Cooling
Le Mans Master
Joined: Nov 2001
Posts: 8,701
Likes: 1,893
From: LONG ISLAND
2025 C3 ('68-'73) of the Year Finalist - Unmodified
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I’ve been around for a long long time.
I was around muscle cars when the first aluminum and fiberglass flex fans first came on the market.
At the time the big selling point was that they reduced weight on the crank because they eliminated the heavy clutches and in doing so they would allow the engine to rev faster.
Better cooling wasn’t their purpose, but since the clutches were eliminated the flexibility of the fan blades was to replace the function of the clutch.
Back then another selling point of the flex fans was that the factory fan clutches had a higher rate of failure than today’s and the with a flex fan the clutch was eliminated so you never had to worry about the clutch failing.
They were a big hit with the motor home owners.
They worked well, but over the years the quality went down hill and there were reports of the blades coming apart, even more so today.
The new clutches are more improved, last for decades and are somewhat lighter weight than the early clutches.
Now electric fans are all the rage and in my opinion a big improvement over the clutch fans, depending on the application.
In a stock or mildly built engine like the OP’s I would run a clutch fan set up before electric fans.
In a high performance engine where cooling is essential at slow speeds, electric fans are my choice.
Now in my older Jeep and the way I use it the clutch fan set up is way better than an electric fan set up.
If the OP’s car was mine I would use the clutch and fan set up, but it isn’t my car.
The last thing I would use would be a flex fan.
I was around muscle cars when the first aluminum and fiberglass flex fans first came on the market.
At the time the big selling point was that they reduced weight on the crank because they eliminated the heavy clutches and in doing so they would allow the engine to rev faster.
Better cooling wasn’t their purpose, but since the clutches were eliminated the flexibility of the fan blades was to replace the function of the clutch.
Back then another selling point of the flex fans was that the factory fan clutches had a higher rate of failure than today’s and the with a flex fan the clutch was eliminated so you never had to worry about the clutch failing.
They were a big hit with the motor home owners.
They worked well, but over the years the quality went down hill and there were reports of the blades coming apart, even more so today.
The new clutches are more improved, last for decades and are somewhat lighter weight than the early clutches.
Now electric fans are all the rage and in my opinion a big improvement over the clutch fans, depending on the application.
In a stock or mildly built engine like the OP’s I would run a clutch fan set up before electric fans.
In a high performance engine where cooling is essential at slow speeds, electric fans are my choice.
Now in my older Jeep and the way I use it the clutch fan set up is way better than an electric fan set up.
If the OP’s car was mine I would use the clutch and fan set up, but it isn’t my car.
The last thing I would use would be a flex fan.
I Couldn't have said any it better myself !!
Melting Slicks
Joined: Apr 2021
Posts: 2,661
Likes: 2,118
From: Minnesota
I feel like they don't use the most power honestly. They're designed to flatten out at higher rpms to reduce drag on the engine. A clutch fan is always engaged. The drag only increases with engine speed for those.
as for durability, youre probably right. I did get a really well built one that's stainless steel construction so maybe it won't be so bad
as for durability, youre probably right. I did get a really well built one that's stainless steel construction so maybe it won't be so bad
Flex fans on the other hand…
Race Director
Joined: Nov 2006
Posts: 13,177
Likes: 7,781
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
I run factory C5 Corvette twin electric fans in my C3. With a very well sorted upgraded electrical/charging system.
Fans never need to run when moving. And really cool down the engine when stopped at a long light.
And no blades flying through the hood!
Seriously, there have been numerous dyno tests done and published as per power loss with different fans.
The flex fan is the clear losser.
Fans never need to run when moving. And really cool down the engine when stopped at a long light.
And no blades flying through the hood!
Seriously, there have been numerous dyno tests done and published as per power loss with different fans.
The flex fan is the clear losser.
Drifting
Joined: May 2020
Posts: 1,663
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From: Baton Rouge, Louisiana, metro area
Engine Masters did an episode on fans a while back. Whether you like the show or not, it was still an interesting episode (S2E2).
They tested hp effect. They did not specifically test the effect on cooling ability; however, I would think drain on hp would correlate to movement of air.
The factory, rigid mount steel blade and plastic/fiberglass flex fan drained the most hp which indicates, to me, they moved most air.
The factory clutch fan drew down a little less hp.
The aluminum flex fan pulled down very little hp. Indicates the flex doesn’t move as much air.
None of the three were supportive of the flex fans.
I personally have dual Jegs electric fans on my stock L48 with aluminum radiator. They were a lot of work fabricating mounting brackets and wiring control wiring, but they work great and give lots of room in the front of the engine. A little noisy, but not too bad.
