E39 Aux Fan Upgrade How To

[Brad D.]

E39 Auxiliary/Condenser Fan Upgrade How To

By Bradley Denton

Purpose:
To improve cooling and air conditioner performance by upgrading the 20 year old electric auxiliary fan.


The Fan:
The E39 5 Series has an excellent auxiliary cooling fan installed from the factory. For those that have hear it running on high speed, they will tell you it sounds like it means business. While I have no definitive CFM rating for the fan, I am willing to bet that it out performs most, if not all aftermarket fans on the market. It has a side benefit of coming installed in a very nice shroud with louvers to reduce drag at freeway speeds and improve flow through the fan at low speeds. The fan is roughly 16" in diameter and has curved blades. I am using an OE replacement fan made by DEPO parts for a 99-03 e39.


The Install:
Since I am using a modern parallel flow condenser the install will be slight bit different than if the original condenser was installed. The fan in the e39 is on a 50A circuit which means that the stock wiring for the e28 aux fan will be insufficient as it is on a 25A circuit. New wiring will be required. I wanted to be able to have the fan run on a high and low speed so I planned to use the resistor set that came with the electric fan.
I should note here that I made a bit of a mistake as I learned after sourcing the fan that these model years use a PWM (pulse width modulated) fan control instead of resistors to control fan speed. Only the 97 and early 98 models have the fan with a three speed resistor pack. I removed the PWM controller and installed the factory resistor pack from my old stock fan. I have plans to build a PWM controller for the e39 fan so stay tuned for this upgrade ( I am a strange mechanical engineer and enjoy electronics projects). This configuration will require two relays. Using the original low and high speed fan relays, I wired them to act as the control circuit for a new pair of 50A relays mounted on the core support. Using a run of 2 pair shielded wire, I wired them up. The wiring I used can be seen below.


Wiring schematic (yes, I know, I am type-A and used the original ETM schematic and modified it). There is some optional wiring and it is noted in the drawing.


Resistor Pack Mounted

Two Pair wire for control circuit. You can connect the two ground wires together as shown.

Relay control wires spliced into original fan wiring. Since it is only controlling a relay, the wires do not need to be a large gauge.

Relays and wires mounted and ready to rock.

Since I have an intercooler mounted on my car I had to remove the lower shroud to get it to clear. This would not be necessary w/o the intercooler. Here are some shots of the mounted fan.



Performance and Conclusion:
The fan on low speed seems to move as much air as the old fan did on high speed. Since I want a little bit more performance on the low speed setting I am planning on sourcing a 0.2 ohm resistor from an early e39 to replace the e28's 0.6 ohm unit. On high speed this fan just plain rocks. It moves an amazing amount of air. With the engine off it has enough guts to spin the stock clutch fan with a healthy fan clutch. That's what I'm talking about. It is a bit loud in front of the car, but it is almost not noticeable from inside the car with the windows down (who wants to do that though when you are rocking the AC in 104° heat). All in all I am very pleased with the fan upgrade. It looks exceptionally stock (too bad it's covered by the cowl cover) and performs as I had hoped it would. The only thing I would do differently would be to have purchased an earlier model fan so it had the resistor pack. Now that I have this one though I will be implementing my PWM controller. When (if) I get around to it, I will update this thread. Hope you guys enjoy and give you an option when replacing your aux fan.

[2ndeagle]

Since the new fan much higher CFM, is it necessary to keep the original clutched fan?

[Brad D.]

It might be just enough to keep the engine cool, but with 100 degree weather and the AC on, I don't think it's enough by itself.

[Justin_FL]

Looks good. I know on my 530i that fan moves quite a bit of air and it's quite audible, so I'm sure it will be a great help on the E28 while idling in traffic, which is where the original R12 system on my '86 535i would always pale in comparison to modern cars in 90-100°F ambient temperatures.

[Mike W.]

Interesting writeup Brad. Coming from a couple of FWD's along with E3s and E21s, the stock fan that first appeared (in my cars) on E12s always seemed pretty good sized to me, not that things haven't progressed in the past 30 years, just that the stock seemed ok.

Couple of questions though. I think air moved is largely a function of fan pitch, meaning the depth of the blades, or how much air a blade could theoretically bite off, the number of blades, diameter and of course speed. Anyway, how large is it compared to stock and what is the pitch? I think the curved blades are more a sound thing than function, and I'm guessing the new one is 11 blades? Many seem to be, but like speed, more is better to a point, then it can actually decrease.

