Crazy Loud Aux Fan 540i

[trevzor4242]

I've had my E39 540i for a few months now, and I'm able to start fixing stuff on it finally. Ever since I've owned the car, when the ac is turned on the Aux fan spins up incredibly loud. It sounds like a jet engine. It's embarrassingly loud. I've been around other cars like mine and I know this is not a normal thing. I drive in 90+ degree weather almost daily and the ac is a must.

Anyways, the car is very quiet with the ac off, but any time it's turned on, within less than a minute that Aux fan is just cranking. It could be quieter but I don't believe the fan is at fault, I think it's just spinning way too fast to be quiet. Because Temps never seem to get high when I drive I struggle to believe it's a Thermostat, water pump related issue. The engine bay always seems extremely hot but all sensors say it's alright.
Has anybody experienced this or know a fix to it? I read something about possibly having too high ac pressure... Maybe it's worth replacing the Thermostat/water pump anyways.

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[purplecty]

I've had my E39 540i for a few months now, and I'm able to start fixing stuff on it finally. Ever since I've owned the car, when the ac is turned on the Aux fan spins up incredibly loud. It sounds like a jet engine. It's embarrassingly loud. I've been around other cars like mine and I know this is not a normal thing. I drive in 90+ degree weather almost daily and the ac is a must.

Anyways, the car is very quiet with the ac off, but any time it's turned on, within less than a minute that Aux fan is just cranking. It could be quieter but I don't believe the fan is at fault, I think it's just spinning way too fast to be quiet. Because Temps never seem to get high when I drive I struggle to believe it's a Thermostat, water pump related issue. The engine bay always seems extremely hot but all sensors say it's alright.
Has anybody experienced this or know a fix to it? I read something about possibly having too high ac pressure... Maybe it's worth replacing the Thermostat/water pump anyways.

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My friend has an 03 540 and his is acting the same even after a tstat replacement...

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[edjack]

We can't help if you don't identify the model year.

[trevzor4242]

It's a 2000 540i m sport.

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[JimLev]

It's a 2000 540i m sport.

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I have the same car as you (a 540 sport, not m sport), it's normal.

[amancuso]

Yup, it's annoyingly normal. I used to have a '99 540i and it did the same thing.

[atobe]

It does sound like a jet when I turn off my car. Don't really notice it when driving though. The 528 does it too, it's when you don't hear it then there's problem, and that's how I found out my aux fan was broken.

[trevzor4242]

I was at a local meet not two days ago and met a guy with a 99 540i who had never experienced anything like this... It's so hard for me to believe it's normal after that. I might record a video just to be sure. That can say a thousand words.

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[computiNATEor]

The auxiliary fan is controlled by the DME, and it will run on a comibination of inputs, including engine coolant temps and AC pressures. It might not hurt to have the coolant temp sensors changed, the HVAC system checked for efficiency (and the condenser cleaned), and the aux fan inspected for bad bearings.

But they’re noisy regardless.

[theWalkinator]

Tstat mod and fan delete!

[Qsilver7]

It's a 2000 540i m sport.

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To help us help you better...it would be a good thing to add your model year to you car info (or create a signature) because there can be different answers/suggestions/recommendations depending on your build date.

For instance, from 1995-2003, BMW used 3 different types of aux fan set-ups for the e38/e39 (I don't follow the 3 series so I don't know what the e36/e46 used). You could have a two-stage aux fan, three-stage aux fan, or a variable speed aux fan. So without knowing your model/model year...or if you just pull up next to another 540 or 740 owner...depending on if they have the M60/M62/M62TU engine...you could have a totally different aux fan set-up:

{Two-Stage Aux Fan}


{Three-Stage Aux Fan}


{Variable Speed Aux Fan}

[JimLev]

The auxiliary fan is controlled by the DME, and it will run on a comibination of inputs, including engine coolant temps and AC pressures. It might not hurt to have the coolant temp sensors changed, the HVAC system checked for efficiency (and the condenser cleaned), and the aux fan inspected for bad bearings.

But they’re noisy regardless.

I bet the area between the condenser and the radiator has 18 years of Midwest farmers crops, leaves, dead bugs, and cigarettes butts packed between them.
Might be a good idea to take a look.

[computiNATEor]

I bet the area between the condenser and the radiator has 18 years of Midwest farmers crops, leaves, dead bugs, and cigarettes butts packed between them.
Might be a good idea to take a look.

