68FB

I installed a new genuine BMW auxiliary fan after my old one crapped out (code 35). The new one is incredibly noisy and annoying the hell out of me. It runs most of the time even on mild days with the A/C off.

I considered just pulling the fuse since I hadn’t even noticed the old fan had crapped out. After I saw the code, I started paying more attention but the only effect I saw was the A/C didn’t work as well at idle. And that was during our recent hot spell, with temps around 90 F.

I found the 50 A fuse behind the glove box but it is a bit tricky to remove so I backed out.

I couldn’t find any info in WDS or TIS on when this fan is supposed to stop and start so I did some checking and I am now wondering if the aux. fan isn’t actually the “main” fan and it is normal for it to run most of the time, just that now I am hearing it.

What I found was the aux fan comes on (A/C off ) when the rad-out temp (ROT) gets to ~72 deg C and it doesn’t switch off until the ROT gets down to a very low ~40 deg C. So once it’s on, it can run for a long while, especially around town. The only way I could get it to turn off idling in the driveway with the ambient about 22 deg C was by spraying into the fan with the garden hose.

I used the fan activation function in AE Scantool to force the fan to run at 30, 60, and 90% speed and estimated the fan was running about 40%. That was surprising because judging by the noise, I thought it was running flat out.

I read the engine-out temp and the rad-out temp with Scantool and confirmed them with an IR gun so the two temp sensors seem to be OK.

After the fan shut down at 40 deg C, it didn’t take the ROT long to get back up to 72 deg C and the fan to restart because the clutch fan is doing virtually nothing. I could stop it easily with a newspaper and it was hardly moving any air. I suspected the clutch was bad so I replaced it it made no difference. It still free-wheels at normal temps at idle.

TIS says the “fan coupling” (which I assume is the clutch) “switches on” at 95 +/- 4 deg C and “switches off” at 60 deg C. So it seems to me the electric fan does the cooling at city driving speeds, air from the car’s movement does the cooling at highway speeds, and the clutch fan only kicks in when things get too hot. This seems to fly in the face of conventional wisdom.

So either the aux fan normally runs a lot and I just hear it a lot more now, or the electronics of my new fan are bad and it is misinterpreting the PWM signal from the DME, or my rad is plugged and the rad-outlet temp is higher than it should be (but I am having no overheating problems.).

Anyone have any any insight?

BrendanSC

I have noticed the same thing. I replaced my aux fan a couple of months ago and it comes on early and hardly ever goes off.

I have replaced my 'main' fan with an electric unit and that comes on at about 88C and turns off at 79C. The fan I have (part of the RK kit) is so powerful that it doesn't take long to achieve this drop, so it only runs occasionally.

The aux fan does most of the cooling on my car now and I'm thinking it always did. I thought about deleting it and having a relay turn the big fan on when the AC is running. But that fan is a lot more noisy than the aux fan so maybe not

68FB

Brendan, is your new aux fan noisy? Is that why you are noticing it hardly ever goes off?

Was it a BMW part?

Sailor24

Bingo I would say the same thing and did a few times but found I should have put on my fire suit. The genuine fan is load too? The aftermarket ones are too. Guess that is why we have good stereos.
I quieted mine down a bit by sanding the leading and trailing edge thinking it was poor workmanship. A lot of work with only a small gain, but it did help.
Did you get an OEM fan clutch because yours seem to be different than mine. Mine is hard to stop most of the time, but I don't think I have heard it fully engage.

jfoj

I know that the Aux fan is definitely controlled by the AC high pressure transducer in most BMW's. It may also be controlled by other factors as well, but I know for sure if you increase or overcharge the AC in one of these cars the Aux fan will start to work and much faster.

Mine never seemed to come on, my AC was a bit low, once charged up to what appeared to be the proper level, the fan started to run faster and be louder. Very similar system in my GMC Yukon as well. Is also partially to to the behavior of the AC systems and the variable output compressor as well.

One thing I find over and over again, many fan manufactures do not get how to make a quiet fan. Even width and spaced blades are WAY louder than partially staggered blades that usually have 1 blade a bit wider. It is unbelievable how much quieter a properly designed fan blade can actually be. No more school bus/trash truck sound from under the hood.

If anyone has their original fan, you may want to carefully compare blade spacing and widths.

Also not sure, but INPA may give you insight to the Aux fan speed, I do believe it will give you AC high side pressure output?

68FB

Damn, so your saying this is normal? That fuse is coming out. What a waste of $400.

I never heard my original fan and it did run so either it was better designed or it never worked properly and eventually degraded badly enough to bring the 35 code in. When that code came in, I started watching it and all it would do was twitch.

Yes, I got an OEM fan clutch.

Sailor24

I don't know if it is normal but when I get in towns and things it comes on. I am on the highway most of the time. I can tell you it turns off at IIRC 80kph. When I am in TO mine is like yours.
I never got a 35 code but mine was clearly done. Did you take yours apart.
You might need part of the fan intact to get the code.

68FB

My testing was done with the A/C off to take that variable out of the picture.

I agree that this is probably a poor fan design problem. OEM's insist on high quality parts when they are building cars but in my experience, their standards drop significantly when farming out short-run spare parts manufacture to suppliers.

I still have the old fan. I'll compare the two.

SleeperE39

+1 on that.

From the technical manual -

Auxiliary Fan Control

The Auxiliary Fan motor incorporates an output final stage that activates the fan motor at
variable speeds.

The auxiliary fan is controlled by the MS S52. The motor output stage receives power and
ground and activates the motor based on a PWM signal (10 - 100 Hz) received from the
MS S52.

Similar to the aux fan in the E46 with MS 42.0 control, the fan is activated based on the following
factors:

• Radiator outlet temperature sensor input exceeds a preset temperature.
• IHKA signalling via the K and CAN bus based on calculated refrigerant pressures.
• Vehicle speed.
• Battery voltage level.

When the over temperature light in the instrument cluster is on (120OC) the fan is run in the
overrun function. This signal is provided to the ECM via the CAN bus. When this occurs
the fan is run at a frequency of 10 Hz.

Since your fan is coming on early and staying on - I'd say there is something wrong with the refrigerant pressure sensor.

I've replaced my Aux Fan with an ebay special - it is louder - but not too bad.
I agree that there is a lot of science behind the fan noise.
With my SPAL and the Aux fan on - it can get quite loud - but no more so than most modern cars in the summer.

68FB

I saw those pics of yours before, so when I took mine apart I was looking for some charring, but there wasn't any. Looked pristine.
I can see why the DME just gave up on yours.