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How to Choose an Electric Fan

2010 April 24
by admin

Whether we're at events or on the tech line, how to choose an electric fan is one of the questions we answer very, very frequently. While Flex-a-lite offers electric fans designed to bolt right into quite a few factory applications, we'd like to take this opportunity to help guide you in measuring your car of 4x4 to fit it for an electric fan.

The first step is to make sure you want an electric fan. Click here to read our article on electric versus belt-driven fans for more information on that topic.

To choose your electric fan, we recommend that you determine the minimum airflow you'll need, because you'll want to rule out fans that won't cool your vehicle. Consider the following minimum cubic feet per minute (CFM) ratings for basic engines:

  • 1,250 CFM for a 4-cylinder
  • 2,000 CFM for a 6-cylinder
  • 2,500 CFM for a 8-cylinder

A further note is that engines that are 5.0-liter (302 cubic inches) or larger should use an electric fan with 2,800 or more CFM. Obviously, an 800-horsepower engine will need more cooling than a 400-horsepower version regardless of the cylinder-count, but this basic guidance will get you started. And no amount of CFM will keep an engine cool if the radiator is under-sized or if too much of the grille-opening is obstructed. But let's move on, assuming that you have a typical engine in a typical enthusiast's car or 4x4 with a proper radiator.

Now that you know the minimum CFM required, you need to determine what will physically fit. This is easiest to do if you remove the belt-driven fan and fan shroud so that you can accurately measure the radiator and the distance between the radiator and engine components. Measure the radiator core; the finned surface between the two tanks. Watch this video for step-by-step instructions.

You'll want to select one of our fans that covers as much of this space as possible. In many cases, you may be better off with a dual fan because the shroud will pull air through a larger area of radiator than a single fan. Next, measure the distance between the radiator core and the closest engine component.

A few rules of thumb that we'll pass along from our experience:

  • Don't use an electric fan as the primary fan on 4-core radiators. It overworks the fan to try to draw air through these extremely restrictive radiators.
  • It's recommended to have at least 70-percent of the radiator core covered by the fan shroud.
  • Use puller electric fans (mounted behind the radiator) for primary cooling. A pusher (mounted in front of the radiator) is appropriate as an auxiliary fan.

These general guidelines should address most of the questions and issues you run into when trying to determine which electric fan will fit on your application.

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14 thoughts on “How to Choose an Electric Fan”

  • Chad
    Chad April 24, 2010 at 4:55 am

    Very helpful. I like the video that helps clarify exactly where to measure. It have been nice to see the install of the electric fan as well.

  • 5.0 Dude
    5.0 Dude April 24, 2010 at 4:58 am

    Do you know what size fan I'd need to fit '91 Mustang with a 5.0 liter engine? And keep the engine cool enough?

  • How to Choose an Electric Fan « Flex-a-lite Blog July 25, 2010 at 10:04 am

    [...] you have measured your radiator and found the Flex-a-lite electric fan that will fit best (if not, click here for more information to help you choose the correct Flex-a-lite electric [...]

  • Radiator -- Aftermarket/Custom Availability??? - Chevrolet Colorado & GMC Canyon Forum August 5, 2010 at 3:00 am

    [...] -- Aftermarket/Custom Availability??? Nice link here for figuring the required cfm for a efan: How to Choose an Electric Fan Flex-a-lite Blog __________________ Join the CAPITAL CHAPTER! PM Chris0nllyn, Downtime Designs or 1BADI5 Notice, [...]

    BRIAN August 7, 2010 at 1:44 am

    I have had a 292 big fan on my suburban for years. Unfortunately my second variable controller has blown and I was smart enough not to mount this one on the fan.
    I love the fan but the controllers suck - especially at $100 a pop replacement cost.

    Can you say - "DESIGNED OBSELESCENCE???????"

    • therealcoleq
      therealcoleq August 7, 2010 at 10:49 am

      Brian -- Sorry to hear that you've had trouble with your variable-speed controller. Usually if you have more than one go out, there is an installation problem. Often it's as simple as an improper ground. Please give us a call at 253-922-2700, and we'll do what we can to help you.

      • Brian
        Brian August 10, 2010 at 8:07 am

        Just spoke the great folks at Flex-a-lite. As frustrating as an expensive part is when it goes, our true USA companies stand behind their products. It was the relay, and it was explained to me that they have gone through several versions. They are sending me a new one to remedy my fan problem. Thanks for the replacement and for standing behind your products.

  • Michael Amos
    Michael Amos January 14, 2011 at 8:07 am

    I have restored a 1967 Mustang convertible with a 289 engine. I would like to install an electric fan with a #31165 controller. I could not find a specific model of fan to buy. Does the controller have a temp probe that can be installed in the intake manifold? The picture shows one but the instructions show the radiator model.

    • therealcoleq
      therealcoleq January 14, 2011 at 10:21 am

      If your Mustang has the 17-inch core radiator, then our Part No. 160 and 168 fans will fit. The 160 comes with an adjustable thermostat and a probe that senses temperature via the radiator core. The 168 comes without controls. You can then use our 31163 variable speed controller with thread-in temperature sensor.

      Of course we would recommend our Part No. 51067 radiator and fan combo which is a direct bolt-in for '67-'69 Mustangs and all ready to go for this application! You can click here for more information.

      • Michael Amos
        Michael Amos January 18, 2011 at 5:55 am

        I have a custom aluminum radiator that has a core area of 16.5 x 16.5 and is 3.75 from the fan pully bolts. It has an unkown electric fan on it now. This fan is on all the time and is very noisy. I also don't believe it has adequate flow during a hot summer day. I want to upgrade to a top of the line flex-a-lite fan with a thermostat control.

        • therealcoleq
          therealcoleq January 18, 2011 at 12:11 pm

          Generally, it helps us to know what type of car and engine specs and all, but in this case, comes down to the room available. The only thing you have room for is our Part No. 118 Low Boy electric fan. This fan measures 16 x 16.5 x 3.1875 inches and it moves 2,500 cfm. With it, you can use either our 31149 control or the 31165 controller.

          Depending on the radiator, this should be good for around 400 horse. You can also call us at 253-922-2700 to get more details or if you have other questions.


  • Mike Doxey
    Mike Doxey July 7, 2012 at 4:45 am

    Did I make a mistake? I have a 77 CJ7 with a small block chevy conversion. 383 stroker with approx 500 hp. I Just ordered one of your Stock duel fan electrics for the stock 4 core rad. After reading this I think I should stick with the engine driven fan. Do you agree? I have also looked at you Alumnium Rad and fan combo but it does not have an oil cooler for the 700R4 trans I recently installed. In your opinion will the B&M super cooler mounted in front of the rad keep the trans cool on its own?

    • therealcoleq
      therealcoleq July 7, 2012 at 11:17 am

      Four core radiators are extremely challenging to pull air through. Sometimes an electric fan works well, but you may want to consider one of our 7-blade flex or fixed-blade belt-driven fans. We don't incorporate a trans cooler into our radiators, and we believe it's a better cooling solution for both the engine and the transmission to have a separate transmission cooler. We'd prefer you use a Flex-a-lite transmission cooler, but if you already own another, give it a try.

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