I have been having some 'running hot' at Idle issues under this thread:

http://www.chevelles.com/forums/showthread.php?t=182984

and after getting it better, I have come to the conclusion that I still don't have enough idle airflow. I'm not 100% sure that the new HD clutch is engaging as I would think that my 7-blade fan would be giving off quite a roar...and its not.

I installed the fan (stamped 'front') with front towards the front of the vehicle. But looking at it the blades are curved towards the rad. It would appear that with the blades curves towards the engine it would pull more air. Is this correct?? I've never used a clutch fan bvefore and really want to keep it...but if I can't get this figured out I'll have to go back to a flex fan.

Could I have it in backwards?? Here is a pic of it insalled currently:

Looks backwards to me.

Looks backwards to me.

:yes:

Looks backwards to me.

Me to!:yes:

:o
I looked at your car numerous times this past weekend and never noticed...:sad:

it looks correct-you may have other issuses

it looks correct-you may have other issuses

Which way does the fan rotate? Why would the tips be slanted towards the radiator?

If its backwards you should feel air flowing out the front of the rad, instead of out the rear behind the fan.:D

You'd have to rotate it backwards to get the air to blow in the opposite direction. Installing the blade backwards just reduces the efficiency of the fan.

You'd have to rotate it backwards to get the air to blow in the opposite direction. Installing the blade backwards just reduces the efficiency of the fan.

That is correct.

The fan is installed correctly. While setting in the car looking at the fan the fan will rotate counter clockwise. When the engine is running is the air blowing front to back?

That is correct.

The fan is installed correctly. While setting in the car looking at the fan the fan will rotate counter clockwise. When the engine is running is the air blowing front to back?

The air blows in the same direction no matter which way it's installed. Why are the tips of the fan pointed towards the radiator? Do you want air to flow in that direction? Why is the primary air moving surface interrupted by a plate with rivets in it? If I was designing a fan I would put the support plate on the low pressure side of the blade. I'll bet this fan will be much more efficient after it is turned around.

The fan rotates clockwise when your perspective is standing in front of the car looking at the engine.
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The fan does pull air through the radiator
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The fan is stamped front, the side stamped front is facing the front of the vehicle
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Its a GM fan
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The blades are curved towards the radiator
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It would appear that if it was turned around with the curves facing the engine, it would be more capable of pulling air through the radiator.
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It does not matter which way its mounted, it will always pull the air in the right direction when its turning in the right direction...BUT one way will be more efficient than the other
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I never do hear that 'roar' that you would normally hear with stock 5 & 7 blade clutch fans. I have tried 2 NEW clutches to rule out a bad clutch.Can someone look at their GM fan and compare to mine?

In the time it takes to take a pic, link it, post it and view it you could turn the blade around. After changing 2 clutches you must be pretty good at it.

Will get a pick of mine when I get home this weekend. But, I think mine is more straight at the blade tips.

Can someone look at their GM fan and compare to mine?


I did. Two different vehicles.

In the picture yours is installed correctly. Tip are curved towards the radiator but not as drastic as yours. Possibly you have an incorrect shroud for the fan and the blade tips were aggressively bent for additional fan to shroud clearance. Blades on on the front side of the hub. The blades are also curved to create and airfoil (lift) effect. Turning the fan around will defeat that purpose.

Rob, looked at my 67 ss396 when I got home the blades are rotated just as yours are, however my 7 blade has just a slight curve on the tip of the blade, not the huge curve you have on yours. Jb

I did. Two different vehicles.

In the picture yours is installed correctly. Tip are curved towards the radiator but not as drastic as yours. Possibly you have an incorrect shroud for the fan and the blade tips were aggressively bent for additional fan to shroud clearance. Blades on on the front side of the hub. The blades are also curved to create and airfoil (lift) effect. Turning the fan around will defeat that purpose.

I just looked at several fan/clutch combos on ebay. They were used auctions so they were assembled. They look to be installed just as mine is.

If the tips were bent, it was done very well because they don't appear to be damaged and they do look simmilar to other 772 fan photos I saw on ebay as well.

The shroud is new, repop.

