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  #161  
Old 07-01-2015, 12:41 PM
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Quote:
Originally Posted by PropellerHead View Post
That's impossible.

Signed,

Trader4
Are you joking or serious?
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  #162  
Old 07-01-2015, 01:13 PM
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Quote:
Originally Posted by DSSA View Post
An interesting read on parasitic loss from mechanical fans:

Dyno testing on fans, alternators and oil.....all here!

A couple of issues to note if reading it:

1) The fan/clutch systems on the older Chevy Smallblock is going to be quite a bit larger/heavier than on the X5s.

2) Fan draw on a stationary dyno will differ than while driving (be larger) due to frontal flow in proportion to the speed you're traveling.

However, it gives a little insight on the subject with measured data.

I personally wouldn't remove my mechanical fan simply for the sake of performance gains on something like the X5, however, the other aspects like being able to have control over what temperature it starts/stops, being less of a PITA to work on the car, etc. is why I would switch it over like my E39 and Wrangler should the motivation/opportunity arise.

I wouldn't suggest it be a "go to" modification, but like all modifications to a car, whether it is worth it or not depends on your own desires/needs.
Interesting document, good addition. More info--an electric fan runs at a constant CFM and other type fans do not. The same contribution to cooling is realized at an idle and max RPMs. That assumes the fan is running at all at higher RPMa when significant air is forced into the radiator. Because of the CFM at idle the fan shuts off some of the time. If racing the controller can be adjusted so that the electric doesn't run at all and for a short period of time the aux fan will not either.

Using a clutch fan as an example. It is always turning. Even when the radiator heat is not locking the thermal control the fan increases load as RPMs increase. The load is increased at all RPMs if the thermal control is locking which causes the clutch fan to move entirely based on engine RPMs.

FYI-I would like to add an electric water pump for the same benefits. I haven't looked but my bet is there is not one available.
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  #163  
Old 07-01-2015, 03:30 PM
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Quote:
Originally Posted by bcredliner View Post
Are you joking or serious?
I was giving Trader a hard time. Joking.
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  #164  
Old 07-01-2015, 04:10 PM
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Quote:
Originally Posted by trader4 View Post
Then someone should be able to explain the physics of why this
little 15" fan can require so much power to operate where all
similar size fans, doing similar work, don't require anywhere near
that much power. What is so special?

Also note that a dyno test is without the car moving. With
the car moving air is being rammed into the fan, which would
substantially reduce the power needed. At highway speed there
is enough air that the fan probably isn't needed at all. And
was the test done with the electric fan running or off?
Dyno was done with the fan off of course. Leaving it on creates a fairly large load on the alternator and will cause HP loss. That's one of the points of going with an electric over a parasitic. You don't have to run it all the time... as you said like at highway speeds and such. Less wear and tear on the water pump snout/bearing is a nice bonus as well.

The comparisons you are trying to make with other application type fans are not going to work... and I wish I were a mechanical engineer to explain technically why. But trying to compare say a 5hp fan with a dedicated 5hp engine on it to a 120hp car engine with a fan on the front of it is just not an apples to apples comparison. Rotational mass, condition of fan clutch, etc, etc... will all come into play.

bcredliner... I believe there is an electric water pump available for the M54. At least I THINK I remember reading something about them on e46fanatics.
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  #165  
Old 07-01-2015, 04:20 PM
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General question on all BMW models...
Does anyone know which year BMW stopped using mechanical fan clutch (and went electric)?
Is it around 2009 on F10 models etc.?
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  #166  
Old 07-01-2015, 04:38 PM
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I think it was generally after the M54 engine. Even some of those were electric... e46 coupes for example.
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  #167  
Old 07-01-2015, 05:31 PM
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Quote:
Originally Posted by cn90 View Post
General question on all BMW models...
Does anyone know which year BMW stopped using mechanical fan clutch (and went electric)?
Is it around 2009 on F10 models etc.?
Well, we know the 2004 4.8is is electric. That would probably include the early 545i E60's from late 2003 as well.

The electric fan in an E46 included any manual transmission starting in 1999.
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  #168  
Old 07-01-2015, 11:47 PM
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Quote:
Originally Posted by trader4 View Post
Then someone should be able to explain the physics of why this
little 15" fan can require so much power to operate where all
similar size fans, doing similar work, don't require anywhere near
that much power. What is so special?

For example, an attic fan is fractional hp, 1/10hp. A central
AC condenser fan for a house that moves a huge amount of air
is 1/4 to 1/3. It's a very similar application, it's pulling air
through a radiator scheme. A furnace blower fan that moves
2000 cfm is 1/3 or 1/2hp. And I also showed where a 10hp
fan moves 66,000 cfm with a 5 ft blade. How do you reconcile
that with an auto fan?

Also note that a dyno test is without the car moving. With
the car moving air is being rammed into the fan, which would
substantially reduce the power needed. At highway speed there
is enough air that the fan probably isn't needed at all. And
was the test done with the electric fan running or off?
It boils down to aerodynamic drag. As with increasing a vehicle's speed, it takes four times the power to double the speed. So if the engine fan is consuming 1 horsepower at 750 rpm, it requires 4 horsepower to spin it at 1500 rpm, and 16 horsepower at 3000 rpm. Moving air through the louvered fins of the AC condensor and radiator which are designed to create turbulence in the core for improved heat transfer, then push that air out of the engine compartment, requires a lot more power than moving air with a room fan or attic fan.

Electric fans are able to meet cooling requirements becaue they tend to move more air at lower vehicle speeds than the engine fan and because radiators now use aluminum cores for better heat transfer. As the vehicle's speed increases, enough air is forced through the radiator to cool the engine generally, although the electric fan will kick in for additional support under high engine operating temperatures or when the AC compressor is running.

Attic fans, room fans and ceiling fans move high volumes of air because of their blade area. As a result, they don't need to run at high rpms and thus don't have the same power requirements. And I don't think any of us would want a 50 inch tall radiator core.

As a side note, my 1981 Bonneville diesel was equipped with the heavy duty police cooling option which consisted of a steeper pitched fan, heavy duty locking fan clutch, and double belt drive pulley. When the fan clutch engaged, it felt like it could suck a small car right through the grille, but it would knock 20 degrees off the temperature guage in less than two minutes. When it comes to automobile cooling, it's all about air velocity vs radiator frontal area.

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Last edited by srmmmm; 07-02-2015 at 10:19 AM. Reason: Corrected HP at 750rpm & 3000rpm. Power goes up by the square as air velocity doubles.
  #169  
Old 07-02-2015, 09:33 AM
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lol you guys.

Thanks for the fun reading.
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  #170  
Old 07-02-2015, 10:32 AM
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Quote:
Originally Posted by trader4 View Post
The power required actually goes up as the cube of the speed.
Power is squared as speed doubles. I've corrected the horsepower figures in my original response. Too much late night calculation effort involved. They should have been:

750 rpm - 1 horsepower
1500 rpm - 4 horsepower
3000 rpm - 16 horsepower

Now does an automobile engine fan ever really pull 16 horsepower? Probably not because the viscous drive clutches never fully "lockup". There is always some slippage which limits the top rpm of the fan blade itself. If it's a pure mechanical fan, bolted straight to the drive pulley, then the blades will flex, reducing the horsepower needed to spin the higher rpms.

You're correct on the stationary dyno situation emphasizing the fan load, but going to the electric fans was a major fuel mileage contributor when we brought out the "X" cars (Chevy Citation, Pontiac Phoenix) in 1980 at GM.

2002 X5 3.0 281,400 miles
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