Flex Fan vs Clutch Fan

[67Slider]

OK; I have wondered for awhile but never thought to ask. What are the pros and cons of flex fans vs clutch fans?

[6772owner]

After my personal experience with my 67' K10 I would say to go for the regular clutch fan. The flex fan was not able to pull the CFM I needed to keep the engine cool. The flex fan is "running" all the time (and sucking power all the time) were the clutch is able to engage/disengage based on the temperature. The flex fan is called a "flex" fan because the blades are supposed to flex and cause less drag, but they are also not pulling much air when "flattened" out. I will never use a flex fan (and never have, the PO had installed this one)

Just my $.02

[Sinister]

The metal flex fans have been known to come apart and go through the hood. That said I'm running a nylon flex fan and it keeps things at a steady 190*. If I wasn't running this successfully I'd run a clutch fan.

[Shane]

the only thing a flex fan is good for is putting blade-shaped holes in your hood when it flies apart.

[FlounderGDI]

I was just told by my engine builder the other day that he always recommends the clutch fan. He was telling me at the higher RPMs that the flex fan blades flatten out and quit pulling air and essentially block the air from moving through the radiator.

[marks1972]

Originally Posted by FlounderGDI

I was just told by my engine builder the other day that he always recommends the clutch fan. He was telling me at the higher RPMs that the flex fan blades flatten out and quit pulling air and essentially block the air from moving through the radiator.

i heard the same thing.

[Shyguy]

Years ago I tried a flex fan on my '92 K-3500 with a 454 and was real disappointed because it did not keep the engine as cool as the stock fan with clutch setup.

The flex fan is now a wall ornament in my garage and will always be.

[turp mcspray]

Several years ago, one of the magazines did a dyno test of several differant fans. The clutch fan was the hands down winner in airflow, as well as horsepower loss.

[Stocker]

In 33 years, I have never overheated with a clutch fan. But one time the silicon fluid had somehow become depleted, so I temporarily put a flex fan on. The truck ran hot. I sold the flex fan for a half-rack of Bud.

[Bad70sbchevy]

I guess I'll have to be different. I have a flex fan on my truck and that thing can pull some air. My engine barely gets above cold even on the hottest florida afternoons stuck in 5:00 traffic. Mine can definitely move more air than any clutch fan. Yes, they do flatten out at high rpms but unless your turning 5000rpm, it will still pull air. The only complaints I hear is if they come apart they can do some damage but even a regular fan can do that. I looked at mine and it looks pretty stout. Thats just my two cents.

[Hubscrub]

and a flex fan will cut the crap out of you if your working near it i loseing mine ASAP

[72lb4x4]

One of the more prominent and funny people on this site once posted an answer to a similar question that I'll paraphrase: A cluch fan won't fly apart and try to kill you like a flex fan.

[El Jay]

Originally Posted by Shane

the only thing a flex fan is good for is putting blade-shaped holes in your hood when it flies apart.

X 2 ^

But, I've often wondered, why don't they ever seem to go downward when they fail?
Maybe nobody talks about those failures.

[Bad70sbchevy]

Let me just throw this out there. I don't think there really isn't any difference from a performace standpoint. A clutch fan and a flex fan (just thinking out loud, tell me if I'm wrong) generate a constant cfm throughout the rpm band. A clutch fan will continue to turn faster until a certain rpm and then hold there by allowing to fan to slip. A flex fan accomplishes this instead by flattening out gradually, but at the same time its turning faster thus producing a constant flow of air (cfm). The only real difference is at idle where the flex fan has a much more aggresive angle pulling more air than a clutch fan, but it all depend on what kind of fan you have attached to the clutch (it can happen vise versa). The only con with a flex fan is like everyone else is sayin, that is one thing you do not want to get your arm caught in. If your really wantin the best fan, I would probably go electric because they dont have to run all the time, just come on when needed freein up some extra horsepower and gas mileage without sacrificing cooling.

