Considering Cooling Fans- Flex

imp

Mustang Master
Jul 13, 2017
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I'm running the '93 spec. 9-blade plastic fan with the correct thermal clutch in my '94 GT 5.0. It's holding the temperature far more constant than the factory electric fan did. A/C still throws real cold, even right after
starting up when the fan clutch is still "cold". So, no problems, just as my '93 Cobra worked.

Not about my present thinking, though. We kicked around flex fans before; some swore yes, the best, some swore at them. Anyone care to take a crack at really trying to figure them out with me? There are imponderables, be aware.

Literature claims flex fans throw maximum air at lowest speeds, less at higher fan speeds, thus saving power over a fixed-blade. Is it really so? What exactly flattens down those blades? Force applied by the air. To flatten them takes maximum force; try it with your fingers, bending the blade back. If they're moving LESS air at higher speeds, what the hell is flattening them? That's an imponderable.

The angle of pitch determines mostly how much force is exerted against the air. Airplanes can "feather" their "fans" to zero pitch, a flat rotating disc, pushing NO air. Or, negative pitch, to slow the plane. So, if the flex fan's blades reach flat, no pitch, they are moving no air! Can't happen, I don't think. Your thoughts?

Imagine a flex fan spun in a vacuum. No air to move. Would axial forces due to the shape of the blades tend to flatten them? Only if they were cut in such a way that centrifugal force would act on them to make them flatten. Does not look like they are made that way. I've always thought of the flex fan as a power-robbing device, maybe better than a fixed blade, but inferior to the clutch fan. Yet, they have been supplied as OEM from the factory. One guy on another Forum (Mavericks), stated his '73 came with a flex fan from Ford. This I don't remember.

Help me to figure out these dag-goned things! imp
 
Cant beat a proper operating fan clutch when compared to a flex fan. Flex fan better than fixed, fan clutch better than flex, proper electric fan set up is the best. A flex fan flexes based on load across the blade. The load has to stay constant to keep it flattened. It is less drag than a fixed fan at same rpm, assuming fixed has equal number of blades at same pitch as flexed at rest. Ever seen or heard a fan clutch that has gone bad and will not freewheel? They make a hell of a racket at higher rpm's. Lots of load/drag.
 
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I ran a flex fan for a few years. At idle it pulls a lot of air. As rpms increase the load on the fan increases flattening the blades. This happens over and over again.

The only down fall is the rivets that hold the blades can loosen....and send a blade into your nice aluminum pressurized radiator...sending a mess of green crap all over a nicely painted engine bay.

Been there done that....never again.
 
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Once again your over thinking things.
Clutch fan works fine. If it malfunctions, it locks in, becomes a fixed blade fan and cooling continues, fool proof, unless of course, it falls off.
If it ain't broke, don't fix it.
@karthief
I respectfully disagree. For several reasons. If we fail to "overthink" things, do we not fall prey to the fish-mongers trying to sell us a bill of goods based on some BS they include in pushing their product? We succumb, blindly, buy the G.D.n'd thing, and find out we've lost ground, rather than gained.

You prefer to approach understanding the plight of keeping these machines running by believing claims? Hard to imagine, given your usual careful focus.

I really would like to see some acceptable explanations and comparisons to either prove, or dispel, the claims for and against flex fans. I think we're close, unless you stop me in mid-tracks...... imp
 
Somewhere, some astute guys have figgered out what really happens with the flex-blade fans. I haven't, but would love to see data taken off a given application regarding fuel consumption, cooling efficiency, vehicle speed and climate conditions rolled into a comparison between flex and anything else.

IOW, am I foolish for using this clutch fan instead of a good flex fan? imp
 
@karthief
I respectfully disagree. For several reasons. If we fail to "overthink" things, do we not fall prey to the fish-mongers trying to sell us a bill of goods based on some BS they include in pushing their product? We succumb, blindly, buy the G.D.n'd thing, and find out we've lost ground, rather than gained.

You prefer to approach understanding the plight of keeping these machines running by believing claims? Hard to imagine, given your usual careful focus.

