What's the deal with fan types? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lngbed71 · 02-23-2007, 10:24 AM

As of late I've browsed across posts about how bad flex fans are, and how they break and mess up everything under the hood. I don't get it, I've run them as long as I can remember and have never had anything go wrong with them. I have read where the "flex" part of them will fatigue and break over repeated flexing and such, but again I haven't heard of or experienced anything like that. Is there something I'm missing or is it because I getting "aged"? Are there any articles and what-not about the safety of these flex fans someone can refer me to? Any help appreciated, thanks
JK

**Yukon Jack** · 02-23-2007, 10:28 AM

There is a recent post here that shows the gaping hole that resulted in a boardmember's hood from a flex fan letting go. That, and reading a local newspaper article a couple years ago about a man who was killed when his flex fan came apart is all the proof I need to know I won't ever use one.

67cruiser · 02-23-2007, 10:48 AM

Look back at "Mr Magoo" post on 2/06/07. Don't know how to move thread to this post.

MR MAGOO · 02-23-2007, 10:58 AM

My Flex Fan Was About 8 Years Old When It Let Go.

jacobs · 02-23-2007, 11:02 AM

I'm sure engine rpm's and water pump pulley sizes has a lot to do with flex fans coming apart. I doubt I would have any problems with them.....however, 30 years ago....now that's a different story!

Bowtie001 · 02-23-2007, 11:31 AM

I've never run them - so take this with a grain of salt. Flex fans are power hungry - carcraft or hotrod found 20 hp at the wheels through different fans I think. Big flex fans were worst, clutch fans were great, and electric has obvious benefits.

As far as coming apart - the engineer in me says: Since aluminum has a finite fatigue life, it stands to reason that at some point they will fail. Unlike steel - the more you flex aluminum the weaker it gets. If we can assume one flex = slowing down or speeding up (shifting, merging etc) I would guess something like 20-50 flexes per trip, round trip would be double that so we'll make it an even 100. Assume one round trip per day for 8 years and we get 291,200 flexes. That's significant, as fatigue life is usually considered infinite when 1 million cycles are reached. I would suspect that some of the metallurgy in these cheapo auto-store flex fans would be even worse. It sounds possible, and no, it doesn't matter how big they make it... if it flexes and is aluminum it will fail eventually. That's why they have to decommission airplanes after too many hours.

Just my opinion though - I am far from an experienced metallurgist. Go with a clutch fan and save some power/gas/noise in th process.
-Brian

**Zoomad75** · 02-23-2007, 11:43 AM

Wow that's a pretty nasty hole in the hood. I'm looking at it this way, if it can tear through the heavy sheetmetal of a 67-72 truck it's going to do a heck of a lot more damage to a human leaning over to tweak the carb or other adjustments when the engine is running.

I've always run clutch fans on my junk. Yeah they can be big and ugly but my K5 runs very cool in the summer with it. Plus the chances of it coming apart are a heck of a lot less. Way I see it, GM must have had a reason not to use the aftermarket style flex fan. A 5 or 7 blade fan with a clutch and the correct fan shroud is hard to beat.

Bowtie001 · 02-23-2007, 11:46 AM

Plus, big and ugly rocks. Function before Form and all that jazz.
-Brian

**special-K** · 02-23-2007, 12:17 PM

I`ve never had a problem in my years,either.I thought they were stainless not aluminum.That fan must have been so deteriorated and off balance that part of the steel center came apart with it.Like it ripped off the bolt hub.It`s hard to understand how a piece of thin flimsy stock could tear through the much heavier metal in one of our hoods.Say what you will,I`d just like to know more about the fan.

*Shane* · 02-23-2007, 12:24 PM

Why even take the chance when there are safer & better alternatives available?

Bowtie001 · 02-23-2007, 12:24 PM

SpecialK,
Just did some research, turns out the better ones are stainless, so my fault on that one. Some of them are aluminum though - and I guess we won't know much about the ones that were the subject of horror stories.

My guess on why the fan went through the hood would be based on speed and luck. It hit the un-reinforced part of the hood in that one pic, and the fan blades are going ~70 mph at 4 grand. I could put an egg through the hood if you give me a big enough gun.

Just an opinion though - I have never had exp with flex fans as I said earlier, it's all just math at this point.

