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#1 |
Registered User
Join Date: Mar 2010
Location: Pueblo West, CO
Posts: 944
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Flex Fan vs Clutch Fan
OK; I have wondered for awhile but never thought to ask. What are the pros and cons of flex fans vs clutch fans?
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67 C10 Stepside 66 Mustang Coupe 99 Burb 2500 |
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#2 |
Gearhead
Join Date: Jan 2008
Location: Colorado
Posts: 1,193
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Re: Flex Fan vs Clutch Fan
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
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2002 Saturn SL2, My D/D 2019 Ford Fusion SE, Ecoboost - Wife's D/D 1993 Camaro Z28, A4, CAI, Cat-Back Exhaust Project C10 (my 72' C10 w/96' LT1, 700R4, bagged F&R, 18's (for now), Short/Fleet) -- SOLD! Build Thread: http://67-72chevytrucks.com/vboard/s...d.php?t=313644 |
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#3 |
Between Trucks...
Join Date: Mar 2002
Location: Los Angeles, CA.
Posts: 3,830
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Re: Flex Fan vs Clutch Fan
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.
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#4 | |
Registered User
Join Date: Jun 2006
Location: Indiana
Posts: 4,859
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Re: Flex Fan vs Clutch Fan
Quote:
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.
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'70 GMC C1500 LWB Power disc brakes. WooHoo! Posi 6 Lug Dana 60 |
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#5 |
*** That's interesting ***
Join Date: Oct 2008
Location: Pittsburgh, PA
Posts: 2,772
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Re: Flex Fan vs Clutch Fan
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
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Tom ![]() Chevy by day... 1969 Chevy C30 Rollback Tow Truck -- 383 stroker, 4L80E 2011 Chevy Caprice PPV 9C3 6.0L 1995 Chevy Caprice 9C1 1994 Chevy Caprice 9C1 #3 1995 Chevy Caprice Wagon #2 1995 Chevy Impala SS Mopar by night... 1969 Dodge Charger 1972 Chrysler Newport 2dr Hardtop (27K miles) Plus others... |
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#6 |
Registered User
Join Date: May 2007
Location: Pennsylvania
Posts: 99
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Re: Flex Fan vs Clutch Fan
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 Last edited by 68K30; 07-21-2010 at 11:09 PM. |
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#7 |
Account Suspended
Join Date: Jun 2000
Location: over yonder
Posts: 14,270
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Re: Flex Fan vs Clutch Fan
the only thing a flex fan is good for is putting blade-shaped holes in your hood when it flies apart.
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#8 |
Registered User
Join Date: Sep 2009
Location: Lafayette, Indiana
Posts: 339
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Re: Flex Fan vs Clutch Fan
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.
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1969 CST/10 "GreenAndWhite" 1974 Nova (SOLD... End of an Era) 2000 Impala (RIP) 2008 Malibu Brand Loyal... I've never owned a Vehicle not made by Chevrolet. |
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#9 |
Registered User
Join Date: May 2010
Location: Atoka, TN
Posts: 240
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Re: Flex Fan vs Clutch Fan
i heard the same thing.
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Mark ![]() 1968 C-10 SWB 307/munci 4spd/411possi 1986-1990 1972 Cheyenne-10 LWB 350/TH350 ![]() U. S. Navy Seabee "CAN DO", "The difficult we do at once. The impossible may take a little bit longer.","We Build We Fight", "Work Hard Play Hard" |
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#10 | |
Gone to greener pastures
![]() Join Date: May 2007
Location: Gateway to the Delta
Posts: 7,354
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Re: Flex Fan vs Clutch Fan
Quote:
But, I've often wondered, why don't they ever seem to go downward when they fail? Maybe nobody talks about those failures.
