Summah-2018 540i Aux-fan-only observations

[geargrinder]

As has been covered many times around here, some minority of us are heretics and run only the Aux-electric fan on the 540i. Scandalous I know.

A slightly different take on this this time - I have had a bunch of time running around in the heat lately including the heatwave we had back a few weeks ago, and tried to observe just where the initial signs of actual limits of the cooling system seem to be.

This is an old topic but of course its a 'charged' one so I am sure some of the sky-is-falling you're-an-idiot your-engine-is-going-to-assplode pedantic wankers will want to ring in.
For the record (most of which I've said 100x elsewhere...):

• I see nothing wrong with having dual fans for failure redundancy if it makes you sleep better. That was my original plan. If you like 2 fans that's great and I support your lifestyle choice. Go to town. I'm not telling everybody to do this. Do whatever you want. Just don't make up facts based on what you think they 'should be', when we do have actual facts to observe.
• In the case of the blower kits, the extra space of the visco-delete is actually truly helpful and useful (as opposed to using the visco-fan-spacers and still having no clearance down there). For normal motors its less of an advantage. Prob without the supercharger I'd still leave a visco fan on the car.
• "The aux fan isn't engineered for..." is clearly false. It holds up great. Not that it can't and won't fail eventually like any part, but, this part is a pretty ruggedized fan. Anecdotally actually Aux fans seem to fail more on cars that never use them TBH - "I never use the AC / my Aux fan never comes on but now its seized". (admittedly tho' that might be just anecdotal impression)
• "Cars can't survive on one fan" is silly, since plenty of new cars have a single electric fan system. Clearly it is a valid engineering choice.
• The fan increasingly doesn't do anything starting around 30-40mph roadspeed. So no, even if the Aux DOES fail, it doesn't mean you are de-facto stuck on side of the road. With a route that allows highway speeds, you could drive all day with no fan.
• Yes if I lived in someplace Southern where its crazy hot year round and where I ran the AC all the time I would certainly probably install a 2nd electric fan, both to ease the load and provide redundancy.
• Yes on hot days when I'm sitting in traffic, probably my AC isn't as cold as it might be with more fan-age. Another reason for the previous point.
• Gotta say it again cuz people are gonna miss it: I see nothing wrong with having dual fans for failure redundancy if it makes you sleep better. That was my original plan. If you like 2 fans that's great and I support your lifestyle choice. Go to town. I'm not telling everybody to do this. Although I'm not saying not-do-it-either

Car configuration, for those who don't know me:

• M62TU with VF supercharger kit, manual transmission
• Factory M62 radiator
• 88C Euro 740D non-MAP thermostat
• Terraphantm DME tune mods to support 88C t-stat
• Coolant alarm set to 115C (factory overheat alarm is 130C for V8)
• Haven't had a 2nd fan in 4 years. Drive the car w/ the blower in up to triple digits. Use the AC when I want. Car is not assploded.

Below is what I seem to observe, based on a rough indication of how far off dead-center the coolant gauge moves.




I could be more scientific and try to log actual coolant temps vs ambients etc. etc. but this generally this is the picture.

Don't get too agitated by the dark-orange box, at no time did the engine temp trigger my lowered coolant alarm, i.e. hit the 115C.

Naturally w/ the slightly bigger core M5 radiator, or, even better a Zionsville or something, you'd probably do even better.

[Mannyf540]

Nice job GG, you actually got some metrics on this!

[geargrinder]

Yeah... like I said... not exactly scientific but i did try to make some structured and repeatable observations...

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Also Manno - sorry... just replied to your PM...

[tptrsn]

Interesting my dude, so glad you did this!!

I can maybe add a datapoint, since I am another heretic, who is even dumber than you are. Wanna argue with me about who is dumbest and then each of us try to prove we're dumber than the other guy? That would probably be a lot of fun had by all, including the observers. Haha..

