chewy

There has been a problem with flex fans for some time that as far as I know hasn't been fixed. They explode for no good reason with disasterous results.

bigvette1

What brand of fan explodes and has this been driven back to the manufacturer to address. I don't want to run on of these.

Maurice

I have lost my fanbelt at the dragstrip before and the next run was my best ever. I also gained over .2 by removing my A/C belt. This was on my 73 running high 14s from low 15s. Lucky I live close enough to the track I could start my car, run up to 50mph, cut the ignition coast to 20ish, repeat until I got home. The gain can be significant if you loosen your belts at the track as you loose the fan, the water pump, and the alternator if they are running off the same belt.


[Modified by Maurice, 6:45 PM 9/9/2003]

19poncho67

Alot of good info here, especially the dyno test results. Here's another good way to think about this: At idle and low speeds in traffic, a flex fan is fully curved for max air flow, which makes it noisy and it's using a lot of power even if the engine doesn't need it. With a clutch, no matter what the engine or vehicle speed is, if the engine is not hot, it disengages, reducing noise and HP consumption. When the engine is hot, the clutch engages, providing cooling air that the engine needs, which should be the most important consideration unless you are at the strip. With a flex fan, at higher speeds, the blades flatten somewhat, which should decrease the HP draw, plus the air that should be pushing thru the radiator because the car is moving faster helps. The ONLY reason the automakers didn't use a clutch on all vehicles is cost. The overall performance of a clutch fan is better than a flex fan, or no cars would have a clutch fan. The Valiants and Falcons often came with a non-flex, non-clutch fan because of cost and need. Those low-performance engines could work just fine with the 4-blade direct fan.[QA UOTE=Pete79L82;1545074576]Now take that same fan and put a radiator in front of it and watch it stop spinning.
From experieance, not theory, I can tell you that a fan take a LOT of horsepower. Taking a fan blade off the engine will always lower lap times on a race track.

Pete[/QUOTE]

Kacyc3

[/QUOTE]

Guess you didnt notice this thread is 16 years old

derekderek

And you don't understand how a clutch fan works. It's not turn on and off with a switch It's just a slipper clutch and so it doesn't run at full engine rpm

fishslayer143

the conclusion that a fan requires 40 hp to turn is flawed.. your comparison is not under actual conditions...you are testing a stationary motor.. load your dyno on a flatbed trailer and drive it 60 mph with a radiator in front.. you will see there is enough airflow thru radiator to spin that clutch fan with the engine off .. also, a SS flex fan blades flatten above 2500 rpm so they require very little power at higher rpm and are rated for 10,000 rpm.. no street motor will ever destroy one .. In addition, I have a 6ft , 10,000 cfm fan In my shop.. it weighs about 80 pounds and only requires a 4 hp electric motor..to spin it . I disagree completely with your conclusion.. Your A/C uses more hp than a mechanical fan ... just my 2 cents worth

Big2Bird

I had a SS flex fan on my 88 dually. I might have a picture where it went thru the hood, cutting the top radiator hose in half, and stuck out the hood 4". NEVER again.

fishslayer143

This is 2019... things have changed.. I had a factory installed clutch fan do that on my 79 GMC. one ton . ..that was 40 yrs ago .. new SSFlex blade are nearly indestructible . I spin mine regularly 6800 rpm for 9 yrs.. never an issue

domenic tallarita

That's exactly what we did at the strip, loosen the belt for a 13 sec period . No temp problems. I also lost a blade on a trip and removed the fan. Cooled good above about 30 mph without a fan. Was not good in town but it got me to a bone yard where I bought a used fan.

Dom

C6_Racer_X

Holy zombie threads!

This discussion is old enough to have its own driver's license.

I'll only respond to 2019 posts here.
The clutch in a fan clutch doesn't work based on engine temperature. And it never fully engages or fully disengages either. The fan clutch is sensitive to the air temperature in front of the fan blades. If that air is over a certain temperature, a thermal spring in the front of the fan clutch applies pressure and increases the engagement of the fan clutch. If the air cools down below the threshold, the thermal spring releases and the clutch "disengages." For a "standard duty fan clutch" which is appropriate for most C3 engines, "disengaged" is a 20-30% engagement (70% to 80% slip ratio), and "fully engaged" with full tension from the bi-metal thermal spring is 60% to 70% engagement (30% to 40% slip ratio).

When you get up to highway speeds (over 40mph), the air flow through the radiator is high enough (enough volume) that the BTUs applied to any volume of air won't increase the temperature to the threshold temperature for the thermal spring, and the clutch will disengage. It will be slipping 70% to 80%, and what little "engagement" is left won't do much because airflow over the fan will be about the same as the speed/pitch of the fan. In top gear on a manual (4 or 5 speed), it's likely that the air will actually be pushing the fan blades and applying a very small torque to the crankshaft.
Flex fans operate on an entirely different principle. The pitch changes based on the pressure differential between the front and back of the blades. The faster it spins, the greater that pressure differential gets, and the blades flatten, resulting in a lower pitch, and reducing the air flow. They try to design them for a constant airflow above a certain RPM range, the pitch reduction cancels the increased rotational speed.

When driving at highway speeds, flex fans still pull, and still draw HP from the engine. That's because the air flow from the moving vehicle reduces the pressure differential, and the blades curl again, increasing the pitch and drawing more air. A flex fan will likely "consume more HP" at highway speeds or higher than a fixed pitch mechanical fan on a fan clutch. It will also draw additional air through the radiator, and add a bit of aerodynamic driving force, like a propeller, drawing a lower pressure in the fan shroud and even in front of the radiator. They can also "pack more air" under the floor pan and slightly reduce aerodynamic down force, especially toward the center and rear of the car.

