Can't make sense of the aux fan - 540i

[psoma]

Hey all,

So I've just finished replacing every component of my cooling system and am no longer losing any fluid. Yay! What is puzzling me however is the operation of the AUX fan. Stupidly, I went for the cheapest option (TYC) and this thing is LOUD. Like, turns heads loud.

It wouldn't worry me if the thing rarely kicked into high speed, but within 10-15 minutes of driving, the car is up to what I believe is nominal operating tempepature for a 540 (106-108 degrees celcius) - a temperature which is above the aux fan's "full speed" setting.

I've been running the car without the aux fan for the last couple of weeks but it was a hot day today (33 degrees celcius) and the coolant temp warning sounded and my transmission entered overheat protection (Test NR06 read 123 deg cel... yikes!)

Am I missing something here? Surely as these cars run hot by design, these fans can't run at full speed all the time?!? Can confirm viscous fan is running correclty too.

Cheers,

Tom

[larrym3711]

If the temp is really and truly high and you have replaced the major components, it sounds like air is still trapped in the system somewhere. My 540 does not overheat at all even in the hottest part of summer. Soooooo, something is still hindering the cooling. Yes, my aux fan does come on at a low speed for a minute or so, then shuts off for awhile. It does not stay on.

larrym3711
2001 540iA Sport

[rf900rkw]

The aux is not controlled by engine temp, it's controlled by radiator outlet temp. If it's coming in that quickly, and the car is overheating that badly, then something is causing the radiator to not cool.

[andre14]

The aux is not controlled by engine temp, it's controlled by radiator outlet temp. If it's coming in that quickly, and the car is overheating that badly, then something is causing the radiator to not cool.

bingo. make sure your system is bled properly. your operating temp can be as high as 108 celsius and you should not have the aux on (and certainly not on its highest speed) unless you're running with your ac on.

[edjack]

You should have the DME-controlled aux fan, with just three wires attached. Since you went for the cheapest option (TYC), perhaps the controller on the fan housing is not working correctly.

I have the older fan setup (original fan), and I have never noticed it switching on in summer, unless the A/C is on, and then it's at the low speed.

[rdl]

Hey all,

So I've just finished replacing every component of my cooling system and am no longer losing any fluid. Yay! What is puzzling me however is the operation of the AUX fan. Stupidly, I went for the cheapest option (TYC) and this thing is LOUD. Like, turns heads loud.

It wouldn't worry me if the thing rarely kicked into high speed, but within 10-15 minutes of driving, the car is up to what I believe is nominal operating tempepature for a 540 (106-108 degrees celcius) - a temperature which is above the aux fan's "full speed" setting.

I've been running the car without the aux fan for the last couple of weeks but it was a hot day today (33 degrees celcius) and the coolant temp warning sounded and my transmission entered overheat protection (Test NR06 read 123 deg cel... yikes!)

Am I missing something here? Surely as these cars run hot by design, these fans can't run at full speed all the time?!? Can confirm viscous fan is running correclty too.

Cheers,

Tom

You can see details of circuity and a description of operation for a 1999 model year here
http://wds.spaghetticoder.org/en/e39...ronics_ME7.2)/

I'm not sure what you are describing.
A) is the electric fan at running high speed continuously? Or is it not running when you expect it to when engine temp is ~106C?
B) does "running the car without the aux fan" mean you have disabled the fan?

FWIW, the aux fan on my 6 cyl (probably smaller than your V8) is loud too at high speed. Although subjective, I could describe it as very noticeable, even headturning loud.

Regards
RDL

[Cyrix2k]

I don't think the fan is at fault, it sounds like you have other issues. My fan is also head turning loud, but it never comes on unless the a/c is on. I assume it's factory.

[peter540]

I also vote for the "need to bleed." Dollars to donuts that's your problem...

[rf900rkw]

Based on the description, I don't think it's a bleed issue. If the fan is ramping up to high speed that fast, and all the electronics are up to snuff, then there is very hot water exiting the radiator. My guess would be an A/c condenser packed full of cicada carcasses.

The other possibility is this aftermarket fan is not progressive as the factory fan, and merely hits high speed at any "on" signal.

[psoma]

Thanks guys, will try to address as much as I can in a single response:

- I run my AC all the time - it tends to be warm to quite hot here most of the year.
- the fan *does* ramp up, low, med, high - but once high, it pretty much stays there.
- guess the point about radiator outlet answers my primary quetion which was regarding engine temp and aux cut in. The rad should cool the water sufficiently by the time it's out the other end, hence outlet temp should not be > 100 or so
- to disable the aux fan, I unplugged it.
- shall try bleeding again...

