Flex Fan vs Clutch Fan

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Nikkormat
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Flex Fan vs Clutch Fan

Post by Nikkormat »

So, I've got a flex fan, and a clutch fan. Both are the same size and same distance from the radiator. Which one would offer the best cooling performance?
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Re: Flex Fan vs Clutch Fan

Post by Stuka »

clutch fan, hands down. Flex fans stop moving air once they hit a certain RPM. And even at low rpm they move less air. You may lose a negligible amount of power with the clutch fan, but it will cool better. Well, provided the clutch is working properly.
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Re: Flex Fan vs Clutch Fan

Post by 68glad »

Flexfans are good for flowerbed windmills.
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Re: Flex Fan vs Clutch Fan

Post by FSJunkie »

Both accomplish the same task of reducing parasitic power draw on the engine at high RPM, just they do it in different ways.

Clutch fans are quieter because they limit their RPM, but wear out.

Flex fans never wear out because there are no moving parts, but are noisier.

...there is still a third type: the thermostatic clutch fan. These slip all the time and keep the fan at very low RPM under all conditions until the air moving through the radiator gets hot enough for the clutch to automatically engage. Then it becomes a regular clutch fan. These are VERY quiet and are better in cold weather because the fan will basically stay disengaged the whole time.

Any of them is better than a fixed fan. Those puppies are noisy as all heck and suck 10 horsepower.

1. Thermostatic clutch fan.
2. Flex fan.
3. Clutch fan.
4. Fixed fan.
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Nikkormat
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Re: Flex Fan vs Clutch Fan

Post by Nikkormat »

My clutch fan is thermostatic, but the thermostat makes little to no difference in fan speed. I think it is broken. But it still operates at a normal clutch fan. Is it still safe to use?
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Re: Flex Fan vs Clutch Fan

Post by Herk »

Flex fans don't wear out?!? BS! Sooner or later the blades will crack from flexing and become projectiles. Been there, done that, bought the radiator.

Flex fans flatten out at high RPM, so when the engine is making the most heat, the fan is moving the least air.

I can't think of an engine driven fan on any engine built in the last 35 years or so without a clutch. And can't think of ANY factory installed flex fan on any engine EVER.
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Re: Flex Fan vs Clutch Fan

Post by Stuka »

I have seen flex fans go through hoods. They most certainly wear out! The rivets get loose over time, and I have seen them get stress cracks.

Nikkormat: Your factory clutch fan does lower fan speed compared to direct drive. With the engine off, grab the fan and see if it wobbles. If it doesnt, its safe to use. The clutch may or may not be worn out. When they do wear out, the fan spins slower, as opposed to faster.
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Re: Flex Fan vs Clutch Fan

Post by serehill »

Herk wrote:Flex fans don't wear out?!? BS! Sooner or later the blades will crack from flexing and become projectiles. Been there, done that, bought the radiator.

Flex fans flatten out at high RPM, so when the engine is making the most heat, the fan is moving the least air.

I can't think of an engine driven fan on any engine built in the last 35 years or so without a clutch. And can't think of ANY factory installed flex fan on any engine EVER.

Yep this is fact they don't function as well as a clutch fan. They don't last as long they will cut the crap out of you. When they do come apart they love to take hoses lines radiators etc. Take a piece of thin metal & bend it back & fourth to see what happens to flexing metal. No rocket science to it. Everyone has their preference & opinions. Thermal units are very similar to friction clutch units. & in my opinion not worth the difference in cost. Flex fans are not for me. I wouldn't swap. The parasitic value isn't worth the difference. BUT there were some factory flex units. Flex a lite has been around over 40 years there's a reason why they aren't more popular than they are. Clutch fans too are on their way out. No automobile today has one for good reason, but that is another thread. If parasitism is a concern do the real math on electric. That's the forth & most popular on the market today.
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Re: Flex Fan vs Clutch Fan

Post by Stuka »

serehill wrote:
Herk wrote:Flex fans don't wear out?!? BS! Sooner or later the blades will crack from flexing and become projectiles. Been there, done that, bought the radiator.

Flex fans flatten out at high RPM, so when the engine is making the most heat, the fan is moving the least air.

I can't think of an engine driven fan on any engine built in the last 35 years or so without a clutch. And can't think of ANY factory installed flex fan on any engine EVER.

Yep this is fact they don't function as well as a clutch fan. They don't last as long they will cut the crap out of you. When they do come apart they love to take hoses lines radiators etc. Take a piece of thin metal & bend it back & fourth to see what happens to flexing metal. No rocket science to it. Everyone has their preference & opinions. Thermal units are very similar to friction clutch units. & in my opinion not worth the difference in cost. Flex fans are not for me. I wouldn't swap. The parasitic value isn't worth the difference. BUT there were some factory flex units. Flex a lite has been around over 40 years there's a reason why they aren't more popular than they are. Clutch fans too are on their way out. No automobile today has one for good reason, but that is another thread. If parasitism is a concern do the real math on electric. That's the forth & most popular on the market today.
Actually Ford and GM HD trucks use clutch fans. Not sure if they are thematic or not. They are plastic so that there is less rotational mass.


