How to Choose an Electric Fan in 4 Easy Steps

Discussion in 'Cooling Systems' started by Indycars, Oct 4, 2012.

  1. Indycars

    Indycars Administrator Staff Member

    DIY Garage on Summit, How To's by David Fuller

    A couple weeks back, we asked the question: Mechanical vs. Electric Fans: Which is Best for Your Vehicle? If you’ve determined that an electric fan is the best choice for your ride, you’re certainly not alone.

    Electric fans have become the preferred choice for many enthusiasts because they have lots of advantages over mechanical fans, including:

    Good cooling with no parasitic horsepower loss
    Consistent cooling—they maintain their airflow at all times
    Versatility—they can be mounted in front of or behind the radiator
    Multiple sizes and configurations—they can be found in diameters up to 20 inches and are available with single- and dual-fan setups

    The next logical question is: “Which electric fan is right for my vehicle?”

    With help from our friends at Flex-a-lite and input from the Summit Racing tech department, we’ve identified four keys to choosing the right electric fan for your application.

    1. Establish the Need
    If you haven’t read our original post on mechanical and electric fans, start there. You’ll learn that, in some cases, the stock clutch fan or an aftermarket flex fan will work just fine.

    Remember, though, a mechanical fan is driven by your engine. If your engine is spinning at low rpm, so is your mechanical fan—and that means there will be less airflow at lower engine speeds. If you notice your vehicle running a little hot in traffic or at low rpm, an auxiliary electric fan may be just what you need to give your primary fan a cooling boost.

    2. Determine Optimum Airflow
    Companies like Flex-a-lite rate their electric fans by horsepower and airflow levels—simply choose the one that is rated the same as or higher than your vehicle’s power output or airflow requirements.

    Flex-a-lite recommends these minimum cubic feet per minute (cfm) ratings when using an electric fan as the primary cooling source on a basic engine:

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

    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 300-horsepower powerplant regardless of the cylinder count. Again, many electric fans are rated by recommended horsepower to help you get the optimum amount of airflow.

    3. Measure It Up
    Once 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.

    You should also measure the radiator core, which is the finned surface between the two tanks. You’ll want to select a fan that covers as much of this space as possible. In many cases, you will 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. You can supply these dimensions to your sales rep or consult this handy Flex-a-lite chart, which helps match the right electric fan to your dimensions.

    4. Choose Pusher or Puller
    Electric fans are available in pusher or puller designs. Pusher-style fans mount on the front of the radiator and blow air through the radiator core. Puller-style fans mount behind the radiator and draw air through the core.

    Puller-style fans are recommended for applications in which the electric fan is the primary cooling source. A pusher-style fan can be used as an auxiliary cooling source, but you should sure make the fan covers as much of the radiator core as possible. This goes back to measuring and determining the right dimensions for your fan.

    Don’t spend valuable cruise or car show time sitting on the side of the road. Take the first four steps toward avoiding an epic summer meltdown—and keep your ride firing OnAllCylinders!


    Attached Files:

  2. grumpyvette

    grumpyvette Administrator Staff Member

    these links may also prove useful
    great POST!,Indycars

    IF you've asked the rather common question about how big a radiator or electrical fan you'll need on your recently installed or up-graded performance engine, you'll need to do some accurate calculations based on facts not assumptions. of the related useful info.
    Id point out that a great number of performance engines that run too warm, can have the operational temps dropped rather dramatically, if you use a 7 quart -to-8 quart baffled oil pan, and if you add a oil and transmission cooler with an electrical fan, too absorb and remove engine heat before it ever reaches the radiator coolant,Id also point out that up-grading to a 140-200 amp rated alternator can frequently provide the extra current capacity to spin even existing electrical fans a good deal faster rpms than they may currently be able to operate at, as many O.E.M. alternators do not have the capacity to keep up with the cars increased demands for current with some electrical fans.!
    engine cooling is done through several sub systems working as a team, your engine oil absorbs and transfers a a significant percentage of the heat generated to the engines coolant system,the coolant flow rates will effect the engines ability to transfer heat to the radiator, and the fan, shroud if you have one will increase the outside air flows ability to efficiently transfer heat to the outside air.
    first the fan has a CFM (CUBIC FEET PER MINUTE, rating,) (2500 cfm and up is generally a decent start point for a performance engine) but its certainly not going to be enough for every application. ,and all performance cooling fans will have a rated AMP draw,rating (ELECTRICAL CURRENT requirement ) generally this falls in the 40-50 amp range (peak draw) and will quite commonly require a added higher rated, electrical relay to allow switching without damage to the existing electrical wiring, on a performance engine with a single electric fan which your cars electrical system may or may not be able to fully supply, if the alternator is not able to fully supply the fan motor electrical draw, it will not provide the required air flow.
    most stock alternators will not keep up with the increased electrical demands provided by a high performance electrical cooling fans increased amp draw.
    fans generally require a matching fan shroud placed and correctly clearanced on the rear of the radiator to reach the full cooling efficiency, your radiator will generally require about 1.4 square inches of surface area per cubic inch of displacement. your engines water pump must be able to provide the required coolant flow and the t-stat must also not restrict coolant flow rates.
    ignition timing effects the engine combustion and exhaust gas temperatures, so thats important.
    keep in mind almost all the engines heat is generated in the upper 2" odf the cylinders, combustion chamber and by heat generated in the valve train and rotating assembly, thus OIL FLOW rates are also critical as its OIL flowing over the engines moving components that absorbs and transfers at least 70% of the engines higher temps to the block and coolant, thus adding an oil cooler with a fan to also transfer heat absorbed by that mass of oil will further reduce the heat load on the engine coolant!
    guys also fail to realize a properly set up 7-8 quart baffled oil pan and a separate electric fan equipped transmission cooler can go a long way toward reducing the engine temps, a properly set up oil and transmission cooler can reduce the heat loads on a radiator significantly [​IMG]
    with an auto transmission, the heat load the radiator deals with is further compromised by the transmission fluid heat transfer, so adding a trans fluid cooler with an auxiliary fan will again reduce the engines cooling system heat loads.
    its fairly common, but guys often fail to think thru the accessories choices or fail to install a fan shroud that fits both the radiator and fan they use, or fail to get a fan rated at 2500-3500cfm, that will move enough air to effectively transfer the heat out of the radiator and having a decent 3-4 core radiator,aluminum performance design sure helps.
    the dual fan and shroud idea has several merits, it allows very effective cooling and if wired correctly two levels of air flow either manual switch or thermal switch control, and remember a 160 amp-200 amp alternator helps increase fan speed noticeably by providing extra current capacity
    obviously theres a huge variation in both fan size and efficiency and the power they can provide to drag airflow thru the radiator, so shop carefully, and don,t ignore salvage yards where theres dozens of options at low cost.
    you could easily spend $500 on a new set with shroud and relays, in the set-up that pulls well over 4000fpm, but that may not be required, and there are dozens of options like selecting fans and shrouds from salvage yards... Ive frequently measured and selected used fans and shrouds from late model wrecks and paid well under $70 for a complete set-up
    FORD TAURUS fans are popular choices from salvage yards



    Dorman 620-118 Radiator Fan Assembly

    If your replacing a damaged or missing fan shroud ,it doesn,t need to be an EXACT match,to the original O.E.M. component
    but it should be an IMPROVED design over what its replacing'
    in both structural strength and ideally in cosmetic appeal,
    a bit of custom fabrication if done correctly,
    will add rather than detract from the over all builds visual and functional presents,
    ideally you want people to look at what you've done and think
    "WOW! why didn,t I think of that!.... DAMN THATS IMPRESSIVE"
    rather than "
    what the hell was that guy thinking when he installed that crap!"

    and sometimes
    the difference is only in a few extra minutes grinding welds,
    the type of fasteners used, the care taken in the fabrication and careful fitting,
    thinking through the over all design,
    or a bit of matching paint


    [​IMG] OUTSIDE air travels from the front of the car, toward the engine, thru the radiator where it absorbs and transfers heat from the radiators fins to the airflow,so fans behind radiator PULL those in front PUSH air toward the engine thru the radiator
    I don,t understand guys thinking the stock cooling system will be adequate once they double an engines power output, the fact is increased power by definition required increased rates of fuel being burnt and that generates higher heat and increased stress and internal engine friction.
    and guys also fail to realize a properly set up 7-8 quart baffled oil pan and a separate electric fan equipped transmission cooler can go a long way toward reducing the engine temps, a properly set up oil and transmission cooler can reduce the heat loads on a radiator significantly

    keep in mind, that puller fans, especially with a well matched shroud fan are significantly more efficient than pusher fans at moving air thru a radiator,Id also point out that the higher the air flow rate the more effecive the heat transfer will tend to be,and that larger capacity aluminum radiators ,will provide significantly more surface area for that heat transfer to use.