-Brian

FLEET72 · 02-23-2007, 12:46 PM

Quote:

Originally Posted by special-K

I`ve never had a problem in my years,either.I thought they were stainless not aluminum.That fan must have been so deteriorated and off balance that part of the steel center came apart with it.Like it ripped off the bolt hub.It`s hard to understand how a piece of thin flimsy stock could tear through the much heavier metal in one of our hoods.Say what you will,I`d just like to know more about the fan.

These pictures were taken of my '89 S-10 that has a 2.5l 4banger under the hood. The fan was PLASTIC and clutch mounted and it took out the hood, shroud and bent the lower splash pan under the truck. That happened 3 years ago and since I didn't want to sink money into the truck I just hammered the hole closed(somewhat) and squirted some paint on it. I was going to get a new hood someday but that never came.

sneakysnake · 02-23-2007, 02:25 PM

I had a buddy's truck that we had just been working on and leaning over the motor and fan not ten minutes earlier come apart and hit the hood like those above. Now you cant get me lean over the fan.Long ago I was putting one on with an air ratchet and there was no belt on the pulley, well lets just say when the bolt got tight I nearly lost a knuckle when the blade came around and sliced a big hunk out of it, but I'm much smarter now.LOL

hvychve · 02-23-2007, 02:30 PM

I had a good experience witha flex fan, but I also have heard for many years of there blades coming apart , being extremely dangerous, I dont use one for that reason,
many years ago, I was working on a v-8 vega of a customers, he had no shroud , I leaned over to snap the throttle with my right hand, I went to brace myself with my left hand on the shroud, but there was no shroud, I grabbed the fan, I quickly pulled back to look at how many fingers were gone, I couldnt believe my eyes, they were all there, but I have scars that run across four fingers at the knuckles, I was lucky it was a flex fan, if it werent for the give in the blades, I think I would have only a pinky and a thumb today. I am not recomending sticing your hand into a flex fan, or any fan for that matter, I just figured I got lucky that day, I use a clutch fan. just a word of thought , dont try this at home!

**special-K** · 02-23-2007, 02:43 PM

Whoa!Close call,alright.With the hood slice thing,stranger things have been known to happen.Like,straw into wood in a tornado.I don`t have anything with a flex-fan now.The fact that it`s been proven they hurt hp is enough for me to not bother with them.

Bowtie001 · 02-23-2007, 02:51 PM

Wow, I am glad you guys have all of your appendages. I actually put a clutch fan through my radiator before.

It was completely my fault, and I am very

for doing it. let's just say that the bolts weren't tight... and that's being kind.

The populace has spoken. Now go get an electric fan. Teehehee j/k

P.S. sneakysnake - gotta love the motto below your name, I'll use that on the wife next time.

-Brian

CUSTOM 72 · 02-23-2007, 03:20 PM

I Got Rid Of Mine And Installed A Twin Electric Fan Set Out Of A Lexus. Wired To The Ignition For Now So It Runs All The Time. But Man Dose It Keep The Engine Sool. I Have Seen The Damage The A Flex Fan Can Do, Not Something I Want To See Again.

fastwillie 696969 · 02-23-2007, 03:32 PM

they make good throwing star for ninja's

Longhorn Man · 02-23-2007, 03:51 PM

GM had a recall on factory flex fans, they are bad news.
They flex a whole lot more than one would think. Once you are reved at about 2000 RPM, the fan is almost flat, figure how often you rev between 1500 to 2000+... it's a whole bunch.
I've seen the fan blades go through the spine of a hood, so it isn't just the sheet metal that it'll go through.
Custom72, I wouold hurry up and wire those fans properly. If they are on all the time, not only are you putting years upon years of wear on them, but you are also taxing your charging system.

02-23-2007, 10:24 AM	#1
lngbed71 Nothing fits but the oil Join Date: Mar 2003 Location: Gaston, Indiana Posts: 424	What's the deal with fan types? As of late I've browsed across posts about how bad flex fans are, and how they break and mess up everything under the hood. I don't get it, I've run them as long as I can remember and have never had anything go wrong with them. I have read where the "flex" part of them will fatigue and break over repeated flexing and such, but again I haven't heard of or experienced anything like that. Is there something I'm missing or is it because I getting "aged"? Are there any articles and what-not about the safety of these flex fans someone can refer me to? Any help appreciated, thanks JK __________________ Land of the free Because of the brave

02-23-2007, 10:28 AM	#2
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,684	Re: What's the deal with fan types? There is a recent post here that shows the gaping hole that resulted in a boardmember's hood from a flex fan letting go. That, and reading a local newspaper article a couple years ago about a man who was killed when his flex fan came apart is all the proof I need to know I won't ever use one. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

