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Thread: Aux fan wiring question 1999 540i

  1. #1
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    Aux fan wiring question 1999 540i

    Does anyone know if the dem supplied 12v or ground on the trigger wire that goes to the fan harness?
    http://www.bimmerfest.com/forums/sho....php?p=5301847 <--- wire diagram in post #5 for reference.

    1998 bmw 540i 6 speed, JBrace flyweel with clutchnet clutch, K&N cold air intake, Super Spirit exhaust, Dinan Stage 2 software, 3.15 rear,
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    It's a PWM signal.


    /.randy

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    Basically it's a square wave that changes frequency to increase/slow down the fan speed.







    Last edited by JimLev; 05-23-2014 at 05:28 PM. Reason: forgot pics

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    Thanks for the answers, I ended up hard wiring the Taurus fan to the ignition. I live in the south so. It needs to be on at all times anyways l. No aux fan, no mechanical fan with the Taurus fan running on low speed The motor never gets hotter than 215 on a 95 deg day.

    1998 bmw 540i 6 speed, JBrace flyweel with clutchnet clutch, K&N cold air intake, Super Spirit exhaust, Dinan Stage 2 software, 3.15 rear,
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    I wonder if the PWM aux fan will run at full 100% duty cycle or at a maximum of 95% in emergency situation?



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    Not sure where you are going with the 95% versus (say) 100% duty cycle ( like in the 'emergency' heat condition?). However, if the airflow is significant (and it is) the difference in heat removal ( or more technically hear transfer) between 95% and 100% fan speed is almost insignificant.

    larrym3711
    2001 540iA Sport

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    What I mean is that when the aux fan has to run at full speed (jet speed) does it run at 100 pwm or slightly less?



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    So this is why the fan circuit always has power? The factory aux fan has circuitry that reads the square wave input and adjusts the fan speed? In my opinion the mechanical fan is crap and the aux fan is unreliable and weak. I suggest anyone with a 540 use the 1990-95 ford taurus fan. It fits behind the shroud perfectly and has more cfm on the low speed than the 2 factory fans combined. I put one in every 540i I sell and they never have cooling problems again...

    1998 bmw 540i 6 speed, JBrace flyweel with clutchnet clutch, K&N cold air intake, Super Spirit exhaust, Dinan Stage 2 software, 3.15 rear,
    BC Race coil overs, Eibach sway bars, Taurus electric fan, Lots of stereo upgrades

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    Yes, that's the way the aux fan works in cars with the tu engine.
    After 14 years and 142K my aux fan is still working fine.

  11. #11
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    A ticking time bomb my friend

    1998 bmw 540i 6 speed, JBrace flyweel with clutchnet clutch, K&N cold air intake, Super Spirit exhaust, Dinan Stage 2 software, 3.15 rear,
    BC Race coil overs, Eibach sway bars, Taurus electric fan, Lots of stereo upgrades

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    Most ticking timebombs I see are home brewed "upgrades". In for pics of the installation, ducting, and wiring.


    /.randy

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    Quote Originally Posted by neonphire8604 View Post
    A ticking time bomb my friend
    I'd venture to say any aux fan (pre PWM) that uses resistors and relays to control the 3 speeds are more prone to failure that the PWM fans.
    I can't count the number of guys I've helped on the various BMW forums I've been on with 3 speeder.
    When my aux fan does fail I'll just turn up the speed a bit on my electric fan until I get a new aux fan.

  14. #14
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    What electric fan do you use?

    1998 bmw 540i 6 speed, JBrace flyweel with clutchnet clutch, K&N cold air intake, Super Spirit exhaust, Dinan Stage 2 software, 3.15 rear,
    BC Race coil overs, Eibach sway bars, Taurus electric fan, Lots of stereo upgrades

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    Quote Originally Posted by neonphire8604 View Post
    What electric fan do you use?
    Flex-a-Lite 16" Slim line version.

  16. #16
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    The taurus 2 speed fan is all the cooling power my cars have ever needed. It works out nice with the older style fan wiring because you can just splice right into it.

    1998 bmw 540i 6 speed, JBrace flyweel with clutchnet clutch, K&N cold air intake, Super Spirit exhaust, Dinan Stage 2 software, 3.15 rear,
    BC Race coil overs, Eibach sway bars, Taurus electric fan, Lots of stereo upgrades

  17. #17
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    Quote Originally Posted by JimLev View Post
    I'd venture to say any aux fan (pre PWM) that uses resistors and relays to control the 3 speeds are more prone to failure that the PWM fans.
    wait - what model of e39 does that apply to? I have an 01 540i/6, and I thought mine was the newer years with PWM but also had resistors...

    Did I mix some things up?
    2001 Aspen Silver 540i6 - 180k mi - 3" DUDMD Tune, aFe Intake, M60 Intake Manifold, Eibach Anti-Sway Bars (F&R), e60 SSK

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    Quote Originally Posted by neonphire8604 View Post
    The taurus 2 speed fan is all the cooling power my cars have ever needed. It works out nice with the older style fan wiring because you can just splice right into it.

    Which speed do you leave disconnected?

    - - - Updated - - -

    Quote Originally Posted by 540iEP View Post
    wait - what model of e39 does that apply to? I have an 01 540i/6, and I thought mine was the newer years with PWM but also had resistors...

    Did I mix some things up?
    01 will be PWM; no resistor pack, just a big honkin' transistor controller.


    /.randy

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    So I've seen how to replace the resistors on YouTube, but nothing on quick fixes for a dead aux fan if its the newer style. My aux fan doesn't turn on with the AC on max. I have the no AC symptom when stopped, but cooold AC when moving. Should I be replacing the whole assembly, or is there a cheaper / less involved fix compared to pulling the entire front off and replacing the aux assembly as a whole unit?
    2001 Aspen Silver 540i6 - 180k mi - 3" DUDMD Tune, aFe Intake, M60 Intake Manifold, Eibach Anti-Sway Bars (F&R), e60 SSK

  20. #20
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    My aux PWM controller is built into the motor of the aux fan. It's not repairable, you need to replace the fan.

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    Aux Fans from 1995-up

    Here's the info (again) about the aux fans used on BMWs from 1995-up. BMW used a 2 stage, 3 stage, and variable speed aux fan. The variable speed aux fan doesn't react like the 2 & 3 stage fans...so don't get confused with it's behavior:

    2 stage Aux Fan: up to 1996 MY



    3 stage Aux Fan: 1996-1998



    Variable Speed Aux Fan: 1999-up





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  22. #22
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    Quote Originally Posted by rf900rkw View Post
    Which speed do you leave disconnected?

    - - - Updated - - -



    01 will be PWM; no resistor pack, just a big honkin' transistor controller.
    I used to have it on low speed and high speed but I realized that high speed was never necessary with that much cfm so I now have it so the speed that receives an input from the AC compressor triggers the fan to turn on. so basicly when the ac is on its always on but with the ac off it uses the temp sensor input on the radiator to turn the fan on.

    1998 bmw 540i 6 speed, JBrace flyweel with clutchnet clutch, K&N cold air intake, Super Spirit exhaust, Dinan Stage 2 software, 3.15 rear,
    BC Race coil overs, Eibach sway bars, Taurus electric fan, Lots of stereo upgrades

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