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Tuesday, April 23, 2024

Doug's Domain

Doug Vetter, ATP/CFI

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Saturday, May 23, 2015

Aux Fan Failure and Replacement

(Image: BMW Special Tool used to remove windshield adhesive)During a brief spell of hotter weather last week I found myself using the air conditioning for the first time. I hadn't noticed any issues while driving the first leg of my trip but when I got in the car for the return trip I started the engine, turned on the air conditioning, and immediately noticed the backlighting in the gauge cluster dimming once every few seconds. My troubleshooting subroutine took all of about 3 dimming cycles (or about 20 seconds) to come up with the diagnosis: the aux fan had seized and attempts to start it were causing a severe (but momentary) load on the electrical system. To confirm my diagnosis I got out of the car, walked around to the front and watched the fan briefly move and then grind to a halt.

To avoid destroying the normal speed relay contacts I turned off the air conditioning and headed home with a keen eye on the coolant temperature gauge (buffered by the DME or not, it would be the first indication of an overheat). Fortunately the outside temperature was low enough and I was moving fast enough to keep the engine cool, so I never did see the interior lights dim again. Back home I pulled up my own Aux Fan DIY, clicked on the link I provided for the Koala Motorsport replacement fan, and had one on the way in a few minutes.

Today I replaced the fan in a couple hours. There's not much to report, as this job remains pretty simple, but I did have a few problems reinserting the upper two screws that hold the fan assembly to the front support because of the angle at which I approach them with the ratchet extension through the grills. To make installation easier I enlarged the relief in the molding of the fan housing on the driver's side so the plastic edge was less likely to interfere with the screw perched on the end of my socket. That worked like a charm and I highly recommend that modification. I also drilled a small hole in the fan frame near where the electrical harness exits so I could use a ty-wrap to secure the harness.

I'm not sure when the original fan failed (I have long speculated that it was dead for almost a year before I realized it was seized) but I replaced it in 2008 with the same Koala Motorsport part I used today. That's 8 years in service by my calculations, so it's fair to say that the aftermarket unit lasted as long if not slightly longer than the factory part. BMW appears to have reduced the retail price of the fan from $650 to roughly $350. I've been around BMW long enough to know that they never do this unless their supplier dramatically reduces their prices. While I don't know where the OE fans are made these days I'm speculating that they are no longer made in Europe or any other "high rent" district. It would not surprise me that BMW gets their fans from the same supplier in China where I speculate the Koala Motorsport unit is sourced. In any case, 8 years is a reasonable lifespan so I still consider the aftermarket part money well spent.

Mileage: 259610