Ok I used equations from fluid dynamics for a rough calculation about power used by a fan driven by the motor. I was hoping to get a big number thinking I could improve my truck. And its in metric because it easier to calculate and then converted to hp. Note all measurements are from my truck (2001 2.5) so your pulleys or fan may be sized differently.

Assumptions made (mostly to give myth best chance of being an improvement to truck)
-air temp at -10 degrees C so density is 1.3163 Kg/m^3
-fan is 100% efficient at moving air (usually around 70% realistic)
-air has no velocity before the fan
-pressure differential is ignored since open system (this part maybe what throws off calculation a little becuase it could have some effect)

Electric fan calculation.jpg

I also calculated fan at 50% lock-up at 2500rpm and it was .016hp or about 1/50 of a hp. One could argue that higher rpms would change result which it would, but if your driving over 2500 rpms I would argue your not driving for gas mileage and that was my main point for calculation on my part.

Also at 3500 rpm fan moves 1600 cfm (theoretical from my calcualtion at 100% effeciency) so if you want to size fan (depending on your driving, use of truck and same set-up of pulleys/fan) I would suggest 1 from 1500 to 2000 cfm unless you do alot of off-roading or towing.

I know there is more benefits such as quicker warm-up time and better control of temp, but for price and the likely-hood of not noticing anything I'm out of that mod for the time being.

Let the controversy begin!

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current - 2001 2.5 5spd 3.73 XLT reg cab short box 165K
dead - 2001 2.3 5spd 3.73 XLT reg cab short box 70K

Ughh math lol

What exactly was the point of this? Most people that upgrade to an electric fan do so so they have the option to override it, or they were just ugrading their cooling system as a whole.

Do your calculations consider the effect of the fan on engine acceleration or just at a constant engine speed?

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2010 Ranger Sport 4X4 4.0 SOHC Auto
Stock... for now.

no electric for me! I dont trust the electric motor. Id rather have a mechanical setup. So I installed a flex fan. Works great!

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Its for calculating the difference in power, which some say is enough to improve mpg. No, it does not take in effect for acceleration but you should consider it negligable since the interia induced from shape and weight of fan is almost nothing compared to that of all the other rotating mass (everthing on serp belt + camshaft + crankshaft + transmission gears + driveshaft + axles + wheels/tires, ect).

I did say there is other reasons for such modification at the end, but to claim saving $ on becuase of mpg improvement or gaining power would be false unless somebody can find a mistake in my calculation becuase the difference is so minute.

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current - 2001 2.5 5spd 3.73 XLT reg cab short box 165K
dead - 2001 2.3 5spd 3.73 XLT reg cab short box 70K

umm yeah... no

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I'm a little confused, are you trying find a relationship to equate the differents in efficiency between a engine driven fan vs. electric ?

If so you would have to start with a constant such as the fan size and weight, blade pitch and diameter.

Then you would have to take horsepower readings of the engine at the same RPMs as the fan motors max RPMs .

Then you have to convert the engines horsepower to Watts and calculate the electric motors amp draw to Watts.

There are so many variables such as temperature and humidity effecting air density ....

I think I just hyper extended my brain

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2011 Ranger XLT 2x4,4.0 SOHC, 5 Speed Auto, 3.55 Rear. Oxford White.

Simplicity is the ultimate sophistication.

Torque it down till it breaks off, then back it off 1/4 turn.

Math.......sucks...........fvck that.

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Cree Proverb

~Draw me not without reason, Sheath me not without honor~ 17th century swordmaker Gallegos

~1994 Ford Ranger 2.3L 4-Banger 217, 000+miles~

Sorry I should have explained better. I was going to look at power used by mechanical fan when electric fan would be off. So I looked at wasted power only. I used 2500 rpm becuase thats about where I cruise at. If numbers indicated that there could be even a hp or 2 drawn by fan when it is not needed, I was going to ask someone to use a timing light to tell me the rpm of fan during slippage, which I found to be unneeded.

So max wasted power (clutch not slipping at 2500rpm) = 1/8 hp
at 50% lock-up = 1/50 hp

And about equating power drawn during both fans engaged, that would be out of my realm becuase there is too may efficiencies to account for.