Anyway, I have been driving my 540 in the somewhat oppressive dog days of Michigan summer where we hover in the upper 90s or low 100s with extremely high humidity. When I say driving, I mean:

1) daily driving with A/C always on, AND more importantly

2) driving the car at the drag strip where you make a run (~13 seconds of full throttle averaging over 500hp throughout) and then stop and go traffic in the staging lanes to get back up to make another run. Lots of times when it's super hot out I do pop the hood, mainly to mitigate some of the heat soaking of my MAT sensor that is screwed into the aluminum plumbing just in front of the throttle body.

3) a couple drifting events where a run lasts around a minute, and it is largely rev-limiter banging for much of that time. Average power output is not as high as a drag strip run since there is a lot of throttle modulating to manage angle, but the problem is that the vehicle speed through the air is lower, so cooling potential is reduced. Also, I believe that the incessant high RPMs hinder cooling because the coolant is moving through the radiator too quickly.

Having said those things, the reason I am even dumber than you is not because I drive dumber -- although that is probably the case since I just can't imagine anyone else driving a 540 like this -- but because I don't have any sealing between the top of my A/C condenser and radiator. I have noticed hot air oozing out of that area when the aux fan is running on high, so I plan to remedy the situation as soon as I find the correct material candidate to jam in there. Here's my setup so anyone who hasn't seen it in my build thread can see what I mean:



I have an 88deg non-electronic thermostat in the car that I think was from an M60(?) courtesy of Philly Chris (THANK YOU Chris!), and also thanks to information courtesy of him I was able to purchase the aux fan switch for a 318i and install it in place of the OEM pre-TU 540 one. That switch is what brings everything together so that I also have not experienced any CLTs above 104C. Previously I did see some temps over 104C that I didn't like, although I don't think they actually caused any trouble. Seems like maybe I saw temps approaching 120C at times before?

Interestingly, I have noticed like Chris has, that the aux fan runs on high speed a fair amount now with this lower temp switch in it, and personally I don't think it EVER did before. It's somewhat noisy on high, and I suspect that is why the high speed temp threshold was set so high for the 540s, since it is probably unseemly for an "executive's car" to be making that kind of racket.

All in all, my experience supports everything you're saying 100%. It may have been you who enlightened me way back when to the fact that it was possible to run with aux fan only, and that certainly has helped me immensely to do all of the nonsense with this car that I have done, so thanks also to you, geargrinder!

[philly98540]

Heat maps! Nerd! Love it.

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Just saw Thads post. Agree 100%. The loweer temp switch makes the high speed come on sooner to better match the lower temp stat. Works perfectly.

To add some data, in 95 degree heat, very humid, ac blasting full, car totally heat soaked, I see just over 100 C on Ktemp in stop and go. this is with two fans running balls out and my intercooler in the front of the stock rad.

[geargrinder]

Ha ha yes! You're another solid proof-of-concept datapoint, as is DannyZ out in "AC-for-lyfe" country.

As to the 'refinement' factor... for the TU motor, the Terra mods to the tune are REALLY helpful as they take the Aux PWM profile down from that super-high kinda all/nothing programming, and make it more progressive... Now in fairness it WAS indeed calibrated to be the '2nd fan if the visco isn't keeping up', but this makes the Aux far more 'normal' and pleasant for DD use. Before I got that it'd be a bit more unnerving as it kicked in and out harder...

Now that I have his tweaks I could of course further tweak them myself, and if I did run the fan a little HARDER, well probably I could bring some of those initial temps reactions down again... but the overarching takeaway for me is that really ~104-5F+AC+stop&go = the point at which really this system starts to hit its limit. Mitigate any of those 3 factors and you're fine, and, if you do anything to increase the temperature radiation capacity of the system (bigger rad, more fan) then you'd be good for even more than that.

[Mannyf540]

Will that lower temp switch fit the TU ? ( part number?)
I remember thinking if I could use a lower temp switch to work in unisom with the lower temp thermostat I’m running on my TU.