The big reason factories don't install flex fan is warranty issues. Flex fans fatigue and fail. Even "modern" flex fans fatigue and fail, and when they fail, it's quite a spectacular failure that can damage a lot of other parts (radiator hoses, radiators, hoods, fan shrouds, even other accessories on the engine).
The laws of physics haven't changed. Metal still fatigues. Flex fans will still eventually crack and fail. They always will do that. Some alloys have been developed with much longer fatigue life, but even the newer alloys should be inspected regularly or just replaced regularly as preventative maintenance.

Haggisbash

I liked the electromagnetically controlled fan clutch fitted to a couple of Italian cars I had. The clutch had a slip ring and a carbon brush on the back of it, this was fed power through a thermostat. When the radiator temp was down, no power to the clutch and the fan freewheeled, when the temp climbed the clutch was engaged making the fan rotate at water pump speed (fan was mounted to the water pump shaft same as most old engines). Nice and quiet at low speed when the temp was down, later models from the same manufacturer had electric fans though. When I first got my C3 I was somewhat disappointed at how noisy the fan was at low speeds (it was fitted with a flex fan) I fitted an original fan and noise was about the same, I have too many other projects to do on the car so considering fitting an electric fan is well down the list.

lars

Engine Masters did an excellent dyno test of fans. Pretty conclusive results. For most applications, use a fan with clutch if you don't want to go electric:
https://www.motortrendondemand.com/d...ut/0_olymz420/


Edit:
I'm being told that my link to the Engine Fan Test does not work... not sure what's going on, since it works every time I click on it... If the link does not work, Google "Engine Masters Cooling Fan Test" and open up the "Engine Masters: Season 2, Episode 20 Cooling Fan Shootout". It shows up as:

https://www.motortrendondemand.com/d...ut/0_olymz420/

427Hotrod

I've run a stainless steel 7 blade flex fan on my car forever. In fact...the first one was made about 1981 and was used on my 427" Camaro. my 427" '57 Chevy and then in the Vette. The only reason it's not there now is because I bought a new one that was shinier because I didn't want to polish it.

It's been regularly spun past 8000 RPM using stock pulleys the whole time. Never had an issue. It's been on there on all my latest dragstrip runs where I'm crossing the line at 8000 RPM and it was there when I ran 200 MPH at the TX Mile.

I had once convinced myself to go electric and had even bought the fans etc. I was on a chassis dyno and decided to test it out. I removed it completely and in back to back testing I saw maybe 4-6 RWHP...and I mean MAYBE because that's not uncommon to see on a run to run variation anyway.

I also tested it at the drag strip by using an electric drive setup to run the water pump and fan. Never could tell a difference. I was actually very surprised....I KNOW there's something there....and I was able to keep the car within .02-.04 hundredths run to run (high 9's@142 MPH at the time)...but it never showed on the timeslip as ET or MPH.

Years ago...I could find .05 hundredths by removing the PS belt off the Camaro.

Attached is a screen shot of a little test drive I took a couple of weeks ago....

There's no doubt electric fans can be an advantage...but if you have enough power...maybe you don't notice it. I'll also say that in the "big truck world".....there are giant engine driven fans and they only pull 35-40 HP max maybe.


JIM

domenic tallarita

Bad story,
I had a shop neighbor that did testing as a expert witness. They came over to look at the collection of fan blades I had. They were testing because of a death that happened when a fan blade entered the head of a guy. The guy was hitch hiking and walked up on a stalled car. He asked the car owner if he would give him a ride if he could get the car going. He got the car engine running, then revved the engine to the limits. That's when the blade came off and into his head.

Dom

cv67

DIdnt some cars or truck years ago come with a white plastic fan mounted to a clutch (or not). Capri?

Kid Vette

Wow! Blast from the past! Just an update, I scored a stock 5 blade clutch fan on ebay shortly after starting this thread. No complaints.

C6_Racer_X

Nylon fan blades (naturally a milky translucent white color) on a thermal fan clutch is pretty common since the 1990's. S10s, Blazers, Rangers and Explorers all had them for many years. I would think Mustangs and Capris had them as well (late 2nd gen ones). Not sure, but I think late 3rd gen F bodies had that setup as well.

ZAKsPop

Engine Masters is now on a subscription service. It used to be on YouTube but not anymore.

69427

If that video mentioned earlier is the same one that was posted on the forum a year or two ago, I have to respectfully, but strongly, disagree with the substance/results of that "test". As an engineer, I would get fired if I ran a test like that (I believe the head guy in the video has a journalism degree). To take a bunch of different capacity fans, and do a test that ignores the aero affects of incoming radiator air, ignores the inertial effects of additional mass in a vehicle due to heavier alternators, electric fans, and relays/wiring, and doesn't seem to be interested in how or why a fan consumes horsepower, seems to be a colossal waste of time and fuel. JMO (I agree with several of the points C6_Racer_X mentioned earlier.)

FWIW, I'll stay with my lightweight flex fan (18 oz), lightweight alternator (7#, as it doesn't have to run an electric fan at idle), and the slightly improved vehicle c/g location due to less mass straddling the front axle. My goal is reduced laptimes, not benchracer dyno numbers.