Electric Fans for engine cooling

Folks,

I'm thinking of installing electric fans on my 2005 F-250 SD V-10.  I know that factory fans take 6-8 raw HP off the engine, and are a HP drain, even with the clutches that "free-wheel" and blades that flatten when traveling down the road.  6 HP would add 3-4 MPG, but I know there's no free lunch, the cost of running the alternator at higher output, as an example.

So, anyone know how or where to get the air flow required data?  I know the fans need to run when the AC is on, but can they turn off when going down the road, say be tied into an air-flow switch?

Any general thoughts here, lots of experience on this forum.

johncmr

"Any general thoughts here, lots of experience on this forum."

I wouldn't do it. Mechanical fans give a lot more cooling than electric. That's why they still use mechanical in trucks & vans, RV's and heavier rigs. They push a lot more air.

Personally I have more faith in the design engineers and feel if electric fans would perform better thats what would have been installed at manufacture.

My Winnebago has 2 large electric fans in front of the radiator. I wonder if they were wrong to do so, Ron. I assume they have engineers on staff.

  They only work periodically at highway speeds.

carson FL

I am not saying electric fans are not any good Carson but that is likely the engineers would use them if the application would benefit.  In your case obviously the engineers felt the electric fans were the best choice.

You said the belt driven fans suck six to 8 HP

Oh let's see what we would have to do to move the SAME amount of air electrically

We would need, six to 8 HP of fans.. Let's use six

Ok now motors are only about 75% efficient so that means we need 8,000 watts of electricity  That's about 10 HP by the way

Now generating electricity is only about 75% efficient, so now we are up to 12 HP to make 8,000 watts to push the same amount of air we pushed with an 8hp fan or 50% more power lost

So a belt driven fan simply uses less power per cubic foot of air moved.

NOTE that "About 75%... Thomas Edison optimized electric motors back in Menlo Park.. And there has not been much in the way of improvement since.

300 HP V10 add 6 HP = 4 MPG increase! I believe it , I do 

Interesting comments.

Let's take a stab at a few, 

About 1/2 of the transit buses in the world use electric fans, so the size of the engine or vehicle for mechanical fans or electric is possible.  All railroad locomotives are electric fan cooled, even the 4,500 HP GE's, and the 5,000 HP EMD's.

Automotive engineers are currently using electric fans in a large number of vehicles, some fairly high HP, my Caddy STS with the big Northstar engine has electric.  Many smaller cars are too, especially since the transverse mounted engines.  The 1989 Caviler I had was electric.  I drove a Segrave firetruck for years, electric fan (when it went off it really moved some air!).

The 6 to 8 hp is a number from Summit racing, and they got it from a dyno, a fan moving lots of air is about the same as the AC.  Could be wrong, but they don't seem to have a dog in the electric fan race.

The biggest electric fan available (2 of which, side by side used in the bus market, cooling a Detroit V 871) moves 4,500 cfm and has a suggested fuse of 20 amps.  Volts x Amp= Watts or 240 watts

There are controllers for electric fans which slow the fan relative to the temperature of the cooling water, and have a manual over-ride, and turn the fan on with the AC.  General idea is to save the fan and electricity.

The efficiency of an electric motor moving air is relative to the amount of air being moved, so when going down the road, the ram air effect will lower the current in the fan circuit (don't think so?  Put your hand over a vacuum cleaner hose and note the motor speed up, no air moving, no work being done, less load [amps] on the motor).

So, with this in mind, let's continue the discussion.

Johncmr

I am in the camp that believes electric fans to be a plus. Most of the manufacturers that use them in front-drive vehicles, do so because they cannot get the mechanical fan  to the front. Buses for the same reason (mostly). Plus buses tend to idle a lot and an electric keeps consistent. Most vehicles that incorporate both mechanical and electric have the electric controlled by a temperature switch. The switch is usually 5 - 10 degrees F over normal operating temperature. You could do the same with a temp switch. Yo could also have an override switch (hand / auto) inside so that you could put the fan on in anticipation of a hill or when approaching stopped or slowed traffic. I would not eliminate the mechanical fan. But there are more efficient blade designs, so you could replace it. If you put the electric you could even get an under-drive pulley for the mechanical fan. That way you would "cancel-out" some of the extra load of generating current. Don't know if you have an oil cooler and an auxiliary transmission cooler. If not (and the engine is working hard enough to warrant a fan) then install those also. Especially the trans cooler. when you look them up on the web, there should be specs as to current draw etc. I don't buy the 8K of watts at 12V. That would be 80K at 110 (roughly). I chose one at random on the Summit site:  http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-G4852&N=700+115&autoview=sku It has a 22 amp draw (264 watts) . This one has 7.9 amp draw (95 watts):  http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-G4903&N=700+115&autoview=sku Here is a 4,000 cfm fan http://store.summitracing.com/partdetail.asp?autofilter=1&part=DER-16928&N=700+115&autoview=sku 50 amps (600 watts) For the first and last, you need at least a 130 amp alternator..... 160 would be better.

