right, so, while switching to an electric fan may reduce drag on the engine, it does not eliminate it altogether.

__________________
Paul
2004 E500 4matic; 72,000mi

A good designed fan motor will draw less amps, thereby not adding a hard load on the alternator. It will draw some amps, but the ponies required to make up for it should be less than the ponies needed to turn the clutch and fan assembly.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

test

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

There's a big piece missing here.

When you cruise down the highway with the mechanical fan, there is a fair bit of drag even if the fan clutch is disengaged. However, there is no additional load to the non-running electric fan.

When the fan is needed, there isn't much of a gain to the electric fan. The less you need the fan, the more gain there is.

A well designed electric fan's pull on the eletrical system should require less ponies to spin the alternator vs that amount of ponies needed to spin the fan and fan clutch.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

It takes a certain horsepower to move a specific amount of air.......dependent on the design of the fan, of course.

For two fans of similar design, the drag on the alternator to produce a specific amount of output for the electric fan will be identical to the drag on the water pump pulley to produce a specific amount of power for the clutch fan.

There's no free lunch.

As mentioned, the benefit of the electric fan is that it remains completely off unless needed.........the clutch fan takes some horsepower to spin, whether needed or not.

Depending on the type of clutch, there are other benefits as well.

Fans are typical turbo machines and they develop load measured in power (hp or kW) that rises with the cube of the speed. So, a fan drawing a tenth of a hp at idle, can be drawing up to ten hp at redline, if the fan is connected with a "no-slip" clutch. While a viscous clutch will begin to slip as the torque demand exceeds the clutch capacity.

It is rare that an engine is at full load while standing still, and the "not moving" scenario puts the highest priority on the fan's performance. This leads to a tough compromise in the blading design - they need to be very effective with the car at rest while they are almost superfluous at highway speeds. No clutch for a mechanical fan is likely to be able to achieve an optimum arrangement.

An electric fan changes the game. The fan blades are designed to provide the necessary flow to cool the water in the radiator with the car stopped in traffic on a hot day, or whatever condition is determined to be the thermally greatest challenge. As the car begins to move, the load on the fan is reduced, and, yes, the fan will draw less current. As the engine cools down, the fan can be shut off and be allowed to freewheel. At high loads, and higher speeds, the electric fan typically is not needed.

The electric fan offers the best fuel efficiency and thermal control options to date. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Only if the fan is off. If the fan is on, and moves the same amount of air, it will create MORE drag on the engine due to conversion inefficiencies from mechanical to electrical back to mechanical energy. Inspite of this, electric fans with proper thermostatic control work very well and are quite efficient.

__________________
'83 240D with 617.952 and 2.88
'01 VW Beetle TDI
'05 Jeep Liberty CRD
'89 Toyota 4x4, needs 2L-T
'78 280Z with L28ET - 12.86@110
Oil Burner Kartel #35

http://i16.photobucket.com/albums/b1...oD/bioclip.jpg

Actually, because the electric fan will run at essentially a constant speed, selected for the car not moving situation that becomes the most thermally challenging case, and the load gets lower as the car moves because the volume air the fan wants to move at its running speed requires less head, or pressure, to be developed by the fan (the resistance to flow through the radiator stays the same, but the car movement generates a higher than atmospheric pressure on the front side, which means the actual load on the fan drops), which at a fixed speed means lower torque or amperes are drawn by the motor.

The other issue with the shaft driven fan is, it has to speed up as the engine speed increases. Which means it draws more power from the engine when the engine needs it least of all. When you disable the clutch, and leave it constantly engaged, as is often the case with failed viscous clutch arrangements, you waste much more power at highway speeds or higher rpm. And there is a possiblility you can overstress the blades as they are not designed to spin at full rpm.

So, the electric fan very easily pays for itself in the energy consumption tally. Enough that I find the use of mechanically driven fans with those troublesome viscous clutches a bit like an anachronism. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)