser and the radiator before hitting the fan?


Should I just go back to the OE fan, even though it's not designed to fit the flats on the donor motor?


Is this a dying AC compressor?

[m3f_Aeko]

Are you certain the aux fan is the cause of the vibrations? I seriously doubt it could cause a powerful enough vibration to shake the door panels because it just doesn't have that much mass to it. Vibration like that is on par with driveshaft imbalance, however as you said it's tied in with the AC turning on. I have had aux fans that were cracked enough to move freely and contact the shroud but didn't vibrate nearly that bad.


I'd try disconnecting the aux fan and turning the AC on momentarily to completely verify whether or not it is the cause of the vibrations.

[m3f_abcurran]

No, not certain it's the Aux fan, but since this was the part that was changed, that's the focus. It doesn't shake the door panels, rather the vibration just causes some of the clips in the door panels to make a sound.


It's not the drive shaft. This vibration happens while stopped and corresponds to when the AC is turned on or off, or when the condenser kicks on/off.


It could be AC condenser? I guess I could pull the fan fuses and turn AC on and see what happens, or jump the pins on the fan switch to power the aux fan to get them running independently.


It could be the Spal puller fan, but that doesn't seem likely.

[m3f_pbonsalb]

The body nut clips are for balancing the blade. Can you see scratches or discoloration from where they were and reinstall them?

[m3f_Aeko]

No, not certain it's the Aux fan, but since this was the part that was changed, that's the focus. It doesn't shake the door panels, rather the vibration just causes some of the clips in the door panels to make a sound.



It's not the drive shaft. This vibration happens while stopped and corresponds to when the AC is turned on or off, or when the condenser kicks on/off.

That's fair. I was using the driveshaft as a comparison. I'd definitely try pulling the aux fan fuse and see if that immediately kills the vibration.

[m3f_Braymond141]

Is there a reason you didn't just get a new one? The OEM version is $152 with a liftetime warranty. It's the same exact part.


https://www.fcpeuro.com/products/bmw...em-64508364093





They are balanced. Note the weights on the blades.

[m3f_abcurran]

Is there a reason you didn't just get a new one? The OEM version is $152 with a liftetime warranty. It's the same exact part.



They are balanced. Note the weights on the blades.

Thanks, for the picture, Brett. Admittedly, I didn't look too carefully at Turner's photo once I realized they were charging $40+ more than FCP and it wouldn't ship for 5 days.



I didn't buy new because time is of the essence. It's been in the mid 90s with nearly 100% humidity in the NYC area for the last week. We need a functional AC without risk of overheating.



Motor failed Sunday night, but I wasn't able to figure that out until Monday night. I was able to get the used part Tuesday and install it Wednesday.



With the holiday in the middle of the week, if ordered Tuesday, the new VDO fan from FCP wouldn't have shipped until Thursday. Even though I've gotten some shipments from FCP two days after ordering, I'm not sure this would have arrived Saturday.

[m3f_abcurran]

Just to bring some resolution to this in the hopes it might benefit someone down the line...


I tried to balance the donor fan blade. I wanted to use a wooden dowel pushed through the fan center, then lay the dowel perpendicularly across two, parallel, level, straight edges. At that point, I'd let the fan roll until the weight was at 6 o'clock, and start attaching the weights to the portion of the fan blade closest to 12 o'clock until the fan stopped rolling at random positions. Similar to this picture.





But because the donor fan was made to fit the flats on the motor spindle, the fan would tilt on the dowel. That's what you get when you fit a round peg into an oval hole.


I'd already bought some "speed nuts," which is apparently Home Depot speak for a body clips - those little metal clips through which a bolt can attach two plastic pieces. I was able to see where the original weights were before I stupidly removed them, and put the clips back on in the same locations.


Started up the car, turned on the AC and the vibration was gone.


I could have used some threaded rod, washers and nuts, but didn't have anything in size handy and wasn't going back to the store. Maybe I'll do that some day, but I'm calling this job done for now.