[geargrinder]

The TU uses a temperature SENSOR that feeds the DME that then drives the fan via PWM (aka continuously variable speed)

The pre-TU is a SWITCH that activates the fan, so its more of an on/off thing (although 2-speed? guys?)

So if you were to retro-that you'd have to disable the whole PWM situation.

The easy way to adapt the TU to the thermostat is - as I've assplaned above - do tune tweaks to the DME to activate it at lower temps and more slowly... Terra can help you w/ that as long as you have a DME flashing cable/software.

[tptrsn]

Yep, 2-speed switch. The factory 540 one rarely uses high speed, and the 318i one uses it a LOT. The switch screws into the upper rear of the passenger side radiator end tank.

Speaking of which, I should add for data purposes that I am running a fresh Behr South Africa made 540 radiator, and that my intercooler sits in front of the lower almost half of the aux fan. It's far from an ideal situation for cooling, and yet it works fine:

Intercooler Exposed.jpg

Intercooler Behind Bumper Support.jpg

[AusE39er]

Interesting, as I'm not a fan of the clutch/fan set up.

I was thinking removing of the stock set up and installing a nice SPAL fan directly onto the radiator via plastics "thru rad" mounts.

Yes this would not work as efficiently as stock as it wouldn't make use of the ducted design of the fan shroud.

And I'm aware of what others had done, mounting to the fan shroud. But BMW plastics plus a fan hanging off it plus time could equal disaster.

I'm just wondering if the radiator could support a fan hanging off it, the way my old Falcon could?

Cheers for investigating.

[geargrinder]

Actually a lotta guys have done that without issue. Sometimes they use underspec'd stuff but sometimes its fine, the shroud seems really pretty robust.

You could try the through-rad mount but honestly I'd be FAR more worried about the rad being damaged in that case than the shroud mount.

Been thinking about the whole thing a lot lately and how the Jegs/Summit flat-plate-shrouds really compromise radiator flow vs the big volume of the OEM one. Especially under conditions where you're driving the Aux fan and/or are at highway speeds. The 'front shroud' on the radiator is very clever with those check-flaps that let air flow in but not backwards, so that when the cavity is pressurized by the Aux fan, the air can only flow out the back. With a Jegs/Summit type, under 'pressurized' operation, the effective rad surface area is way down I bet.

Ideally in dual-electric situations you'd have a rear shroud that did the same thing as the front - with check-flaps that would open up during 'pressurized-operation' but seal up during 'suction-operation'.

So the ultimate fantasy rear-shroud is probably a factory-like shape (decent sized cavity behind the radiator), but with exit-flaps, metal reinforcement, and a low-pro suction fan.

In reality, for my happy-Aux-only setup, an improvement would probably be just a near-total rear-shroud delete, as there's no reason to be funneling the outflow anymore. I still have an M5 shroud around here that I might slice and dice up to make into an 'empty shell' ... as long as I can wangle the S62 expansion tank to fit in front o' the SC...

[s13flyboy]

Geargrinder, awesome post! Love the data.

I have a single fan/aux fan question, that I think would be appropriate here. Could you use a different fan motor with the aux fan PWM wiring on the chassis and tweak the DME for it?

For example the Taurus/Lincoln PWM fans that are popular in other platforms, or the e60 single fan setups.

I have used the taurus two speed fan in my 97 using the aux fan wiring and medium/high relays and using a modified stock shroud. Great single fan cooling, with no overheating.

Now in my 01 with PWM I’d Like to reuse this setup but with a PWM motor so I can open up some room in front of the core support for intercooler goodness (not deadpool worthy because it’s a six, but hey, still turbo e39!)

[tptrsn]

Complete rear shroud delete here. Working well, obviously.

As an alternative to "proper" shrouding for an aftermarket puller e-fan, I wonder what the effect would be to just slap a fan or to directly to the back of the radiator like some do. In that way conceivably the air at least gets pulled through the areas where the fan's circle is, and there is no flow impediment for highway running, etc. Probably only one way to really find out how well it would work, but I would think it should be better than nothing...

