I've got a pair of 2 speed fans installed on my truck for less then $100 total. The first fan comes on with the ignition, the second fan is on a temp switch and comes on at 210 degree water temp and the the high setting on both fans are on a switches so I can turn them on from the cab.

Far better then the factory fan. Much quieter, frees up a few HP and has a higher CFM then the factory fan.

 

I have heard this a lot about people and electric fans, but an electric fan is unable to keep up with towing heavy loads. You may think that the factory fan doesn't flow much, but an electric fan just can't flow what the factory fan can. If your not towing heavy you will be fine it will free up some hp and get some mileage gain.

 

If your talking about the flex a lite fans, you are absolutely right. The fans I have mounted move 1 1/2 times the CFM's of the stock fan if I have them both running on high. Through hay season I am pulling 20,000 pounds plus at low speeds through the river bottoms in 90 plus degree days with high humidity. I even run the air conditioning and these are hilly roads that I'm in 2nd gear pullin it up.

So far I have never had to turn both fans on high yet to keep the temps down to normal. Only had a few occasions of turning one fan on high.


Here's a good thread on the subject. It's about 12V but everything is the same for our trucks. https://www.dieselbombers.com/5-9l-r...-write-up.html

 

How about some pics and details...??

 

I can get some pics tomorrow and get em up.

 

whats the cfm of the stock fan? so your running 2 3800 cfm fans then right?

 

Been a while since I looked all this up but I think it was 6000cfm at idle. Once your at about 20mph the fans are doing very little to add to the cooling affect with the air flow through the radiator.

Pics are on hold for the day, been a wet nasty day here today so far. Hopefully tomorrow.

 

The Myth Of The Electric Fan

What's important to note is that the fan is only used when the engine is idling, or the car is creeping along at low speed (less then 20 MPH). If the car is stationary or creeping, there is not enough natural airflow through the rad to provide adequate cooling. Thus, the necessity of a fan.

Now that we know the basic operation of the cooling system and fan, let's look at the electric fan.

By far, the most common misconception is that the electric fan cools better then the stock. People see the high CFM numbers in the catalogues (for example, the Black Magic is advertised as pulling 2,800 CFM, and the Perma Cool "finger chopper" is advertised at 2,950 CFM) and are impressed. The truth is that no one actually knows the CFM rating of the stock fan. It has simply never been measured by anyone but Mazda. Some estimations have been made that it is approximately 2900 CFM at 2600 RPM using software modeling. But as these are estimates we can never know for certain how Mazda has rated this fan. All we do know is that it is rated at "enough". And to be honest, who cares how much air the stock fan moves? It is more then adequate as long as it's clutch and the rest of the cooling system is in good shape. The steeply raked blades of the stock fan move quite a lot of air, even if it turns slower then an aftermarket electric unit. It's also a bit irrelevant how much capacity the stock fan has as compared to aftermarket fans on a modified car because the fan is only used during idle and light-load situations. The fan to cool a 400HP engine is the same size fan as would be used to cool a 200HP engine since both engines are producing the same amount of heat during idle and light cruising.

Many people also seem to believe that an electric fan will cure their "at speed" overheating problems. Recall that the fan is not even used when at speed, as the natural flow of the of air through the radiator is more then enough (much more then a fan, in fact) to keep the car cool.

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Of course, you're not necessarily after better cooling. You've seen those TV commercials or catalogue ads that promise "Up to 17 free HP!" by converting to an electric fan. Well, that's simply not true. There will be a horsepower gain for sure, on the order of 0.5 - 1HP. But remember that the electric power to run the fan must come from somewhere, and that somewhere is the alternator. Electric fans draw quite a lot of current. Most pull surges of 35A or more to start up, then run at 8A-10A. This puts extra load on the alternator. Ever pedaled a bicycle with a generator powered light? If so, then you will know that as the electrical load on a generator/alternator increases, the generator/alternator becomes harder to turn. Suddenly, all that "free" HP you just freed up is once again being used. This time, though, it is being used to turn the alternator. There is also an inefficiency in the whole system. We are converting mechanical energy, to electrical energy, to mechanical again to run the fan. This very inefficient, much less then just driving the fan directly via the mechanical energy of the rotating shaft.

Let's examine the "17 HP!" claim a little further to drive the point home. A little basic math is all that's needed.

One horsepower is 745.69 watts.
Therefore, 17HP = 12,676.89W.
Since W = Voltage * Current, 12,676.89W is 1056 Amps

So in order to do the same work as that stock "17HP" fan, an electric fan would have to continuously draw over 1000 A from the electrical system of the car. Clearly this does not happen. Now I'm sure that somewhere out there is a car or truck with a ridiculously inefficient and so poorly designed stock fan that it actually does rob 17HP from the engine as it turns. But since the RX-7 comes with a well designed freewheeling clutch fan as already explained, the RX-7 is certainly not that car.

As for the pic my fans work great (Flex-a-lite) RATED for 18,000 pounds,have towed more then that.Maybe the engineers have not incorporated that a cam,ported head,intake and bigger turbo or compounds with bigger injectors will more more air and heat up and cool down much quicker then stock.

 

It seems many, many vehicles of every type and size have a variable fan. Whether it be RPM, clutch, or electrically controlled. Agreed that the majority of cooling comes from the vehicles speed and the air entering the radiator. BUT, why is there a speed change in fans while the vehicle is running down the road? Granted that IF you could go fast enough you would never need a speed change in your fan, but there is. I guess the rad just ain't big enough!

I'm not going to argue the numbers, ideas, and preferences, but I will say this.
I want electric cooling fans for 2 main reasons.
1) Quicker engine warm up in cool temperatures, get to -40 around here.
2) They can cycle, or be on steady, with the A/C clutch. I know my A/C work a lot more efficient when I am rolling down the hiway, due to more air flow. But around town, or stopped it kind of sucks. Something electric fans would cure.

I don't do a lot of towing, but I guess that shouldn't matter as once the rig is going down the hiway, I don't need a fan. Correct?

 

I held out talkin about these fans for a while so that I could test them before I encouraged anybody else to make the change. I ran em all summer on this old farm truck. City, highway, empty, loaded heavy in high heat and cold weather and so far I have no negatives to share.

I still can't speak for longevity as far as service life but I don't see this being an issue. Past that, no matter what argument can be presented, I have tried and tested these things and they work.

This is what we did. Hard to show much with the lack of space to get a camera in there.