02-23-2007, 10:48 AM	#3
67cruiser Registered User Join Date: Dec 2006 Location: OKLAHOMA Posts: 140	Re: What's the deal with fan types? Look back at "Mr Magoo" post on 2/06/07. Don't know how to move thread to this post. __________________ 67 C10 SWB 350-Turbo 400 tranny-Disc brake "Those who live by the sword get shot by those who don't"

02-23-2007, 10:58 AM	#4
MR MAGOO Registered User Join Date: Jan 2007 Location: minden la Posts: 80	Re: What's the deal with fan types? My Flex Fan Was About 8 Years Old When It Let Go. Attached Images __________________ 1972 C-10 SWB 350CI TURBO 350 TRANNY, TILT, POWER WINDOW & BRAKES, TANK UNDER THE BED W/MARKER LIGHT FILLER. 3.08 GEARS, CLASSIC AIR :hit2: :hit2: 4 WHEEL DISK BRAKES 2000 chevy blazer 1990 nissan pick-up 1984 mazda pick-up (son's project truck)

02-23-2007, 11:02 AM	#5
jacobs Registered User Join Date: Sep 2005 Location: 9000' Mountain Man Posts: 326	Re: What's the deal with fan types? I'm sure engine rpm's and water pump pulley sizes has a lot to do with flex fans coming apart. I doubt I would have any problems with them.....however, 30 years ago....now that's a different story!

02-23-2007, 11:31 AM	#6
Bowtie001 Project underway - finally. Join Date: Feb 2007 Location: Greenville, SC Posts: 493	Re: What's the deal with fan types? I've never run them - so take this with a grain of salt. Flex fans are power hungry - carcraft or hotrod found 20 hp at the wheels through different fans I think. Big flex fans were worst, clutch fans were great, and electric has obvious benefits. As far as coming apart - the engineer in me says: Since aluminum has a finite fatigue life, it stands to reason that at some point they will fail. Unlike steel - the more you flex aluminum the weaker it gets. If we can assume one flex = slowing down or speeding up (shifting, merging etc) I would guess something like 20-50 flexes per trip, round trip would be double that so we'll make it an even 100. Assume one round trip per day for 8 years and we get 291,200 flexes. That's significant, as fatigue life is usually considered infinite when 1 million cycles are reached. I would suspect that some of the metallurgy in these cheapo auto-store flex fans would be even worse. It sounds possible, and no, it doesn't matter how big they make it... if it flexes and is aluminum it will fail eventually. That's why they have to decommission airplanes after too many hours. Just my opinion though - I am far from an experienced metallurgist. Go with a clutch fan and save some power/gas/noise in th process. -Brian __________________ 1972 GMC Pre-resto... awaiting allocated funding.

02-23-2007, 11:43 AM	#7
Zoomad75 K5Camper Join Date: Mar 2004 Location: Pueblo, CO Posts: 1,513	Re: What's the deal with fan types? Wow that's a pretty nasty hole in the hood. I'm looking at it this way, if it can tear through the heavy sheetmetal of a 67-72 truck it's going to do a heck of a lot more damage to a human leaning over to tweak the carb or other adjustments when the engine is running. I've always run clutch fans on my junk. Yeah they can be big and ugly but my K5 runs very cool in the summer with it. Plus the chances of it coming apart are a heck of a lot less. Way I see it, GM must have had a reason not to use the aftermarket style flex fan. A 5 or 7 blade fan with a clutch and the correct fan shroud is hard to beat. __________________ Rob Z. 1975 K5 350/465/205/D44/12b 4" lift on 35's- RIP 1991 K5 8.1L/NV4500/241/D44/14b FWC Camper

02-23-2007, 11:46 AM	#8
Bowtie001 Project underway - finally. Join Date: Feb 2007 Location: Greenville, SC Posts: 493	Re: What's the deal with fan types? Plus, big and ugly rocks. Function before Form and all that jazz. -Brian __________________ 1972 GMC Pre-resto... awaiting allocated funding.