Oh yeah, forgot to mention. If you did eliminate the mechanical, the electric HAS to go on the engine side of the radiator. Besides pulling air through the radiator, the fan directly blows air over the engine. If the fan is on the grille side of the radiator the air would much too diffused to be effective in cooling the engine compartment.

I installed a Dual type, Flex-a-lite fan on my 1989 Full Sized Bronco, about 4 years ago...I was replacing the engine and decided to add the elec Fan along with the new radiator, while I had lots of room to work...couldn't be happier with the results!

Here's the one I installed:  http://www.flex-a-lite.com/auto/html/27inch-electric.html

I also upgraded the alternator at the same time, as I do some towing.

Electric fans give you consistent cooling at most all engine speeds - especially if you're stuck in an idling situation in hot weather, when a mechanical fan would be turning at a lower speed...this is really important if you use your AC a lot in these situations... incidentally, the fans are wired so that when you turn on your AC, it runs the fan at full speed to give you the best possible air flow across the condenser to keep the AC performing at it's best...another big PLUS, in my book.

I don't really buy the 'increase in MPG' claims, I might get a fraction better milage, but not something you can measure on a consistent basis...Maybe in cold weather, as the fan will run slower, or not at all, when a mechanical still runs slowly, even if the clutch tries to shut it down...MPG savings may pay back the expense of the fans over their life, so it's probably a toss up, in that regard, IMHO.

Unbolting the mechanical might also allow the water pump bearings to last a bit longer, due to less strain on the shaft...IMHO.

Elec fans also provide a 'cool down' feature as they continue to run for a limited time after you shut down your engine - blowing air over the hot engine till the thermostat shuts down the fan...use the largest cold cranking amp battery for your particular vehicle - don't skimp here!

My Temp gauge pretty much stays right on the same spot, winter or summer, hot or cold...the thermostat in the fan control slows down or shuts off the fan when it's not needed, and in hot weather it runs the dual fans, full blast, unless there is lots of ram air from high speeds.

All-in-all, I think they are a good idea, providing you get a unit mated to your radiator/engine combination...don't buy a 'cheapie' or try to get by with an undersized unit...I'm looking into installing one on the Excursion with the V-10, if I can find the right unit.

Ram air on your fan going down the road will try to spin your fan backwards and will most likely increase its amperage draw. If this works out for you and you save 3-4 MPG after installing a fan please let us know, I may install four of them and pick up 12-16 MPG!

carson said:

My Winnebago has 2 large electric fans in front of the radiator. I wonder if they were wrong to do so, Ron. I assume they have engineers on staff.

   They only work periodically at highway speeds.

carson FL

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Those two fans are for the AC condenser cooling but provide auxiliary cooling for the engine as well. There is also a temperature operated fan behind the radiator. You can usually hear it engage because of the noise.
My electric fans run a lot of the time. They are triggered by either engine temperature or a set pressure in the AC system. My mechanical fan doesn't run very often - usually only in hot weather or going up hills.

Ram air on your fan going down the road will try to spin your fan backwards and will most likely increase its amperage draw.

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Wouldn't ram air go in the same direction as the fan is trying to pull it (from the front of the radiator to the back)?  If so, it will try to spin the fan in the SAME direction and reduce it's current draw, not add to it.

Yes, Ram air would reduce amps, if fans are off, hopefully they would not work as generators and slow the air.

Correction, the fan I mentioned above was for a 24 volt system, so my wattage is low, should be about 500 watts. 

regularguy, the F-250 SD comes with an aux oil and tranny cooler, but good points. 

I will need to check the alternator output, but I think I'm ok there.  The trailer has LED lights, so little load there, just brakes and minor battery charging.

I think I'll try it, document the changes and let you know.

(Gonna save all the old parts though!!)

johncmr

OOP's I was thinking backwards yes ram air same direction! No rotation at all less drag, one of first things you do as a pilot when your cooling fan stops is slow your air speed to stop wind milling of cooling fan to reduce aerodynamic drag!

Ron said:

I am not saying electric fans are not any good Carson but that is likely the engineers would use them if the application would benefit.  In your case obviously the engineers felt the electric fans were the best choice.

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I am an engineer and I can say conclusively that just because something works better does not mean it's chosen.  Cost (of both the fan and the installation/other factors) often has the largest say in what's done.  So while a mechanical fan may be included in your rig, an electric may do the job better.  Just have to spend the bucks.

I would also question the 3-4 MPG on a 6HP gain.    If that were the case, the price of a K&N filter would be approaching it's wieght in gold...  ;D

"I would also question the 3-4 MPG on a 6HP gain. "

I question  if there would be any noticeable difference at all, even if it looks better on paper.