For sure. I've pulled aux fans in two of my cars; absolutely amazing how much crud gets stuck in there.

[dannyzabolotny]

Maybe your cooling system is running a little hotter than usual and the aux fan is trying to compensate by going to max speed. Mine did that so I replaced it with a new one thinking it would be quieter (figured I’d put in a new aux fan anyways since mine was original). It wasn’t any quieter but what really helped was reinstalling my clutch fan. That seemed to have brought the overall coolant temps down enough to where the aux fan isn’t always on max speed all the time.

[trevzor4242]

Tstat mod and fan delete!

Elaborate please.

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[trevzor4242]

Thanks for all the insight. It's really helpful knowing what the dme looks at to determine fan speed.

I just checked around the condenser. No major amounts of crud at all, surprisingly clean.

I'm thinking of doing a cooling system refresh anyways because my car runs very hot. Dash gauge is never high but the engine bay always feels very very hot. Like I can barely grab the intake without almost burning myself.
Also worth mentioning my Ambient temp sensor is bad, and just reads - 40 degrees. (part already on its way) Also I get the message to check Coolant however it's always topped off. So I probably need a new sensor there too.

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[trevzor4242]

Just checked today, I found the condensor area to be surprisingly clean. So nothing there.
The car runs very hot so I think I may do a cooling system refresh anyways. The dash gauge never shows high temps but the engine bay is very hot. Always. It's to the point that I can't touch the intake for more than a couple seconds without burning myself. Now I've only had E36's before so i'm not sure if this is just normal for the big v8 but it doesn't seem good.

Also, a couple things worth mentioning... My ambient temp sensor is bad and I'm waiting on the replacement to arrive (dash shows -40 degrees always). Dash also tells me to check the coolant, but I always have it topped off so I believe the coolant level sensor is out too.

[theWalkinator]

Elaborate please.

Replace OEM 105C thermostat with 88C thermostat, and covert clutch fan to electric fan, just search this forum and you will find plenty info on those 2 mods.

[Qsilver7]

Also worth mentioning my Ambient temp sensor is bad, and just reads - 40 degrees. (part already on its way) Also I get the message to check Coolant however it's always topped off. So I probably need a new sensor there too.

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The ambient temp sensor reading -40 can prevent the AC system from working correctly. The IHKA uses data from that sensor to determine ambient temps...which it uses to initiate or turn off some of its features.

See some of the text about the climate control system from the owners manual...and note that it gives specific ambient temps where the IHKA will do certain things. Also see the info about analog signals that the "outside" ambient temp sensor sends to other control modules around the vehicle that operate using data from the sensor. Even the heated mirrors use the ambient temp sensor to regulate its heating cycle. If it reads -40° F all the time, then the mirror NEVER turn off...and can result in burning them out:

[trevzor4242]

Ambient temp sensor arrived today. Seems to have changed nothing but with the fan but it's nice to see the temperature now. I had to go searching for the wire to plug into and found another one with the same connector that has two brown wires. I don't know what it goes to. Maybe someone can chime in on that.
Took a video of the car too: https://drive.google.com/file/d/1Z15...w?usp=drivesdk

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[Luftpost]

I have same car. Same issue.

What I can tell you is that anytime my coolant level drops (randomly and mysteriously), the aux fan comes on more often, for obvious reasons. I check the digital temp readout on the instrument cluster (unlock via last seven of VIN) and it will typically read 101C-104C during these events (90F+ OAT). Anything less than that and its operates normally. A slight coolant top off helps, if needed. You may also have some air in the coolant lines, so do a search under "coolant bleeding".

Operating with A/C on definitely effects the operation of the Aux Fan.

L

[trevzor4242]

I have same car. Same issue.

What I can tell you is that anytime my coolant level drops (randomly and mysteriously), the aux fan comes on more often, for obvious reasons. I check the digital temp readout on the instrument cluster (unlock via last seven of VIN) and it will typically read 101C-104C during these events (90F+ OAT). Anything less than that and its operates normally. A slight coolant top off helps, if needed. You may also have some air in the coolant lines, so do a search under "coolant bleeding".

Operating with A/C on definitely effects the operation of the Aux Fan.

L

I have already bled my Coolant and topped it off so I don't have that issue. When using my obd reader I see the car is maintaining about 220-227°F which is right in the range of the Thermostat.

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