Cheers,

Tom

[rdl]

Thanks guys, will try to address as much as I can in a single response:

- I run my AC all the time - it tends to be warm to quite hot here most of the year.
- the fan *does* ramp up, low, med, high - but once high, it pretty much stays there.
- guess the point about radiator outlet answers my primary quetion which was regarding engine temp and aux cut in. The rad should cool the water sufficiently by the time it's out the other end, hence outlet temp should not be > 100 or so
- to disable the aux fan, I unplugged it.
- shall try bleeding again...

Cheers,

Tom

The fan ramping up to high and staying there may due to A/C condenser pressure rising, which is common/normal in higher ambient temperatures.
This link (see the WDS link in an earlier post) gives you an indication of aux fan speed vs A/C condenser pressure.
http://wds.spaghetticoder.org/en/zinfo/THP0900SO-6450002.htm

The overheat event was likely due to unplugging the auxillary fan, especially since ambient temps were fairly high.

You can do a check sequence to confirm what is ramping the fan speed:
A) plug the auxillary fan back in
B) start the engine, A/C on, unlock the cluster and enable the coolant temp in the cluster, test #7.0 I think
C) drive around, city speed, to get the engine to temp and A/C pressures up while monitoring coolant temperature (city speed to eliminate highway ram air effect cooling during test, i.e. rely on the fans)
D) when the auxillary fan ramps up to high, turn off A/C and see if the fan slows down over a few minutes.
E) assuming fan slows, turn A/C back on and listen for speed increase as pressures rise again.
F) if engine coolant temp rises over normal ~106 to110C, does aux fan speed increase? Track max coolant temp while aux fan is operating, both with A/C on and off.

If D) & E) does ramp the aux fan speed from/to maximum, it might be worthwhile having A/C pressures read and system checked. At 33C ambient A/C high side pressure should be in range of 20 to 25 bar +/- depending on humidity; which should be ~50% to 75% aux fan speed. E.g. a condenser clogged with bugs will partially block air flow and drive pressures higher than normal.

If engine coolant temp rises over normal and aux fan does not ramp high enough to control it, even with A/C on, bleed &/or have cooling system checked.

Regards
RDL

[andre14]

until you figure out the problem, plug the aux back in. overheating will likely hurt you more than a few odd looks in traffic...

[psoma]

Yeah, have done so.

Interesting development - whilst reading up on the latest Dynavin D99+, I found that there have been issues with the D99 (which I have) and the HVAC - issues with the aux fan being one of them. Will be disconnecting the iBus unit to check.

Cheers all,

Tom

[m5hoot]

+1 out of 2. I agree on bleeding. Easiest way is to get nose of car about 8" above back end and open bleeders carefully. Manual may not say raise front end, but always worked for me on one try. You can also drive up steep ramp.

The one thing I had one time that I want to make sure is NOT your issue is that I had to shim out some plastic pieces in front of aux. fan as something somewhere kept wanting to ever so slightly touch the aux. fan blade sounding like baseball card in bicycle spokes....come on, some of you guys remember! Just make sure fan is noisy all on its own. Look how simple the damn thing is! Little air will really mess you up too. It will likely be more like 2 qts. low once air gets out.

[psoma]

Okies so!

Turned out my primary problem was the trans heat exchange unit / trans cooler being all but blocked. Popped a new one in and not only does the gearbox work properly now (holds gear properly on long drives, can engage reverse when hot and torque converter stays locked) but the fan runs *far* less than before.

It's still louder than I remember it, but I put that down to the fact I bought a cheap TYC piece of crap Hmm.... might put the old OEM one back on actually.

Cheers all!

Tom

[240sxguy]

I put a TYC fan setup on my maxima and that sucker was loud as hell too FYI.

[stija]

Where is the transmission exchange unit? My fan starts running as soon as I turn the car on and ramps up to high/loud speed right away - whether the ac is on or off. I also noticed that ac sometimes runs and some other times does not. Have not figured out the variable that makes it stop working, and when I say working, I mean it does not blow cold air. Then randomly it starts blowing really cold air. This is in regards to my 2000 e39 540i automatic.

[larrym3711]

Interesting as to all the variations for aux fan operation. I too replaced my aux fan two years ago with a TYC fan. However, there were several showing that said they were for my car.....but.......only one fan looked EXACTLY like my old fan. That's the one I got and it worked perfectly (PWM type). Yes, it does get to high speed occasionally but slows down within a minute to any of various speeds with the AC on. It definitely does not stay on high speed for long, even when it's hot.

larrym3711
2001 540iASport

[Lolrus]

Did you ever find a fix? Same problem here

[siny528i]

bingo. make sure your system is bled properly. your operating temp can be as high as 108 celsius and you should not have the aux on (and certainly not on its highest speed) unless you're running with your ac on.

At 108 is when your needle will start climbing up...

[siny528i]

If it's chilly (high 30s - low 50s) outside and your system has enough coolant and its BLED your aux fan is not supposed to kick in because the temp of the coolant in this weather will rarely reach 92C