Aux Fan Switch Question

[Weekend Guy]

I have a 03 525i that i did a head gasket on . The engine is back together and running great and compression is good. I noticed my aux fan never comes on. I want to take out the clutch fan and do a electric fan conversion. I plan to use a pwm controller. What i was wondering is how the aux fan switch works . If i can I would like to use the signal from it to turn the fan on . I have read that it is a dual temp switch 91.c and 104.c .I would like to use it because it is already there and I wouldn't have to open the system anywhere else . The controller already has a ac line to turn the fan on with the ac. Can this be done. Thanks for any input.

[DennisG01]

You might be making more work for yourself than needed. The Aux fan IS an electric fan. Some have reported that they have had good luck running only the Aux. Given your location, that might work for you, too. Personally, I like having both the clutch fan and the electric fan. But take the clutch fan off and drive around for a while and see how it does. I did it for a year. You certainly (shouldn't if the cooling system is up to snuff) won't have any problems in the winter.

For what it's worth... don't remove the clutch fan thinking you're going to gain noticeable HP - it's extremely minimal, at best.

[edjack]

You could try using the PWM signal to the fan. However, I have no idea of how much extra load (aka fanout) the DME can provide to the additional controller, or even if the signal is compatible. Read this thread: https://www.bimmerforums.com/forum/s...-Aux-fan/page2

BTW, on your car, the aux fan is controlled directly by the DME; there are no relays. The DME gets a signal from the sensor in the radiator outlet and decides how fast to run the fan, based on coolant temp. The dual-temp switch of which you speak was used on early cars, and provided two speeds via relays.

You will need to provide a separate signal to your fan controller.

If your fan never runs, the outlet temp sensor has failed.

BTW, why are you futzing with this arrangement? A serviceable clutch on the mech fan is all you need, and it provides a fail-safe backup to the electric fan. See also post #2.

[geargrinder]

Yep. Factory Aux is PWM. Because its purely a driver-signal it shouldn't be very loaded down as-is, as long as your new fan is high-impedance it would probably work to drive both.

But then both fans would be just in total parallel.... normally you'd run them staggered so they don't both come on at once all the time. Better to have your new fan run just before the setpoints for the factory Aux... ideally. Yes the car will run fine w/ just the factory Aux tho' - I run a supercharged V8 that way and its happy as clams with the arrangement, even running AC in 90's temps. But a lotta guys like the idea of a redundant so... whatever you wanna do.

[JimLev]

I replaced my clutch fan with a 16" Flex-a-Lite low profile fan mounted in the OE shroud. It's powered by a PWM speed controller that I built. The fan runs as soon as the engine starts at 1/4 speed. You can hardly hear it. There is a temp sensor that will up the speed when required. It also has an off delay that keeps the fan running for 5 min after I shut the engine off to help remove heat under the hood so all the plastic bits around the engine will last longer.

[philly98540]

I replaced my clutch fan with a 16" Flex-a-Lite low profile fan mounted in the OE shroud. It's powered by a PWM speed controller that I built. The fan runs as soon as the engine starts at 1/4 speed. You can hardly hear it. There is a temp sensor that will up the speed when required. It also has an off delay that keeps the fan running for 5 min after I shut the engine off to help remove heat under the hood so all the plastic bits around the engine will last longer.

Hey Jim, did you get that same delay timer I did or did you get a different one? I curently have mine set for an extended 8 minutes after shutdown. I love having it run to help flush out the extra hot air from the SS headers.

[Weekend Guy]

My auxiliary fan never comes on even when the ac is running. The engine temp in the onboard display topped out at around 93.c . I Don't plan to use the DME pwm signal . The controller I plan to use has it's on pwm operation. At the set temp it has a soft start and ramps up to 60% and by 10.degree over the set temp ramps up to 100% speed. I think my aux fan is shot and since I have to replace it . I might as well get rid of the clutch fan.

[JimLev]

Hey Jim, did you get that same delay timer I did or did you get a different one? I curently have mine set for an extended 8 minutes after shutdown. I love having it run to help flush out the extra hot air from the SS headers.

Chris, no I built my own out of a few parts I had on hand. It is wired into my PWM controller for the fan and mounted in the same box.

[BimmerBreaker]

My auxiliary fan never comes on even when the ac is running. The engine temp in the onboard display topped out at around 93.c . I Don't plan to use the DME pwm signal . The controller I plan to use has it's on pwm operation. At the set temp it has a soft start and ramps up to 60% and by 10.degree over the set temp ramps up to 100% speed. I think my aux fan is shot and since I have to replace it . I might as well get rid of the clutch fan.

The aux fan is not always on when A/C is on with PWM fan systems. It will come on when the coolant temperature is at a certain temp as well but I'm not sure that temp off hand and I know my fan usually isn't on when idling but will self-regulate the coolant temps without the fan coming on. So it not coming on in these circumstances isn't necessarily indicative of an issue
Use INPA or ISTA or something similar to turn the fan on, then if it doesn't come on, you have a problem

Also, assuming the aux fan is not working I think that logic is a little dangerous - my aux fan isn't working, so I should remove the mechanical fan that is saving my car from overheating. I'd at least verify WHY the fan isn't working before removing the mechanical fan. If for instance the wiring is causing the issue then wiring another fan to that system may not be the best choice

The dual temp switch setups were also in the earlier cars. Yours with an M54 uses a sensor in the lower radiator hose to determine actual radiator outlet temp which it provides to the DME to determine if the fan needs to be on.
From QSilver...




As the last part mentions, it does run a brief (very brief... the fan will basically sputter to life, then immediately stop) test at startup. You could have someone start the car while you look at the fan.
The car will also throw codes for the fan if it fails the startup test. So you would be best off looking at the car with INPA as you can both check for the electric fan code and use it to directly power the fan to test it's operation...

[Weekend Guy]

I will give that a try. I have done my homework on most of this and I do get a signal from the DME but the fan doesn't run and doesn't test run on start up. I have read about a few people removing the clutch fan with no problem. So I thought installing an electric fan with pwm control would work. I can always just replace the aux fan. I just read about the clutch fan exploding and doing major damage. My 07 550i only has a electric fan and rarely does the aux ever come on

[edjack]

My 07 550i only has a electric fan and rarely does the aux ever come on.

How do you know? Do you have a camera trained on the fan?

[Weekend Guy]

Put It this way. I have left it idling for long periods of time with the ac on and even after driving it hard .I have rareiy had the aux fan come on.

[Weekend Guy]

I thought the aux fan was bad . I confirmed this today. I had to replace the alternator in the 550i and since I had to take the fan out anyway . I use it to test the 525i. Since they have different plugs i made pigtails and plugged it up and it ran in every situation that it was supposed to. Took out the old fan and took it apart and it was corroded. New one on the way also going to replace the clutch in the other fan. Then everything in the cooling system will be new. Thanks fo all the help.