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Electric thermo fan ...CFM ?

Discussion in 'The Hokey Ass Message Board' started by Talkwrench, Feb 13, 2013.

  1. Thinking about running a thermo fan on my 21 stud flathead, I have a 12 volt alternator and I'd like to remove the fan off it before it buggers the bearing. And of course have better cooling.
    Question being; how big does the fan need to be and what sort of CFM would be required.
    Im looking at a 16" job that has a 220 watt motor with a controller that cuts in a 185 and comes off at 175.
    I have talked with the guy selling them had said that it will do over 2000 CFM.. Also said be sus about the ones claiming high CFM its mainly BS !

    SO is over 2000 CFM enough??
  2. swifty
    Joined: Dec 25, 2005
    Posts: 1,748


    First do not remove the fan off your alternator as the one thing that kills alternators is heat and the fan is there to keep it cool.

    Re your fan capacity I'm running a 14" Spal pusher fan on my 32 which is only 1275CFM. The only time it cuts in is when I'm doing 5mph along the dirt road to our house and it's on a 185/175 cut-in and cut-out. It does cut in if I get caught in traffic but most of my miles are country miles. Engine is a basically stock 318 Poly. Fan draws 11 amps which equates to approx 140w. What brand is the fan you are considering?
  3. I would stick with spal or similer quality fan. There is a lot of junk on the market.
  4. Weasel
    Joined: Dec 30, 2007
    Posts: 6,694


    It's all in the amps. There is a load of BS written on this subject and false unsubstantiated claims by less than honest sellers. If it does not draw the amps, the motor is not powerful enough to pull the cfm. If you install a fan with a big current draw you may have to upgrade your alternator to at least 100Ah and used a suitable fan relay of 70 amps. Check your alternator's output at idle - 1 wire alternators do not usually cut the mustard in this respect. Use name brand fans only. SPAL, Maradyne are a couple of the better known. my favorite for versatility and flow are those from Cooling Components Inc. - 2600/2700 cfm with a shroud and only 2-5/8 deep at the motor. The installation below shows a total depth of under 5" - that's for the fan and radiator!!! I have two in different vehicles with space problems and these are just the ticket....


  5. 4tford
    Joined: Aug 27, 2005
    Posts: 1,720


    I have the 2700 CFM cooling components fan and shroud on my 40 with a 392 hemi and it does the job. I needed 4 1/2 inches of space and their fan fit perfect for my application.
  6. 2000 CFM at what pressure drop??? 2000 CFM is a completely worthless number unless the manufacturer provides the pressure drop that particular flow rate occurs at. A proper fan manufacturer will provide performance curves for their fans. All radiators create a pressure drop as the air flows across the fins. The more densely packed the fins or the thicker the core, the higher the pressure drop. If the fan is rated at a maximum flow rate of 2000 CFM at 0 in/H2O pressure, then this tells you absolutely nothing, because the fan may be flowing alot less when it is bolted to your rad. You need to look at the fan curves. The chart below shows the performance curves for Spal's 385 mm (15 in.) fans. The curves represent different blades, motors, shrouds, etc. In order to maximize fan performance, you want a fan that maintains the highest flow rate at the highest pressure drop. Also, don't forget to look at amp draw, higher flow usually requires a motor that draws more amps. No one looks good when their lights dim every time the fan kicks on.

    Last edited: Feb 14, 2013
  7. I think they would just about all be rated without the pressure drop...Pfft! cant see anyone being honest about that .. They would simply say "well we dont know how thick your radiator is ??"
    The one I was looking at draws 10amps running.. Its only 3.7" thick. space is a premium, I want it as a puller.
    I do have a GM 80amp alt, guess its basically a 1 wire however I have it as a 3.. I have brigded the wire to position 2 to excite it early.. Still not that good as it doesnt go to 13.5 at idle has to be up around 1200rpm..
  8. Gman0046
    Joined: Jul 24, 2005
    Posts: 6,260


    Most CFM claims are BS. Buy the biggest Spal fan that will fit. Spals will flat out blow your hat off. They don't use them on Ferrari's for nothing.
  9. I think I will take a college math class before I read further .... ;)

  10. Jim Stabe
    Joined: Oct 31, 2008
    Posts: 179

    Jim Stabe

    I would use an OEM fan rather than one of the aftermarket ones. The Ford Taurus has a great reputation for a good reason. Another fan similar to the Taurus is available on Volvo cars, it is about 1/2" smaller in diameter (about 16 1/2"), uses the same motor as the Taurus and has a really nice mounting ring built in to mount it into a shroud. Get the relay pack that it comes with also so you can run both high and low speeds.



    Volvo on shroud.jpg

    Volvo wiring-1.jpg

    #1. You need 2 temp switches for 2 speeds. (Choose the one you prefer)
    Solution #1 = BMW 80 / 88* C (180/195*F) dual temp switch Part # 61318361787 < $16 from Rock Auto
    80*=176 88*=190<o:p></o:p>

    Solution #2 = BMW 91 / 99* C (195/210*F) dual temp switch Part # 61311378073< $11 from Rock Auto - can't beat that. <o:p></o:p>
    One single temp switch instead of 2, just gotta drill and tap a brass adapter fitting to accept the M14 x1.5 thread.<o:p></o:p>
    <o:p> </o:p>
    I found the sensor and pigtail in the junkyard on a 1995 BMW 535. I would say pretty much any inline 6 BMW from of this vintage will likely have this sensor arrangement. Look for 88-96 5 series and 92-99 3 series. On the 5 series it was directly behind the inboard passenger side headlamp sticking off the side of the radiator tank.<o:p></o:p>
    <o:p> </o:p>
    Found the switch for $10 @ RockAuto,107,61311378073

  11. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,623


    I use a pusher on my 35 Chevy and a puller with shroud on the 46 Olds, 1800cfm I think?
  12. I'll have to see if I can find something with a shroud, seems like the way to go.. I'll look around for a spal, over here they are just damn expensive!

    thanks for all your input..

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