[Buford]

I just replaced my fan clutch with a new thermal clutch and it works great. I was driving around today (around 95 degrees) and the truck cruised at 180 with the A/C on (I have a 180 thermostat). My only word of caution is make sure you get a thermal clutch fan and not the non-thermal clutch fan. You will have a higher chance of overheating at idle with a non-thermal because it responds to rpm versus temperature. Good luck!

[ERASER5]

Originally Posted by Sinister

The metal flex fans have been known to come apart and go through the hood. That said I'm running a nylon flex fan and it keeps things at a steady 190*. If I wasn't running this successfully I'd run a clutch fan.

The nylon fan from Flex-a-lite is what I have on 2 different motors. They WILL move air! So much that when I get above 3000 rpm, the fan will slow the WP pulley and make the belt squeal. I have to get the belt tension just right. The engine never gets hot, the fan will not explode, and are not sharp edged. I installed the first one in the mid '80s. A guy running dirt track racing put me on to them.

Once I upgrade my alt to 100+ amps, I am going to install an electric fan. I am positive that my plastic fan is using some HP.

[storm9c1]

I'm a fan of clutch fans.

When they are working properly, I like how they will engage when hot and disengage to 20% when cool. Makes perfect sense to me and you can use a deep pitched fan with the HD or Severe Duty clutches. A deep pitched fan will really move some air. And when it's not needed (and thermally cuts out), I can't see how it would rob too much power unless the wrong clutch is used or the engine constantly runs super hot.

I recently posted a reply to another related question. I discussed the different fan clutches:

http://67-72chevytrucks.com/vboard/s...d.php?t=412494

[68K30]

I put a used, stock GM flex fan on my 454 in my 68, it threw a blade on the first trip on the new water pump/GM fan. The old water pump had a 1970 AMC flex fan that I put on when I installed the engine, [could not remember where I put the GM fan] never had any trouble with that fan or any other AMC flex fan on several AMC's [Mark Donahue Javelin,Rebel Machine]. Replaced the broken fan with a Flex-a-lite SFI approved flex fan,works great. By the way the blade that detached went downward,. cut the steering return hose and put a nice gouge in my frame.

Bill

[bigsnookmaster]

Originally Posted by Bad70sbchevy

I guess I'll have to be different. I have a flex fan on my truck and that thing can pull some air. My engine barely gets above cold even on the hottest florida afternoons stuck in 5:00 traffic. Mine can definitely move more air than any clutch fan. Yes, they do flatten out at high rpms but unless your turning 5000rpm, it will still pull air. The only complaints I hear is if they come apart they can do some damage but even a regular fan can do that. I looked at mine and it looks pretty stout. Thats just my two cents.

I've also had good luck with flex fans. Good ones with stainless steel blades from NAPA, and I think quality has something to do with the ones that fly apart, I have also seen the holes through the hood before. I run dual 13.5" Flex-a-lite fans now, with no problems at all.

[C10-Driver]

^^ I agree ^^

I am also running a Flex-a-lite fan on my truck and on a 100 degree day, idling with the A/C on, my truck doesn't get over 180 degrees. I also run my small block up to 6000 RPM on occaison and haven't had any problems.

[mrein3]

Way back before Al Gore invented the internet, I went to look at a 1971 Chevelle convertible. I test drove it before I opened the hood. Right when I started it I wondered WTF is making all that noise under the hood. It sounded like crap. When I got out of sight of the owner I popped the hood to see what was making all that noise. It was a flex fan. That was the first time I ever heard of or saw one.

THE VERY FIRST THING I DID after I purchased it was replace the flex fan with a factory clutch fan setup that I procured from one of the many 70, 71, and 72 Chevelles that were rusted apart around here and sitting in bone yards.

After our boy Al Gore invented the internet I read about how they don't move the air like a factory fan and got to see pictures of what happens when one of those flex fans comes apart.
Scroll down to #17 in this one:
http://67-72chevytrucks.com/vboard/s...d.php?t=339130

So in summary, they sound like crap, move questionable air, can maim you, and/or can poke holes in your sheet metal. Stick with your OEM clutch fan setup.

[eightbanger]

This is how hood louvres started