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Nikkormat
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Re: Flex Fan vs Clutch Fan

Post by Nikkormat »

IHC did use flex fans on their implementation of the 401. That's where I got mine.

Looks like I'm sticking with the clutch fan. Thanks again guys!
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Re: Flex Fan vs Clutch Fan

Post by FSJ Guy »

X2 on the fan clutch. Using that with the OEM fan will also reduce the chances of slicing your fingers/arms on the sharp blades of the flex fan.
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Re: Flex Fan vs Clutch Fan

Post by The PIG Smith »

Some of this was cut and pasted from the 'Mothership'

The 2797 is the Heavy/Super Duty version of the Hayden Fan Clutch..

The regular fan clutch probably spins at 60% of engine rpm.
The next up spins at around 70% engine rpm.
The 2797 spins at 90% of engine rpm.
The 2797 IS LOUD, as it moves more air all all engine speeds.

This means that you get superior low rpm, like crawling through the desert in 115-degree F temps with the AC full on, at 20mph or less, and still keep cool, with other mods in the system.

http://www.haydenauto.com/upload/hayden ... clutch.pdf

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Re: Flex Fan vs Clutch Fan

Post by FSJunkie »

AMC passenger cars used factory flex fans. Got one on both my 1973 and my 1977. They look slightly different from the Flex-a-lite fans bought aftermarket, but are a flex fan none the less. I'll let people know when they fly apart, if I'm still alive when it happens. (Double pun there ;) )

Don't think fixed fans fly apart as well? They're under even more stress than a flex fan since they have greater mass around their circumference and CAN'T flatten out. They have to slug through the air at high RPM, which produces tremendous stress on the vanes. Put a timing light on a fixed fan at 4000 RPM and see what it does.

Increasing fan speed increases airflow up to a point where airflow tapers off but power draw continues to climb. No point in speeding the fan up past that point because it only draws more power and doesn't help cooling any better. Flex fans may not limit their speed, but limiting airflow through vane pitch above the airflow taper-off point accomplishes the same goal. Neither cool better or worse than a fixed fan if designed properly.

A thermostatic fan clutch just slips more in cold and less in hot. It's not on and off; they slowly transition. Wintertime you won't hear the fan at all. Summer with the A/C on that fan clutch is tighter and you can hear the fan then. They don't fully tighten up until the engine starts running a little warm, like 200-210 on the gauge, and then they ROAR.
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Re: Flex Fan vs Clutch Fan

Post by serehill »

All of that is Hocum offroad in low range.

Semi flex factory fans apples to oranges.
All fans flex to a point.
Anything assembled with bolt, rivets or mechanical selection rotated @ 5k rpm can disintegrate.
You can save 15% in 15 seconds on your car insurance.

Electric fans still out perform all of them. They are not dependent on engine automobile speed they cool when you need it & don't when you don't need it.

For what you're doing the clutch fan rocks Nikkormat
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Re: Flex Fan vs Clutch Fan

Post by FSJ Guy »

The Hayden 2797 is no longer available in a "slotted" bolt pattern. You have to get a HD clutch (not Severe Duty) instead. IIRC, I used a mid to late 80's Chevy truck to find one with the right hub diameter, etc.
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Re: Flex Fan vs Clutch Fan

Post by Tad »

FSJ Guy wrote:The Hayden 2797 is no longer available in a "slotted" bolt pattern. You have to get a HD clutch (not Severe Duty) instead. IIRC, I used a mid to late 80's Chevy truck to find one with the right hub diameter, etc.
I simply cut it with a zip wheel, works fine for the AMC V8's that way.
Have one on the BBCaddy in the Pushmobile too, that baby can move some air.
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Re: Flex Fan vs Clutch Fan

Post by fulsizjeep »

Clutch fan and fan shroud has my vote.
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Re: Flex Fan vs Clutch Fan

Post by kyamcalvert »

I just did away with the factory fan in my girlfriend's 1998 Trooper. Grabbed an electric fan from a 90s Ford Escord for 15 bucks from the junkyard, got a Hayden fan controller for 35 more and wired it all up this weekend. It's extremely quiet, cools great, has adjustable thermostatic control, and was really a cheap mod. I'd do it on an FSJ with no fan shroud in a heartbeat.
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Re: Flex Fan vs Clutch Fan

Post by fulsizjeep »

If you must...
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Re: Flex Fan vs Clutch Fan

Post by FSJ Guy »

Tad wrote:
FSJ Guy wrote:The Hayden 2797 is no longer available in a "slotted" bolt pattern. You have to get a HD clutch (not Severe Duty) instead. IIRC, I used a mid to late 80's Chevy truck to find one with the right hub diameter, etc.
I simply cut it with a zip wheel, works fine for the AMC V8's that way.
Have one on the BBCaddy in the Pushmobile too, that baby can move some air.
Good idea. You didn't have balance issues with that, though?
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