The fan was bought for a TC'er who sells on e-bay description as follows:

original 7 blade GM "3947772 style" fan removed from a 1970 El Camino with the SS 396 engine and a/c. The fan is in excellent condition with no loose or bent fan blades and all of the mounting holes are in excellent shape as well. This style fan was used in all big block, a/c car, and high performance engines where extra cooling was needed for your engine. This appears to have been a dealer replacement part as there is no date coding on it that I can see. The hub is stamped FRONT with a 94 in another part of the hub and the letter H stamped in yet another area. The paint on it is in good condition but could be given another quick coat of paint to make it look perfect for a show car. The diameter of the fan is just short of 18".


I do wonder how it would react if I flipped it around anyway. I'm not getting enough idle airflow with this fan, which I can't understand if its installed right.

Me to!:yes:

Me three :yes:
The blade pitch is correct to pull air and would be the same IF turned around but those blades sure don't have much of a cup to them.

the blades are rotated just as yours are, however my 7 blade has just a slight curve on the tip of the blade, not the huge curve you have on yours. Jb

Tip are curved towards the radiator but not as drastic as yours. The blades are also curved to create and airfoil (lift) effect. Turning the fan around will defeat that purpose.

Just looked at some other 772 fans and yes my 'like a 772 fan' has more curve in the tips. I wonder if this is the problem?

What is airfoil(lift) and how does it affect the fan?

Maybe its time to get another fan.

Me three :yes:
The blade pitch is correct to pull air and would be the same IF turned around but those blades sure don't have much of a cup to them.

Thats what drew me to this in the first place, thats why I thought I might benefit from flipping. It would 'grab' more air?

What is airfoil(lift) and how does it affect the fan?




Think of the blade as an airplane wing. The curve of the blade forms a shape similar to that of an airplane wing. That curve aids in performing lift. In the case of the fan helps in pulling air through the radiator.

http://virtualskies.arc.nasa.gov/aeronautics/tutorial/images/AirPressure.gif

Turning the fan around (inverting the airfoil) will cancel out part of the lift/pulling effect making it less effective.

Ahh, thats clearer now.

Also I found my fan HERE (http://www.camaros.org/coolingsystems.shtml), near the bottom, listed as the unstamped fan. Interestingly enough neither the fan I have or the one in the link has any cupping to the blades. Could be why it flows so poorly. Almost wants to make me try an original fixed 4 blade I have laying around for comparison.

The fan is installed backwards I can assure you. The fan will pull air through the radiator the way it is installed but not very efficiently. If you look closely the fan blades will have a staight edge on one side and a curved edge on the other. the straight edge (leading edge) cuts into the air and the rounded side (trailing edge) will have a slight "cup" to it that pushes the air backwards into the engine compartment. I am 100% sure of this , I am a commercial hvac tech and I find fan blades installed incorrectly all the time on equipment causing them to run hot for years and nobody noticed. A radiator and an air conditioner are basically the same thing -a heat rejection device. a fan is a fan, they all work on the same principle and are designed similarly whether its a car or a 100 ton office building AC fan. If you flip the fan around I promise you will get the airflow the fan was designed for.

Would this be the theory behind the flex fans?

I don't want to step on any bodies toes here but a fan blade and an airplane wing are two entirely different animals. A wing works by air flow passing over and below causing lift. a fan blade works on a different principle - cutting through the air and cupping and pushing the air behind it causing a low pressure in front of the blade . the long staight side of the blade does the cutting the shorter rounded side does the cupping. If you have a fan around the house ( the oscilating type for circulation) look at the way the blade is pitched and which direction it turns and then look under the hood you will see what I mean

The fan is installed backwards I can assure you. The fan will pull air through the radiator the way it is installed but not very efficiently. If you look closely the fan blades will have a staight edge on one side and a curved edge on the other. the straight edge (leading edge) cuts into the air and the rounded side (trailing edge) will have a slight "cup" to it that pushes the air backwards into the engine compartment. I am 100% sure of this , I am a commercial hvac tech and I find fan blades installed incorrectly all the time on equipment causing them to run hot for years and nobody noticed. A radiator and an air conditioner are basically the same thing -a heat rejection device. a fan is a fan, they all work on the same principle and are designed similarly whether its a car or a 100 ton office building AC fan. If you flip the fan around I promise you will get the airflow the fan was designed for.