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'69 Chevy 1/2 T LWB Stepper: Daily Beater '72 GMC 3/4 T Fleet: Another Daily Beater '72 Plymouth Gran Coupe: ? "Ah women. They make the highs higher and the lows more frequent." Friedrich Nietzsche "Never kick a fresh turd on a hot day." Harry S. Truman GUN CONTROL: Never having to say, "I missed you." Always fire two warning shots into your attacker's chest area before putting a bullet between his eyes. Paraphrased from Louis Awerbuck |
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#11 |
Junior Member
Join Date: Dec 2006
Location: Southeast Missouri
Posts: 2,436
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Re: Flex Fan vs Clutch Fan
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.
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'67 Chevy C-20 short stepper - build complete, 454/SM-465. '75 C-30 Single Cab DRW-350 small block/NP-435. '77 GMC-6500 Dump Truck, 427 Tall Deck. '92 GMC K-3500 Duallie, 454/4L80E. |
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#12 |
Registered User
![]() Join Date: May 2007
Location: Rapid City South Dakota
Posts: 2,359
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Re: Flex Fan vs Clutch Fan
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.
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Turp Mcspray New life for an old 2wd, farm blazer http://67-72chevytrucks.com/vboard/s...d.php?t=505987 My Blazer build http://67-72chevytrucks.com/vboard/s...d.php?t=342299 |
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#13 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,638
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Re: Flex Fan vs Clutch Fan
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.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#14 |
Registered User
Join Date: Aug 2009
Location: Newberry,FL
Posts: 277
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Re: Flex Fan vs Clutch Fan
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.
Last edited by Bad70sbchevy; 07-20-2010 at 11:05 PM. |
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#15 |
Cruzin
Join Date: Dec 2009
Location: on the road
Posts: 2,835
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Re: Flex Fan vs Clutch Fan
and a flex fan will cut the crap out of you if your working near it
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Lime Wife's 67https://www.google.com/url?sa=t&rct=...wZEMODaS2d94u8 Back to the Fifties 59 https://www.google.com/url?sa=t&rct=...NAeStpydfrcj_U Proverbs 3:5,6 "Thanks to the Interstate Highway System, it is now possible to travel across the country from coast to coast without seeing anything."Charles Kuralt In memory of our first baby daughter, daddy and mommy love you. Danica Grace 6/26/14
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#16 | |
Registered User
![]() Join Date: Jan 2008
Location: St.Petersburg,Fl
Posts: 1,267
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Re: Flex Fan vs Clutch Fan
Quote:
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#17 |
Account Suspended
Join Date: Jul 2006
Location: DFW
Posts: 1,427
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Re: Flex Fan vs Clutch Fan
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.
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#18 |
Registered User
Join Date: Aug 2009
Location: Newberry,FL
Posts: 277
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Re: Flex Fan vs Clutch Fan
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
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#19 |
Registered User
Join Date: Apr 2008
Location: Los Angeles, CA
Posts: 27
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Re: Flex Fan vs Clutch Fan
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!
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![]() Buford - 1971 3/4 ton, Custom Camper, 350 Th, 350 SBC. |
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#20 |
Chevy Truck Addict
![]() Join Date: Aug 2006
Location: Kelowna, BC
Posts: 1,176
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Re: Flex Fan vs Clutch Fan
^^ 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.
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. 1970 Chev C/10 SWB, 355 SBC, 700R4, 3.73 Posi, Air Ride (Click to view Build Thread) (SOLD) 1978 Chevy C/10 SWB 1970 Pontiac Lemans . |
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#21 |
Registered User
Join Date: Feb 2000
Location: Center City, MN, USA
Posts: 3,254
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Re: Flex Fan vs Clutch Fan
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.
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'70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN |
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#22 |
454 MAKES IT ROAR
Join Date: Jan 2008
Location: Essex, U.K
Posts: 2,701
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Re: Flex Fan vs Clutch Fan
This is how hood louvres started
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Nigel. An American living in a British body. 1971 Chevy Cheyenne 10 454 "In a time of universal deceit, telling the truth becomes a revolutionary act." - George Orwell "When injustice becomes law, resistance becomes duty" - Thomas Jefferson No more pain. 03.12.60 -- 12.28.10 http://www.youtube.com/Eightbanger |
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