I keep hearing that if you replace your clutch driven fan with an electric you get like 3 MPG better (sounds like wishful thinking) but it does make some sense as i hear that it take 30 or so HP to run the clutch fan.

Any thought and any one that has actually done it?

 

A few things, I have done it on two vehicles and you won't see more then 2mpg at the most. That said I wouldn't do it on a SD, especially a diesel, it is a lot more truck than a half ton or a car is to keep cool. I suppose if you plan to never tow with it then it could work out just fine. I also doubt it free's up 30hp as it barely had a seat of the pants improvement when I did it and 30hp would be very noticeable. The best thing about them is the increased AC efficiency in city driving you get plenty of air being pulled past the condenser when you are in stop and go traffic with the fans on, plus the small mileage increase is nice but you need to drive plenty for it to pay.

 

If it was a feasible system for a 3/4 ton or larger truck, they would be engineered that way.

 

Assuming it's the diesel you're talking about. The fan is clutched and variable. When it's commanded to 0%, it's using minimal HP, if any. When it's commanded to 100%, it's because the truck needs the enormous about of air flow that a 30hp fan can move. An electric fan just can't keep up.

 

I just don't see how this could save you any gas.

I look at it this way... to get the same cooling you will need the same size fan spinning at the same speed... With a mechanical fan you turn the mechanical energy from the fan belt directly into mechanical energy at the fan... there are minimal losses for friction etc...

Assuming you can find an electric fan that big, you have to first spin the alternator which has some significant effeciency losses, then you have to spin the electric fan and the fan motor has its own effeciency...

It sounds to me like you would loose mileage unless you undersize the fan which sounds like a bad idea to me.

EDIT: oh, and as far as gaining power... your alternator will increase resistance proportional to load. So if your alternator and fan motor are each 80% effecient and you loose 30hp with the mechanical fan, i would bet your alternator would drag about 30*1.2*1.2 = 43hp with an equivilant electric fan....

 

Gunnerdog - Yes that all sounds great and right along the line I was thinking with 2 set of losses. I did ask a friend of mine about this (hes an engineer at Freightliner - granted he dosent work with the cooling systems) but in theory it could work, smaller rotating mass with two small plastic fans and yes it does take more energy to spin the alternator at load but there is some energy still being used - Really I would just like to hear form some one that tried it.

 

We will see them from the factory - eventually. CAFE fuel standards are forcing automakers to consider and address all possibilities to improve MPG.

The challenge is, as mentioned, the amount of air that needs to be moved for these large engines. A fan with enough capacity will be expensive and draw a LOT of current - well over 100 amps, maybe 200? A much larger alternator (or two) will be required - along with heavier wires, relays, etc. I expect it will add $1K to $2K to the purchase price of an SD by the time all is said and done. Truck buyers are not (yet) ready to pay that to get the extra 0.5 to 1 mpg.

Some full size tractors have them already (saw one on a Volvo) so the technology is there. But for the most part, fuel is still too cheap in the US to get drivers to voluntarily switch.

 

You forget that E fans don't spin at all in most cases above 40mph, clutch fans spin all the time. There are always a few guys that over think it and swear the alternator is somehow spinning more than it already does because there is a Fan hooked up to the system. All I can say is I and many many others have gone to Efans on half tons and cars and get results pure and simple.

 

The challenge is getting enought CFM airflow to work. I have never seen a 12 blade electric fan yet.

 

I don't know about a 12 blade electric but this company has a good looking duel 8 blade

98-03 Ford Super Duty Diesel Electric Fan

 

The alternator doesn't spin more, it takes more power from the engine to turn it when there is an electric fan loading the alternator. It doesn't make electricity for free, it takes power from the engine.

That's very basic physics. You can't get something for nothing. If an electric fan runs it requires power, and the alternator supplies that power. The alternator takes power from the engine and converts that to electricity, with a loss due to inefficiency.

 

I know that electric fans have been looked into for some of the machines we (Cat) make and they haven't been feasible yet. I think they trouble they were having was finding fans that could move the air required and last as long as they needed them to. And this was on a Skid Steer with a 3.4L 4 cyl diesel. It does have the heat load from the hydraulics to deal with so it might be similar to a 7.3 engine.

Most of our machines run hydraulic fan systems since we can control the fan speed to match the cooling requirements and it doesn't require the engine to be inline with the radiator. Hydraulic fan systems are about 50% efficient. Or whatever power you need at the actual fan blade, it takes about twice that at the pump. They can get higher efficiency with different configurations, but that's a ball park. Most of the alternators I've seen are in the 60%-80% efficiency range. The newer ones are getting better. I'm not sure how the alternator on the older trucks are, but you would need to factor in the alternator efficiency as well as the fan motor efficiency to get fan shaft power to engine power ratio. Then the fan blades need to be compared to the original Ford fan to see if the same power gets you the same flow.

They keep tossing out 30hp for the stock fan, but with that clutch disengaged it seems to spin pretty freely. Perhaps if your fan clutch was toast and locked up, an electric setup would show a good improvement.

The other bonus for the electric fan is that you can get full flow at idle, which would help out the A/C, or help cool the engine off between drag races

 

On the show xtreme 4x4, They took a dodge and replaced the clutch fan with an electric one and picked up just over 1.1mpg no mention of hp.

 

I removed engine fan blades on my Mercedes diesel at the beginning at this summer and the highest temperature I have seen was still 40 degrees below the redline and that was while climbing Grapevine Grade -7 miles with average 5%, 82-85 mph, 83F outside and AC at full blast.
But the sedan has also booster electric fans for cooling while parked and in cars the 174 HP engine seldom use more than 25% of its power.
In my Powerstroke I can hear the fan coming on loudly. I make the point to drive with the speed that will keep the fan off most of the time for fuel saving. That said I can haul 17,000 total at 90F outside and at 60 mph the fan seldom comes in.
Talking about possible conversion.
NOBODY makes 30HP electric fans for the truck. End of the story.
Than in my JD tractor the fan has no clutch and runs at full engine speed all the time. I still can use tractor/backhoe for 2 days on 5 gallons of diesel.

 

Hmm, not the end of story and not quite! A 30hp DC motor(for the fan) would weigh over 100-150lbs! Probably more due to low voltage and high amps. Plenty of v8 cars seem to get by with a single e-fan. Granted thats a car and not a truck, but I cant see two 16" fans taking 30 electric hp off the alternator. 30 hp=22380watts at 13.5v it would draw 1658 amps! Not counting efficiencies of motor or alt.
Lets see, 2 fans, 25amp each (20-30 realistically, 25 average) is 2fans*25amp*13.5v=675watts of power. By the way, thats start power, running power is less
746 watts in 1hp. Both fans would draw less than 1hp. But,
Consider efficiency of the motors at 70%, thats about 1134.5 watts, just over 1.5hp.
Consider efficiency of the alt at a very rough 55-65%, lets say 60%, thats 1890 watts of power.
So, just over 2hp total.
My math is horrible and I welcome anyone to correct it. I have seen other web sites with completely different numbers, oh well.