02-23-2007, 12:17 PM	#9
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,852	Re: What's the deal with fan types? I`ve never had a problem in my years,either.I thought they were stainless not aluminum.That fan must have been so deteriorated and off balance that part of the steel center came apart with it.Like it ripped off the bolt hub.It`s hard to understand how a piece of thin flimsy stock could tear through the much heavier metal in one of our hoods.Say what you will,I`d just like to know more about the fan. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

02-23-2007, 12:24 PM	#10
Shane Account Suspended Join Date: Jun 2000 Location: over yonder Posts: 14,270	Re: What's the deal with fan types? Why even take the chance when there are safer & better alternatives available? Last edited by Shane; 02-23-2007 at 12:26 PM.

02-23-2007, 02:25 PM	#13
sneakysnake It's a catastrophic success. Join Date: Jan 2003 Location: Oklahoma Posts: 2,077	Re: What's the deal with fan types? I had a buddy's truck that we had just been working on and leaning over the motor and fan not ten minutes earlier come apart and hit the hood like those above. Now you cant get me lean over the fan.Long ago I was putting one on with an air ratchet and there was no belt on the pulley, well lets just say when the bolt got tight I nearly lost a knuckle when the blade came around and sliced a big hunk out of it, but I'm much smarter now.LOL

02-23-2007, 02:30 PM	#14
hvychve To The Levy Join Date: Jan 2007 Location: california Posts: 391	Re: What's the deal with fan types? I had a good experience witha flex fan, but I also have heard for many years of there blades coming apart , being extremely dangerous, I dont use one for that reason, many years ago, I was working on a v-8 vega of a customers, he had no shroud , I leaned over to snap the throttle with my right hand, I went to brace myself with my left hand on the shroud, but there was no shroud, I grabbed the fan, I quickly pulled back to look at how many fingers were gone, I couldnt believe my eyes, they were all there, but I have scars that run across four fingers at the knuckles, I was lucky it was a flex fan, if it werent for the give in the blades, I think I would have only a pinky and a thumb today. I am not recomending sticing your hand into a flex fan, or any fan for that matter, I just figured I got lucky that day, I use a clutch fan. just a word of thought , dont try this at home!

02-23-2007, 02:43 PM	#15
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,852	Re: What's the deal with fan types? Whoa!Close call,alright.With the hood slice thing,stranger things have been known to happen.Like,straw into wood in a tornado.I don`t have anything with a flex-fan now.The fact that it`s been proven they hurt hp is enough for me to not bother with them. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

02-23-2007, 02:51 PM	#16
Bowtie001 Project underway - finally. Join Date: Feb 2007 Location: Greenville, SC Posts: 493	Re: What's the deal with fan types? Wow, I am glad you guys have all of your appendages. I actually put a clutch fan through my radiator before. It was completely my fault, and I am very for doing it. let's just say that the bolts weren't tight... and that's being kind. The populace has spoken. Now go get an electric fan. Teehehee j/k P.S. sneakysnake - gotta love the motto below your name, I'll use that on the wife next time. -Brian __________________ 1972 GMC Pre-resto... awaiting allocated funding.

02-23-2007, 03:20 PM	#17
CUSTOM 72 Registered User Join Date: Feb 2007 Location: winfield bc Posts: 54	Re: What's the deal with fan types? I Got Rid Of Mine And Installed A Twin Electric Fan Set Out Of A Lexus. Wired To The Ignition For Now So It Runs All The Time. But Man Dose It Keep The Engine Sool. I Have Seen The Damage The A Flex Fan Can Do, Not Something I Want To See Again. __________________ 1972 c/10 Custom, Long Box, 350 Small Block, Auto 3 Speed, Custom Wood box, Full Air Ride, 3" C-Notch, 20" Front & 22" Rear Tires, Snow White Paint, PT Crusher Handles,



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02-23-2007, 03:32 PM	#18
fastwillie 696969 ~Rest In Peace~ Join Date: May 2005 Location: CALIFORNIA NOR CAL Posts: 9,707	Re: What's the deal with fan types? they make good throwing star for ninja's __________________ is it fast ? it has a lighting bolt donut? B___H please, I can remove 90% of your so called "beauty" with a kleenex

02-23-2007, 03:51 PM	#19
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: What's the deal with fan types? GM had a recall on factory flex fans, they are bad news. They flex a whole lot more than one would think. Once you are reved at about 2000 RPM, the fan is almost flat, figure how often you rev between 1500 to 2000+... it's a whole bunch. I've seen the fan blades go through the spine of a hood, so it isn't just the sheet metal that it'll go through. Custom72, I wouold hurry up and wire those fans properly. If they are on all the time, not only are you putting years upon years of wear on them, but you are also taxing your charging system.

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