Replacing the clutch fan with an electric one?

[TriX5]

Nope. My '06 4.8is only has the e-fan, not the aux fan. I have one of each, pre- and post face lift. The later car is quite different in many aspects.

[papasmurf]

Originally Posted by romeokc10

If you do find a suitable replacement what about the belt?

The fan is simply bolted onto the front of the water pump. Taking it off has no bearing on the engine belt or water pump. In fact, by taking the weight off of the front of the water pump, it should promote longevity for the water pump.

Originally Posted by TriX5

4.8is has an e-fan.

Originally Posted by Weasel

I was gonna say the same thing... some V8 E53's have an electronic fan OEM, meaning all the stock parts are available for fitment. Control on the other hand isn't pre-wired or anything so you'd have to wire up the circuit yourself.

Really? I'm going to look into that for sure. That's probably right where the 4.8 gets a bit more power from as well. As for wiring, I was planning on wiring up a relay and having the fan kick on with ignition anyway. It's the safest bet and idiot-proof.

The radiator, if I measured correctly, not counting end tanks, is 23" X 23" wide. The front aux fan, not counting the outer reinforcement, is about 17" diameter. The engine fan, judging from the new shroud I have in my house, is about

So, mathematically:

Radiator frontal area: 529 sq. in.
70% of 529= 370.3 sq. in.

Area of a circle= πR^2= 370.3
R^2= ~118
R= 10.86"
Diameter of properly-sized fan, according to Flex-A-Lite= 21.72"
Diameter of BMW fan= ~18.5"
Difference in area= 370.3 - 269.5 = 100.8 sq. in., or the BMW fan is about 27% smaller than Flex-A-Lite's formula says it should be. This makes sense, given that BMW added an auxiliary fan to compensate under high-heat conditions.

Now as far as current draw, I do not consider this an issue. The Zircon fans draw 10 amps, and as most of us with higher-mileage X's know, having a behemoth water-cooled alternator is more than up to the task of a few extra amps of draw.

[romeokc10]

Originally Posted by TriX5

Nope. My '06 4.8is only has the e-fan, not the aux fan. I have one of each, pre- and post face lift. The later car is quite different in many aspects.

Thanks, got it!

[papasmurf]

Originally Posted by gerry_miranda

My take...what ever you save in rotational energy...(remember its a fluid clutch and does not rotate one to one with engine rpm)...is taken back from you by increased alternator drag.

Still, an electric fan is much more efficient, and the amount of power it draws is less than what a clutch fan uses. On top of that, the alternator does make more power than needed, so it is not necessarily causing the engine to burn more fuel in that aspect.

Originally Posted by TriX5

Nope. My '06 4.8is only has the e-fan, not the aux fan. I have one of each, pre- and post face lift. The later car is quite different in many aspects.

Would you mind snapping a couple shots? I'd love to see how it is set up. Does the 4.8 e-fan run at all times?

Edit: Got a part number: RealOEM.com * BMW E53 X5 4.8is Fan shroud/fan

HO-LY CRAP! $550? Screw that, back to my original plan. Even with the discount I receive, it's still too much.

[JCL]

Originally Posted by papasmurf

Still, an electric fan is much more efficient, and the amount of power it draws is less than what a clutch fan uses. On top of that, the alternator does make more power than needed, so it is not necessarily causing the engine to burn more fuel in that aspect.

I don't agree that an electric fan is necessarily more efficient. It can be, but that depends on the control strategy, as well as how you measure that efficiency, as much as on whether it is electric driven or mechanically driven.

The first point is that with a mechanical fan, the parasitic load is related to engine speed, since the fan speed is proportional to engine speed. That is how you get more hp at the high end with an electric fan, by having a more constant load over a wider rpm range. Leave aside the fluid clutch for a moment. Mechanical fans have to be spec'd to provide enough airflow at idle in traffic, and that moves a lot of air at higher engine speeds. Flex (variable pitch) fans help here.

It isn't right to say that the alternator makes more power than needed. It makes exactly what is needed. It is capable of making more power than needed. This just isn't a free ride, though. If you put additional load on the electrical system, the alternator has to run more to charge the battery. At a specific steady engine speed, an electric fan can actually use more power than a mechanical fan. That is because both sytems have approximately the same losses in the belt drives, the fan themselves use the same hp in this example, but you have a direct drive (no additional losses) with the mechanical drive, again leaving aside the fan clutch, while you have a ~90% efficient alternator and a ~90% efficient electric motor, resulting in an 81% efficient drive system.

What you gain with an electric fan is packaging flexibility (which isn't important in a retrofit), as well as the ability to apply a more sophisticated control strategy. Without that control strategy, ie when just using a simple control, there isn't much to gain. You can gain top end hp by having the same parasitic loss at all engine speeds, but how much time do you spend at red line?

What you gain with a mechanical drive is the ability to move more air, particularly at higher engine speeds. If you are pulling air through multiple cores, that is important.

With both systems, fan shrouds and ducting can make very large differences in fan efficiency. That works against a retrofit, unless you can match the original engineering.

Lots to consider. I just wonder if the theoretical gains are worth it.

[Weasel]

/\ There he goes using logic again... I thought we warned him about that!

[TriX5]

I'll pull it out and snap a few pics this a.m. Never had a need to look at it closely but it seems like a clean install.

[Buzzcut]

So... my 2002 4.4i has that same electric fan shown in the Real OEM diagram. I know this because it has those same louvers.

Why would they use an electric fan and a mechanical fan? Does the electric fan only come on when the AC is on?

[papasmurf]

Originally Posted by Buzzcut

So... my 2002 4.4i has that same electric fan shown in the Real OEM diagram. I know this because it has those same louvers.

Why would they use an electric fan and a mechanical fan? Does the electric fan only come on when the AC is on?

Are you sure? The one that we are talking about is on the engine side of the radiator, not on the front.

[Zulu95]

A number on other makes board members use twin speed Ford Taurus electric fans which flow huge amounts of air and either DIY built control circuits or professionally built controllers.
These fans are used on V8 hot rods and some big engine rock crawlers and work very well. The OEM shroud is usually bought with th fan and then modified to fit in the other vehicle's OEM engine fan shroud. Total cost is usually south of $200 or so.
I am toying with the idea of retro-fitting our 4.7L V8 Toyota 4Runner and removing the engine driven clutched fan. (Similar to the BMW factory setup.) The toyota does not have the electric Aux fan used in our BMW's for some reason. I suspect it may be because the Toyota has a massive radiator up front.