    yes theres a great deal more info in the sub links



    viewtopic.php?f=70&t=3504&p=33365#p33365 ... cessories2 ... cessories2




    Last edited by a moderator: Aug 12, 2018
  3. DorianL

    DorianL solid fixture here in the forum Staff Member

    I run dual electric pullers + shroud. They are GREAT. Even on a real hot day I will only need one fan and it will take me down to 150. (I know, too cold. I just have a phobia of hot engines...)

    Derale 4000 CFM


    I am VERY happy with them... GREAT buy! $214
  4. grumpyvette

    grumpyvette Administrator Staff Member

    I used a very similar electric fan set-up recently on a guys 1967 GTO after we installed a 468 BBC, engine in it, along with a 7 quart oil pan and an oil cooler with a new 4 core aluminum radiator, the upgraded cooling system , well, it was amazing in that it held temps to a nearly rock steady 180F -185F,even when he was beating the crap out of the car, thats unusual, because in most cases coolant and oil temps tend to climb, but those temps fall as soon as the higher loads and rpms are reduced, in this case the oil temps tended to climb a bit as usually , but had a hard time reaching the 215f I like to see the oil hit under higher rpms,but the coolant temps stayed fairly steady, just barely increasing until the t-stat opened then dropping back rapidly, at first I thought the gauge might be defective but checking with an IR temp gun showed the radiator was dissipating the heat rapidly when the thermostat was opening, and because Id drilled (6) 1/8: holes in the t-stat flange it took a good long time to even reach 180f,and once the t-stat opened it might reach 185F but then drop back, as a significant coolant flow rate was present even when the t-stat was closed, once it opened there was even more cool coolant flow.
    and yes the car was wired with a relay so that both coolant fans on the radiator and the fan on the oil cooler,came on at full speed as soon as the ignition was started.
    hes been driving the car like that for about 6-7 months now with zero issues
  5. grumpyvette

    grumpyvette Administrator Staff Member

    If your running dual electric fans its fairly common to have two temp switches so that one fan comes on only if the engine exceeds about 220 F while the first fan comes on at about 190F , this is usually with a matching 180f-or-190F thermostat. so that under normal operating conditions the engine coolant tends to stay in the 190F-195F range.
    dorianL has the correct idea! have the components in place and ability to pull excess heat out of the engine rapidly, dual fans a decent fan shroud and a aluminum radiator that easily allows you to effectively dissipate heat is a really big plus for engine durability, having a separate transmission fluid cooler sure helps if your running an automatic transmission ... structions
    if you want to simplify the wiring you can have one fan operate any time the ignitions got voltage and the second wired to a temp sensor for its ground circuit

    (1) the larger the heat transfer surface area the better the system tends to operate, but a minimum of about 1.5-2 square inches of radiator fin area exposed to effective air flow per cubic inch of displacement is generally required
    (2) oil does much of the initial heat transfer in the engine, keeping the oil cooled to no more than about 15F above the coolant temp, reduces the heat load on the radiator coolant, so adding a high capacity 7-8 quart oil pan and fan equipped, remote mounted oil cooler can dramatically reduce engine operational temps.
    Dorman 620-118 Radiator Fan Assembly
    (3) air flow rates are critical so a well designed fan shroud and a fan(s) easily capable of pulling 3000 plus cubic feet per minute in air flow is very helpful

    unfortunately that type of electrical wire, repair work is almost a fore gone expectation with an older muscle/performance car,
    but with patience and a decent 350 -400 watt solder gun and some, flux, lead/tin solder and shrink tube its repairable,
    just be sure to slip on the shrink tube insulation, and clean and flux the connections before soldering