[GermanlookT3]

I say we add this to the FAQ section... This is Definately a good writeup! I'll be doing this to mine soon

[winfred]

for a less air raid siren sounding fan that moves a shitload of air score a e32/34 fan, a plus (besides not alerting you to the luftwaffe on approach) the e32/34 fans hardly ever die, the resistor does but it is the same shitty resistor that the e39 fan has two of

[Brad D.]

Interesting writeup Brad. Coming from a couple of FWD's along with E3s and E21s, the stock fan that first appeared (in my cars) on E12s always seemed pretty good sized to me, not that things haven't progressed in the past 30 years, just that the stock seemed ok.

Couple of questions though. I think air moved is largely a function of fan pitch, meaning the depth of the blades, or how much air a blade could theoretically bite off, the number of blades, diameter and of course speed. Anyway, how large is it compared to stock and what is the pitch? I think the curved blades are more a sound thing than function, and I'm guessing the new one is 11 blades? Many seem to be, but like speed, more is better to a point, then it can actually decrease.

You are correct on the factors that affect airflow of a fan. The e39 fan is 16" in diameter which is almost identical to the e28 fan, however it has 10 smaller curved blades whereas the e28 fan has 5 larger blades. I would say that looking at amperage through the circuit is a good indication of the work that the fan is doing. While it's not exact, if you change the pitch of the blades of the same fan to move more air, it will increase the amp draw of that fan. While it's not an apples to apples comparison, the e28 fan is on a 25A circuit and the e39 fan is on a 50A circuit.

[BimmerDan]

Does anyone happen to have the photos that were in here before the photobucket jerks?

[02stu]

I just completed this on my 84 533i, I don't have any pictures but if you have a specific question or need a specific picture I can help you out

[BimmerDan]

Stu,
I was looking for the e39 wiring schematic, I think I'm going to wire for high speed only to a switch until I have ac. I need more of a extended idling fan.

I could Google it too, just went to print this off last night.

Thanks.

[dcains]

I just completed this on my 84 533i, I don't have any pictures but if you have a specific question or need a specific picture I can help you out

Did you buy a used OEM fan, or a new Chinese-made knock-off from eBay?

http://www.ebay.com/itm/Bmw-5-Series-E3 ... Un&vxp=mtr

[BimmerDan]

Good point.

This is the one I purchased
Bmw 5 Series E39 528 540 I 97 98 A/C Ac ... BzbCYNQVJ1

[tig]

I'd be interested in this thread if the photos worked. Dead to me without them

[vinceg101]

Same here. In for more info.

[02stu]

I'd be interested in this thread if the photos worked. Dead to me without them

It's a shame Photobucket decided to suck even more than it had in the past.

[Dvs]

Hey guys,

This is very interesting thread, i am not good with electronics but i understand the concept and it is worth the effort,
I also have overheating issues here in Dallas Texas, i got my '88 e28 from a guy who did not take too much care of it, the resistor on the auxiliary fan was broken, i replaced it but i wired it wrong so next summer aka this summer i was starting to have overheating issues again, well fixing the wiring on the aux fan did not help, when i turn the AC on, the fan works but the second stage when the engine is overheating does not kick in...i hot wired the system and both stages work but when all is put together...the aux fan never kicks, while standing at the light my car immediately overheats...thank good air cooling is excellent ok the car, i also exchanged the fan clutch, first one was made in china, it barely works, second one was Beer from BabAuto.com, it was broken from the the begging, i stopped the fan with my fingers while the engine was hurting...the third fan clutch is Sachs, even when i slightly touch the gas you can already the "tornado" in front of the car. I also exchanged the temperature sensor in radiator, which i understood is the one that makes the aux fan kick in on the second stage when the water gets too hot in the radiator...the thermostat is also good, bought a new one...boiled it up in the same pot on the stove with the old one...the old opened up much quicker though both were the 80 something Celsius ones...so i did put the old back in with a new gasket, i recently changed the oil, it takes it like a good 3 weeks to go completely blackish...since the engine has like 345k miles on it....it pushes some gas to places where it is not supposed to be...but still there is no water contamination so i guess a head gasket issues can also be eliminated so in conclusion after all these it is still overheating...

I think i will just hot wire the aux fan on first stage to run non stop since my AC is out of order...
But i am open to other suggestions...