They tested hp effect. They did not specifically test the effect on cooling ability; however, I would think drain on hp would correlate to movement of air.
The factory, rigid mount steel blade and plastic/fiberglass flex fan drained the most hp which indicates, to me, they moved most air.
The factory clutch fan drew down a little less hp.
The aluminum flex fan pulled down very little hp. Indicates the flex doesn’t move as much air.
None of the three were supportive of the flex fans.
I personally have dual Jegs electric fans on my stock L48 with aluminum radiator. They were a lot of work fabricating mounting brackets and wiring control wiring, but they work great and give lots of room in the front of the engine. A little noisy, but not too bad.
Race Director
Joined: Nov 2006
Posts: 13,177
Likes: 7,781
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
The mechanical fans pull down a lot of power at higher RPM's. Unfortunately, that's not when we need a fan.
We need fans to cool the radiator when not moving or moving very slowly. Generally, engine RPM's are realitivly low in these situations.
So H.P. loss doesn't necessarily mean better fan efficiency.
Electric fans spin at full speed (if necessary) at idle. Mechanical fans turn at low speed at idle. (When you need them the most) and the flex fan may flatten out at RPM. And that does help some. But it's still robing HP and fuel economy all the way down the highway.
We need fans to cool the radiator when not moving or moving very slowly. Generally, engine RPM's are realitivly low in these situations.
So H.P. loss doesn't necessarily mean better fan efficiency.
Electric fans spin at full speed (if necessary) at idle. Mechanical fans turn at low speed at idle. (When you need them the most) and the flex fan may flatten out at RPM. And that does help some. But it's still robing HP and fuel economy all the way down the highway.
Drifting
Joined: May 2020
Posts: 1,663
Likes: 702
From: Baton Rouge, Louisiana, metro area
The mechanical fans pull down a lot of power at higher RPM's. Unfortunately, that's not when we need a fan.
We need fans to cool the radiator when not moving or moving very slowly. Generally, engine RPM's are realitivly low in these situations.
So H.P. loss doesn't necessarily mean better fan efficiency.
Electric fans spin at full speed (if necessary) at idle. Mechanical fans turn at low speed at idle. (When you need them the most) and the flex fan may flatten out at RPM. And that does help some. But it's still robing HP and fuel economy all the way down the highway.
We need fans to cool the radiator when not moving or moving very slowly. Generally, engine RPM's are realitivly low in these situations.
So H.P. loss doesn't necessarily mean better fan efficiency.
Electric fans spin at full speed (if necessary) at idle. Mechanical fans turn at low speed at idle. (When you need them the most) and the flex fan may flatten out at RPM. And that does help some. But it's still robing HP and fuel economy all the way down the highway.
Completely agree with everything you list above. The EM show study did not address cooling or efficiency - only hp loss at various speeds. I am making the assumption that hp loss is related to volume of air moved/cfms/heat transfer ability/etc, since the loss is from drag on the engine.
Assuming I am correct, the results of the show are consistent with your statements that the flex fan does not move as much air and would likely not generate equal heat transfer at any rpm as the factory fans. This difference can vary over rpm’s since the flex changes shape depending on speed while the factory fans do not.
So the question would be whether the flex would move enough air at low rpm’s to cool the engine since high speed movement is not a problem.
If I were going with a flex fan, I would select one with a pitch and blade size as close to the factory fans as possible thereby getting as much air at low speed, before it deforms. As 4-Vette’s stated, that is where you need it. In the EM study, the plastic flex fan seemed to be the closest in original shape as the factory, and, based on hp loss comparison, performed closer to the factory fan than the metal flex fan.
(I would still go with dual electric fans, if it were mine.)
d
Race Director
Joined: Jun 2000
Posts: 10,039
Likes: 669
From: FL
From an old post.
Car Craft May 2000, page 50 and 51. Dyno test. Max power:
alternator, no fan 496 hp
plastic flexfan 460 hp
low-profile flexfan 466 hp
hi-perf flexfan 476 hp
6-blade rigid fan 449 hp
4-blade ridid fan 473 hp
HD thermal clutch fan 476 hp
thermal clutch fan 487 hp
non-thermal clutch fan 485 hp
alternator, electric fan 494 hp
Car Craft May 2000, page 50 and 51. Dyno test. Max power:
alternator, no fan 496 hp
plastic flexfan 460 hp
low-profile flexfan 466 hp
hi-perf flexfan 476 hp
6-blade rigid fan 449 hp
4-blade ridid fan 473 hp
HD thermal clutch fan 476 hp
thermal clutch fan 487 hp
non-thermal clutch fan 485 hp
alternator, electric fan 494 hp
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