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Old 01-20-2008, 07:05 AM   #1
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Electric fan vs. Belt-driven fan

I just had a thought and was wondering if any of you could help shed some light on it for me. I am using a friend's '96 Dakota 4x4 with the 5.2L(318ci)V-8. I am getting around 13MPG right now. The thought I had deals with the belt driven radiator fan. I had a friend that replaced his belt-driven fan in order to reduce parasitic loss and gain some power. I would think that this decrease in parasitic loss would result in a little more fuel efficiency. Any thoughts?


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Old 01-20-2008, 07:17 AM   #2
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It would definately provide a slight increase in efficiency, but it's not likely to be noticeable. You'll likely save more fuel by simply shifting it into neutral at every stop.


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Old 01-20-2008, 07:30 AM   #3
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If the existing fan clutch is working properly switching to electric will not make a noticeable difference. I've tried it and went back to the fan clutch for its simplicity and ability to cool when towing.
You would get better results just keeping your tires inflated.
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Old 01-20-2008, 08:49 AM   #4
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clutch or not, the mechanically driven fan still spins, albiet at slower speeds when not needed. An electric fan will only run when it is needed. Warm up times with an electric vs mechanical fan can be quicker in the winter time because the fan is not running when it is not needed.
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Old 01-20-2008, 12:50 PM   #5
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the problem with a mechanical fan, clutch or not, is that every time you change RPM it's more rotating inertia to overcome. this is, of course, all going to be relevant to what kind of driving you do (very little if any difference on the highway), engine, and vehicle. a 5.7l v8 probly won't notice it much at all but a RWD 4 banger probably will very much so. I wouldn't count on it being a night/day difference but it may show itself over time in a few % gain in FE
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Old 01-21-2008, 04:31 AM   #6
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There are posts above indicating that other things will give you more benefit than you'd get from the e-fan. Probably true.

However you should do those other things anyway. You don't have to make a choice between tire pressure and an e-fan. Same for neutral idling instead of in Drive.

Generally you'll get FE improvement by making a bunch of changes. Some are easier than others. It's the combined effect that will add up to something.

The e-fan was the first FE mod I did on my car. I have to admit I haven't been able to document that it's helped with fuel economy. The car is pre-'86 so no ScanGauge and also, switching fans is a bit of a pain so doing a comparison test would be a challenge. However, all told, the car is doing well as far as FE goes.

In my case I wouldn't change it back. The car is a bit underpowered by most standards so anything I can do to "unload" the engine is helpful. If you do put one in, I highly recommend an LED on the dash to let you know when it's running. I can't hear mine come on even when idling at a stop so the LED is the only thing letting me know it's working as expected. I definitely want to know the fan's working!
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

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Old 01-21-2008, 07:48 AM   #7
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I've gone from a mechanical fan to an electric fan before and if your fan clutch is in good condition I think you'll like the difference in mileage. I personally will never swap out a mechanical fan again.

I realize that on the freeway most cars don't need a fan pulling air and a perfect mechanical fan or a true 'clutch' fan wouldn't be. But, it does, always. Only a mechanical fan with a badly worn clutch will you not see much of a gain, if any, by swapping out. A good mechanical fan clutch will get fairly stiff at idle. It'll take a good 10-20 seconds to loosen up after you take off from the stop. On the freeway the radiator will warm the clutch and it will be pulling air, more air than the radiator will flow on it's own. In my old car that got converted to electric fan, anything above 90 for extended periods even with the electric fan on it'd start to heat up. This is in a car that would ran regularly 110-120mph for 2-3 hours straight no problem before the conversion.

A typical stock mechanical fan flows a maximum 10,000-11,000 cfm and typical electric fans flow a max of about 3,000-3,500cfm. This is important because the less air you move the less energy, however, electric fans are nowhere near as efficient as mechanical fans at moving the same amount of air since you have to convert mechanical to electrical then back to mechanical and that has losses.

There are some plusses but also negatives. It's up to you as to what you want to do. I'm sure if you are going for FE it'd be best to do away with it. If the truck does any actual work I wouldn't recommend it.
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Old 01-21-2008, 09:03 PM   #8
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on my s-10 (has a 4 banger) i noticed a 1-2 MPG increase when i went from clutch fan to electric fan, heater got warmer quicker, fans never on at highway speeds, maintains cooling even on the hottest days and while towing.

id love to do it to my chevette (non cluch fan, bolted straight to the pulley) because obviously with that small of an engine i need all the oomph i can get (frees up some torque) an dwhen torque is freed up and not wasted in a fan at cruising speeds then thats more torque available to go to the wheels thus less gas needed to do the same ammount of work
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Old 01-22-2008, 04:04 AM   #9
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I had two chevettes, a 1980 Scooter that had an auto that slipped between 1st and 2nd upshift, and then later a 1981 4 dr with a 4 speed. Those cars could take a beating.
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Old 01-22-2008, 05:16 AM   #10
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The fan in my Saturn has not worked for the last 8 months. You really don't need it, as long as the car is moving.

BTW a mechanical fan doesn't draw as power as people might think, because if the car is moving forward at 35MPH and the fan is trying to pull air at 35 MPH it works out to nearly zero.

On the other hand, it's nice to get rid of some weight on the water pump bearing, in my experience the water pump's life will about double.


Think you are saving gas? Prove it by starting a Gas Log, then conduct a proper experiment.
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