[geargrinder]

Could you use a different fan motor with the aux fan PWM wiring on the chassis and tweak the DME for it?
...
Now in my 01 with PWM I’d Like to reuse this setup but with a PWM motor so I can open up some room in front of the core support for intercooler goodness (not deadpool worthy because it’s a six, but hey, still turbo e39!)

Yeah... I"ve thought of that too.

The thing is (as you'd expect) the DME obv doesn't DIRECTLY drive the aux fan electric motor... there's apparently an onboard/built-in driver circuit.

As the BMW doc says:

Electric Fan

Vehicles with M62TU, S62 and M73 engines feature a viscous fan as well as an electric fan. The electric fan cuts in when the cooling capacity of the viscous fan is no longer sufficient.
The electric fan is activated by means of a power output stage directly on the fan motor. The motor control module activates this power output stage by means of a square-wave signal with duty factors (variable pulse width) between 10 % and 90 % thus controlling the various speeds of the electric fan. Pulse duty factors less than 5 % and greater than 95 % do not trigger activation but rather they are used for fault detection purposes. The power output stage features its own positive and ground supply.
The fan speed is influenced by the coolant temperature at the radiator outlet and the pressure in the air conditioning system. The fan speed is reduced as the vehicle speed increases.
If a fault occurs during operation a corresponding fault code will be stored in the fault code memory of the DME control module.
For the purpose of checking operation and troubleshooting, the diagnostic program offers the option of activating the electric fan directly via the DIS tester/MoDiC.

As long as the new fan has the onboard driver circuit, and takes a low-current driver signal, you should be good.

The Taurus fan looks to have onboard high/low and takes a high-current supply (BTW having looked at innerwebz wiring diagrams for "taurus fan wiring" - theres a lot of TERRIBLE Taurus fan wiring installs out there!! Some of them I'm not sure how they even work in a car, but perhaps the knuckleheads drawing skill is even worse than their electrical theory therefore perhaps the diagrams are just flawed...) So to use that you'd need to fab or buy a PWM driver circuit of some sort.

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Note the fan gets its own full voltage supply, then the control signal.

http://www.bmw-planet.net/diagrams/r...000008971.svgz

This just made me realize something. Guys have tried to "jump the Aux fan!" and declared "doesn't run must be dead". Well according to factory doc > 90% duty cycle (i.e. like from a jumper aka 100% DC) will not result in activation. So... thats basically an invalid test procedure.

[Mannyf540]

The TU uses a temperature SENSOR that feeds the DME that then drives the fan via PWM (aka continuously variable speed)

The pre-TU is a SWITCH that activates the fan, so its more of an on/off thing (although 2-speed? guys?)

So if you were to retro-that you'd have to disable the whole PWM situation.

The easy way to adapt the TU to the thermostat is - as I've assplaned above - do tune tweaks to the DME to activate it at lower temps and more slowly... Terra can help you w/ that as long as you have a DME flashing cable/software.

Thanks for that info. GG, I’ll have to get with Terra to square that away!!

[s13flyboy]

Haha, yep there are some hack jobs out there. I believe that those are just the two stage ones like the one that I’ve already got.

There is a different “single wire” PWM Motor out there. I’ll have to see if it has the onboard circuit like the BMW unit.

Thanks for the info, I’ll report back my findings.

[AusE39er]

Actually a lotta guys have done that without issue. Sometimes they use underspec'd stuff but sometimes its fine, the shroud seems really pretty robust.

You could try the through-rad mount but honestly I'd be FAR more worried about the rad being damaged in that case than the shroud mount.

Been thinking about the whole thing a lot lately and how the Jegs/Summit flat-plate-shrouds really compromise radiator flow vs the big volume of the OEM one. Especially under conditions where you're driving the Aux fan and/or are at highway speeds. The 'front shroud' on the radiator is very clever with those check-flaps that let air flow in but not backwards, so that when the cavity is pressurized by the Aux fan, the air can only flow out the back. With a Jegs/Summit type, under 'pressurized' operation, the effective rad surface area is way down I bet.