    Last edited by a moderator: Apr 5, 2018
  6. grumpyvette

    grumpyvette Administrator Staff Member

  7. grumpyvette

    grumpyvette Administrator Staff Member

    sensors generally get 12-14 ga anything that carries serious amps is probably 10 ga
    and if its for a starter or alternator, or battery it is probably significantly heavier gauge, if your replacing a broken wire you can of course measure to find the old gauge size Section/Solar Panel & Charge Controllers/WireGaugeSelectionTable.pdf
    this is how a relay should wire
    If you want a direct circuit, wire #87 needs to go to one side of toggle switch and #30 to the other, side of a
    be sure you use a 40-50 amp rated toggle switch, and a good ground with stranded 10 ga copper wire or youll be replacing toggle switches frequently

    the answer too what cooling system is most likely to both cool the car/truck efficiently and fit your budget,would mostly depend on your budget limitations,
    but a large 3-4 tube aluminum radiator with a a 140-to-200 amp alternator
    taking advantage of all your options is a smart way to reproach the issue of correctly controlling, and maintaining a stable and predictable engine heat level, thus installing a larger capacity racing style oil pan and an auxiliary oil cooler with an electrical fan, will significantly increase the engines ability to rapidly dissipate heat even before that engine heat is absorbed by the engines cooling systems coolant. oil flow over a few of the hottest components like valve springs, bearing surfaces,and rocker arms absorb and transfer heat to the block, and oil pan as it flows, thus a larger oil capacity and a baffled oil pan with an extended sump is a good idea as the increased oil capacity and larger surface area of an enlarged sump area exposed too outside air flow can stabilize and allow a good deal of heat to dissipate to that outside air flow, as the air which can be well over 130F-170 plus F cooler that the engine oil that can be up to 250F plus in a racing engine


    I'd point out that a 7-8 quart baffled oil pan helps cool an engine.
    and dual or a large single electric fan with a matched ducted shroud and the ability to move,
    2500 fcm-3000 cfm of air should provide adequate cooling for most engines.
    adding an auxiliary oil cooler certainly helps
    Keep in mind a well designed 7-8 quart baffled oil pan adds both durability and helps reduce cooling issues
    and if you have an automatic transmission Id add a electrical fan cooled trans fluid cooler


    Last edited by a moderator: May 21, 2017
  8. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    Project K1500: Electric Fan Install
    Keeping your Engine and Tranny Cool without Emptying your Wallet
    Mar. 24, 2008By Jarred Meyer
    If you are like me, you may have noticed that when getting a bit rough with your truck on the trails the engine quickly starts to build up heat. So you stop and let the truck run in idle hoping it will cool down. To your surprise, after waiting a few minutes it hasn’t begun to cool. You pop the hood to find that the fan is barely moving. This is because the stock mechanical clutch-driven fan is only designed to move at the speed of the engine and is not built to keep up with the slow speed, high power demands of crawling up rocks or through the mud. After searching far and wide I finally found a solution for keeping my engine running cool. Through some searching on the internet I found that you can prevent this problem by switching to an electric cooling fan.
    There are multiple benefits to using an electric cooling fan over a mechanical fan. First of all, when you are using the fan on a rig designed for riding through the mud or on the trails, you can have the fan running at full speed while the engine is running low RPMs. Another benefit to switching from a clutch-driven fan to an electric fan is the gain in horsepower you get by taking the added strain off of the engine.

    Some people say that where you gain HP by removing the mechanical fan you end up losing it again by adding strain on the alternator and electrical system. I can tell you first hand that the only strain I notice is just the initial start-up of the fan. Beyond that the truck has a noticeable gain in power. Another point to this debate is that the mechanical fanis almost always adding strain to the engine, even when it is cool. The electric fan, on the other hand, can be switched on only when it is needed. I have been running this setup through the winter and have actually only needed to turn the fan on once, which was due to a steep climb up a snow covered road in two-wheel drive.

    Once I decided on an electric fan I had to figure out which one to get. There is a countless number of possibilities on the market, in a wide range of prices. Initially I was going to cough up around $500 for a high-end dual fan set-up - but then one of my friends (who spends a lot of time in junkyards) came to me with an electric fan out of a Lincoln Mark VIII. Although I could not confirm it, he told me that this fan puts out around 4300 CFMs, which is more than just about any other stock cooling fan out there. He also told me that this particular fan can be found in any Mark VIII between the years '92-'96 which makes it an easy-to-find part at the junkyard. I bought it from him for $20.


    The electric fan I used was stock from a 92-96 Lincoln Mark VIII.