And come on guys math sucks, but in applied applications (engineering) makes it interesting doesn't it?

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current - 2001 2.5 5spd 3.73 XLT reg cab short box 165K
dead - 2001 2.3 5spd 3.73 XLT reg cab short box 70K

I have a Bachelors degree in math and I'm a math teacher so I'm offended

Just kidding

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I have an electric fan on my truck and the one thing you did not take into account. The electric fan is only on when its needed.

For example, this December and January, I don't think the fan had to turn on once. OK maybe once.

The mechanical fan clutch always uses some engine power regardless of temp, yes a lot less when cold and more when hot, but the fan always spins

And I agree, math is worthless unless it can be used in the real world.

math for the fuggin win!

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1999 xlt 2.5l 5-speed Supercab 159k
83 diesel 2.2l na
06 F250 6.0l psd
{click for lol}

Okay guys. We need a controll ranger to dyno with a mechanical fan and then dyno the same truck under the same condtions with an eletrical fan. Now...whos gonna do it?

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Patrick Poston 1990 ford ranger 4cyl 5spd 4wd & 1984 ford ranger 2.0 4spd 2wd. Love em' both

No, that is exactly what I did. I am saying that a mechanical fan is using 1/8 hp at 100% fan speed and 1/50 hp at 50% lock-up which is wasted power under conditions that don't require fan to cool engine, since electric fan does not run under those conditions that is the power you would save.

Again I am saying the difference in power is when mechanical fan is spinning and the electric fan would OFF. Which by my calculation is a max of 1/8 hp at 2500 rpm. (This is for my specifications, your truck may be different a require different #s to be plugged in.)

And yes a dyno would be neat, but I bet most people reading this thread are cheap becuase they are interested in the possibility of saving on mpg. I am not saying there isn't other benefits but I am saying I doubt improvement in mpg or noticable power can be expected.

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current - 2001 2.5 5spd 3.73 XLT reg cab short box 165K
dead - 2001 2.3 5spd 3.73 XLT reg cab short box 70K

I think adding a pressure rise across the fan will add quite a bit to the power required but at any rate making an approximate calculation without any measurements is hard because the power is very sensitive to pressure and fan speed both of which vary a bunch on the front of an engine. Anyway here's my swag...
Assuming 1/2 hp of average power draw
13 hrs run time per tank (that's 400 miles at average of 30 mph)
BSFC 0.5 lb/hp-hr
equals 0.53 gallons per tank or 0.53/20=2.6 % of gas per tank used to power the fan. Not a ton but if you can save most of that you would be doing better than just about any other simple engine mod.

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1996 4X4 Super cab
4.0 5 speed 3.27 gear

ok. lets talk electric fans.

I run an upgraded battery first off, so the draw to my alternator is very low as my battery will start a semi.

I run a topaz fan. it runs at 15 amps. its load on the system is so low my headlights dont even dim when it comes on. I gained throttle responce off the line as it doesnt have extra load to spin up. Im also saving my costs of waterpump replacement, being that the fan is extra weight and load on your water pump bearings. (35" tires on stock wheel bearings do the same thing)

So im saving money on parts, and gaining throttle responce. what else?

well in -10C weather, it doesnt turn on. it wont run till my truck hits near 200C. Know what that means? My truck warms up faster as i dont have a fan pulling 1500cfm of air over already cold coolant, cooling it further. This gets my truck to temp fatser, again saving gas by taking it out of "choke" mode where you burn more gas then normal.

No what else have i gained? Well my E-fan saved my truck a few HP, as that fan does take up more then .016 of a hp to turn.

My AC blows colder now that it can run when my ac pump is on, my truck is quiet, and best of all i can shut it off when i dont want it running (deep water).



Now as for reliability, lets do a comparison. i work at ford. ford hasnt used a clutch fan since the ranger, and has been electric for 5+ years on their fleet of vehicles. Whats that tell you? It tells me that a sealed electric motor is just fine to use in a vehicle application.

ive been running a 93 topaz fan for 2 years now, its old, rusty, beat up, and has been under water many times.

IT still works great!


Actually install an e-fan properly, and youll never go back. theres a reason that nothing made today has a clutch fan.

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