Ideally in dual-electric situations you'd have a rear shroud that did the same thing as the front - with check-flaps that would open up during 'pressurized-operation' but seal up during 'suction-operation'.

So the ultimate fantasy rear-shroud is probably a factory-like shape (decent sized cavity behind the radiator), but with exit-flaps, metal reinforcement, and a low-pro suction fan.

In reality, for my happy-Aux-only setup, an improvement would probably be just a near-total rear-shroud delete, as there's no reason to be funneling the outflow anymore. I still have an M5 shroud around here that I might slice and dice up to make into an 'empty shell' ... as long as I can wangle the S62 expansion tank to fit in front o' the SC...

Interesting. I guess the other reason I don't like the shroud mount how it looks with the exposed nuts on the outside. Back to pondering.

[geargrinder]

Interesting. I guess the other reason I don't like the shroud mount how it looks with the exposed nuts on the outside. Back to pondering.

Understood - but that’s easily solved by choice selection of fasteners. Could use stainless truss head screws or socket (Allen) heads or any number of nice looking things. I enjoy picking choice fasteners for stuff that shows actually. Can really make a fab mod look 2x as good.

[computiNATEor]

All good discussion. For the time being in my hot climate (AC for lyfe, as you put it), I’ve chosen to stick with the stick BMW 530i cooling system with a few choice upgrades.

- Stewart EMP stainless water pump.
- E39 M5 radiator. Direct bolt-in for anyone who has the quick disconnect style coolant hoses.
- All cooling system parts have less than four years and <20k miles on them at this point.

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The I6 E39 MS43 DME is just starting to be unlocked over on E46 fanatics for cooler thermostat temperatures and fan activation. There are some neat features that I’ve been watching, but it’s slow progress.

[JimLev]

Understood - but that’s easily solved by choice selection of fasteners. Could use stainless truss head screws or socket (Allen) heads or any number of nice looking things. I enjoy picking choice fasteners for stuff that shows actually. Can really make a fab mod look 2x as good.

I used black fasteners to hold my Flex-a-lite low profile fan inside the OE shroud.

[pleiades]

My car is electrikked-out now with the Summit Racing fan others have written about on these forums, but two things here I'm wondering about. Will the draw from the Summit Racing fan eventually harm my alternator, especially when the aux fan out front is running with the A/C on?

Second, I gather from this thread that if I removed the Summit Racing fan, the aux fan alone might be enough for my car, but considering it's now over 19 years old, maybe a new one would be wise if I planned to rely on it alone?

Putting the viscous fan back in is an option too, but it sounded like a cropduster and I could feel it holding the engine back at times, as when pulling away from a green light on hot days.

[JimLev]

You should be OK.
Is your fan a 2 speed fan? What is the Summit fan p/n you used?

Its always nice to have 2 fans, you never know when the Aux fan will crap out. Nice piece of mind if you have 2 fans.

I didn't like the "crop duster" sound either or the other peeps in the vicinity starring at my car and wondering if there was a 747 getting ready for take-off.

[tptrsn]

Shouldn't the crop duster sound be alleviated by a new viscous clutch? I thought the roaring visco fan sound usually meant your clutch fan was toast.

[Mannyf540]

Ahhhh yes that sounds kills me!!

It’s like having an intimate moment with the wifey and you have a crazed 5 year old banging on your door that wants his mommy.
I’ve dubbed him the cock blocker.

Just like when I’m going to mash on the pedal, I anticipate the glorious sound of the M62, and all I hear is an International bus at full throttle.
Kids even run to the curb waving thinking they missed the bus. All aboard !!

[JimLev]

Shouldn't the crop duster sound be alleviated by a new viscous clutch? I thought the roaring visco fan sound usually meant your clutch fan was toast.

Mine sounded like a 747 when it was new, I put up with it for 4-5 years until I put the electric fan in.
Can you imagine the Aux fan at full tilt and then the clutch fan roaring at the same time?