I really would like to see some acceptable explanations and comparisons to either prove, or dispel, the claims for and against flex fans. I think we're close, unless you stop me in mid-tracks...... imp
You even over think thinking.
Ford did use a flex fan, it was short lived and I think the reason was the thin metal blades cracked and the one I used on a old car cracked and the blade tore up the metal shroud, slicing a hose and generally traumatizing me.
Get off the flex fan train and think about put'n a shroud on that clutch fan retro-fit.
 
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Here is my take on this thread.
Imp is a thinker :thinking:if something works he wants to know how and why, then he thinks of ways to make it better, more efficient, he seems to be smarter than the average person and likes to 'tinker' with stuff, I just wish he'd put a damn shroud on the clutch fan conversion and stay away from 'flex' fans before he is typing with little stubby fingers! :stick:
 
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If you eventually install electric fans then keep animals and small kids away from the front of the vehicle. Some deranged guy here skinned his cat that way...and PETA scared him so bad he was afraid to show is identity ( box ).

Surprised madmike1157 hasn't chimed in on this fan debate
 
If you eventually install electric fans then keep animals and small kids away from the front of the vehicle. Some deranged guy here skinned his cat that way...and PETA scared him so bad he was afraid to show is identity ( box ).

Surprised madmike1157 hasn't chimed in on this fan debate
The guy has a working solution.. As to wondering "why or how" it works, is a conversation for somebody else.
If it works, and solves the problem than I'm satisfied with that...

Just because my pushrod doesn't wear out doesn't make me wonder which heat treating/hardening process is better, or could've been...As long as my pushrods or guide plates don't end up as metal shavings in the bottom of my oil pan, I'm happy.
 
Here is my take on this thread.
Imp is a thinker :thinking:if something works he wants to know how and why, then he thinks of ways to make it better, more efficient, he seems to be smarter than the average person and likes to 'tinker' with stuff, I just wish he'd put a damn shroud on the clutch fan conversion and stay away from 'flex' fans before he is typing with little stubby fingers! :stick:

No mention of actually having a cooling system or cooling fan issue. If the fan could be improved upon, I am sure any improvements in his application would be so small as to negate the time and effort required to implement it. Better if one concentrated their efforts in other areas for real improvements.
 
Imp actually went backwards, he installed a clutch fan, replacing his factory electric fan on a 94 mustang. I think he just went back in time, not efficiency, clutch fans are very efficient.
Having appreciated your commenting, and given "likes" (but not truly sure why), perhaps now yer vying for "thinker II". Isn't what you said above contradictory?

Originally, I questioned Ford's wide "spread" between turn on and off temps. for the electric fan. But I can appreciate that turning it on and off too many times eventually causes failure. What prompted my attention was when I first got the
car, and the Desert was just starting to really heat up (early May), I spotted the temp. gauge climbing like mad, and thought "Aw, :poo:!". Then it leveled off near the top end of "normal" (some gauge calibration!), and started to slowly come down. Then came the "electric dawn".

Having owned 3 Foxes, all 5.0s, all in Desert heat, one a '93 Cobra, I never had a single problem with the factory fans & clutches, other than minor cracking I noted on the '89 fan hub, which Ford Parts confirmed was addressed, and a new plastic introduced, with new part #. I figgered why not put a similar setup on the '94? Not a "snap" because in '94 the water pump hub pilot diameter was increased from 5/8" to 3/4"; nobody has a clutch (that I could find) with a 3/4" hole. Options were enlarge clutch pilot hole (difficult to hold for machining, and then ya got a one-on bastard clutch), or make a spacer-adaptor with appropriate pilots, easy, and needed to bring fan closer to radiator. So far, it holds dang steady temperature-wise, just as it did in my Foxes.

But what's wrong with trying to understand the real facts behind the flex concept? Is it really any good, aside from blades coming off, etc.? Some swear by them, claim superiority in both cooling and economy of operation. I've never been convinced of either claim, but would like to settle the case. imp
 
I would be highly surprised if the even that fan pushed more than the clutch fan. I think they are about as beefy as they come though.
@Noobz347
Another imponderable is that the viscous clutch never really can "lock up" as though it were driving a fixed, solid blade. That may be why the blades often used with them are as big and multi-bladed as possible. What's unknown is how much "slip" is the minimum they allow, when driving at the max. Have never seen such reference. imp