    Now that I finally had a fan, I needed to figure out a way to mount it in place of the existing fan and shroud. At first glance, the task appeared to be a rather difficult one. However, once I removed the old fan shroud I was able to develop a plan. While the existing fan is in place, you have to remove the old fan shroud in two pieces.


    Once removed, you realize that you will be able to use the existing fan shroud in conjunction with the electric fan.

    After I removed the fan shroud and set it aside, I then removed the old fan and clutch assembly from the pulley. Be sure you reinstall the four bolts onto the pulley that held the fan/clutch assembly or you will end up losing the belt and pulley down the road.


    Remove the existing fan/clutch assembly by backing off the four nuts from the fan stem to the pulley.

    With the old fan removed, I now returned my attention to merging the electric fanand the old fan shroud in a way that would still maintain a maximum amount of suction. To do this I first bolted the two halves of the fan shroudback together and test fitted into the truck to make sure I could slide it back in its place without any conflicts. The only problem I ran into was the lower radiator hose and lower tranny cooler line. To allow the fan shroud to easily pass by these, I simply cut notches into the bottom corners of the shroud.


    Slight modifications were made to the 2 existing fan shroudhalves to allow it to be reused in the installation of the electric fan.

    Installing the electric faninto the existing shroud also turned out to be pretty easy. The only modifications I had to make were to cut the left and right side flanges off and clip off one of the lower corners. Then, with a little bit of persuasion, I was able to get the modified electric fanassembly to fit right inside of the old shroud. I drilled some holes through the top and bottom flanges of the electric fan assembly and old shroud and simply installed some bolts to hold the two together. This allowed for the maximum amount of air flow through the radiator and tranny cooler without losing too much suction through any holes.


    A few modifications to the electric fan assembly allowed it to be installed easily into the old fan shroud.


    That completed the merging of the fan shroud and Mark VIII electric fan and it was now time to install the new fan assembly into the truck, wire it up and test it out.

    Now, like many of my other wiring projects, I cut a few corners knowing that I will be rewiring the truck in the near future anyway. Besides, I was anxious to see how well the fan worked! Using a few relays and grounding the assembly to the closest bolt, I could just about completed the wiring side of the fan. I ran a wire into the cab and hooked it up to one of my auxiliary switches and I was ready to go. It is possible to get a thermostat to use with the electric fan so that you don’t have to be continually monitoring the temp gauge, but as I found out driving around a bit, you will know when the fan needs to be running. Another advantage to running the fan on a switch is that you can turn it off if you are going to run through some deep water to avoid damaging the fan.

    Now that the installation was complete I jumped into the cab and switched the fan on to make sure it worked. The fan started up instantly and sounded similar to a jet powering its engines up for takeoff. It was a very reassuring sound, and I could tell this fan was definitely moving more air than the stock mechanical fan ever could. I turned the fan back off and started to drive around to get the temperature up higher than normal so I could see how quickly the fan would recover. As I pulled up to a stop light I watched as the temperature gauge climb up to around 240. I quickly switched the fan on and to my amazement the rising temperature was instantly put into check and began to fall back down. On the way home I did it again and timed it to see how quickly it recovered. I was amazed to see the temperature back to normal within 60 seconds.


    Using the electric fanfrom the Mark VIII turned out to be a complete success!

    Replacing the stock cooling fan on Project ’93 K1500 has been one of the most effective low-budget projects I have done. (Maybe minus the snorkelof course. I will get the truck into some deeper water once the interior and wiring will handle it.) I got the truck out to a local mud fest a few weekends ago and was really working it hard - it never came close to overheating the engine. I would definitely recommend this project to anyone who wants to use their truck for even the lightest off-road driving.

    if coolant in the engine gets hotter faster at idle than when your cruising the cause is frequently related to either a lack of air flow (not the correct fan or shroud)
    or not enough functional radiator surface area,as the car speed increases it obviously has the effect of increased air flow that results in more efficient heat transfer rates
    yes the idea of a larger radiator with increased surface area helps.
    most of us are forced due to clearance limitations to select a radiator with specific width and height limitations you can frequently select a radiator thats a bit thicker,
    or has a higher fin count per square inch of surface or more efficient inner coolant tube designs.

    reading links helps
    Last edited: Jun 16, 2018
    william ritchie likes this.
  9. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

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