Six of the GM products I just looked at have the rounded tip on the leading edge. The straight edge is on the following side of the blade. Coincidence that they are all on wrong. :noway:

I don't want to step on any bodies toes here but a fan blade and an airplane wing are two entirely different animals. A wing works by air flow passing over and below causing lift. a fan blade works on a different principle - cutting through the air and cupping and pushing the air behind it causing a low pressure in front of the blade . the long staight side of the blade does the cutting the shorter rounded side does the cupping. If you have a fan around the house ( the oscilating type for circulation) look at the way the blade is pitched and which direction it turns and then look under the hood you will see what I mean

I disagree. An airplane wing and a fan blade are the same. While the airplane makes lift, the fan does as well, which makes the air move. The cupping of the blade is just like wings of days ago. The cup is camber and creates the airfoil, causing the flow.

The leading and trailing edge have nothing to do with what way the air wants to go as in your previous post. They only increase efficiency and reduce noise.

The only 2 things that are making this fan pull air is the pitch(angle of blade) and the camber(cup shape).

I don't want to step on any bodies toes here but a fan blade and an airplane wing are two entirely different animals. A wing works by air flow passing over and below causing lift. a fan blade works on a different principle - cutting through the air and cupping and pushing the air behind it causing a low pressure in front of the blade . the long staight side of the blade does the cutting the shorter rounded side does the cupping. If you have a fan around the house ( the oscilating type for circulation) look at the way the blade is pitched and which direction it turns and then look under the hood you will see what I mean


You just explain the same principle of lift in two different ways.

I don't want to get into a scientific arguement with you guys especially arge about cars, engines, whatever but this is what I do for a living- I work with fans from the tiniest 1/100hp to 50+ hp blowers. the fans is backwards and his car overheats. a fan is a fan. they are all prop fans they work the same way no matter the application ,its all air movement. I f he wants to eliminate the overheating problem then reversing the fan would be a huge leap in the right direction.

If he wants to eliminate the overheating problem then reversing the fan would be a huge leap in the right direction.

While several hours ago I would have agreed with you right away, based on fan design and what even common sense says which way would generate more flow. BUT after looking at all the factory type fan photos I could find online, they are all installed just the same as mine.

The only difference I can see is that my particular fan (unstamped 772 type) differs from most as the curves tips of the blade are more pitched than a 772 fan, and the blades themselves are not cupped as in a 772 fan.

I would actually like to flip it and give it a try, just to dispell any myths about operation, BUT after closer inspection of the photo of my fan I posted above (I'm not near my car right now). It appears that the fan might interfere with the clutch body if I try to mount it flipped. The way its mounted now, the leading edge (closest to clutch body) is angled to clear the clutch...look closely.

Thanks for the input and keep 'em coming. ALSO, how about some suggestions on what to do.

Well, I'll be.... :clonk:
Pic taken minutes ago of the clutch fan on my '66 wagon.
One thing to note...I believe all the fans I've ever seen have each of the individual fan blades riveted to the front side of the fan hub (as shown).

Well, I'll be.... :clonk:
Pic taken minutes ago of the clutch fan on my '66 wagon.
One thing to note...I believe all the fans I've ever seen have each of the individual fan blades riveted to the front side of the fan hub (as shown).


Notice the more rounded corner on the leading edge. Same as the Factory Assembly Manual.

http://i92.photobucket.com/albums/l9/dlplett/Faninstall.jpg

I guess I stand corrected the shop manual doesn't lie

Old car probley just needs a new radiator in it...:D

I guess I stand corrected the shop manual doesn't lie

Problem is: can't even get it mounted the other way because it itnerferes with the clutch body.

Old car probley just needs a new radiator in it...:D

Rad is good, its definately an idle speed airflow problem, check link in first post.

Just can't seem to get a good flow of air with that fan.

your post shows you have a four core, thats good, but is it new? or has it been checked by a raditor shop for proper coolant flow? are all the fins on the rad straight, and the trans cooler It looks like you may have one by the pic, if you do have one did you check fins on rad behind it? why are you running water? What is water wetter? I quess it has corrision preventive stuff in it, I hope... If all that stuff is up to snuff, get a new fan and clutch and try it... u shouldnt need any more than that to keep her cool....

your post shows you have a four core, thats good, but is it new? or has it been checked by a raditor shop for proper coolant flow? are all the fins on the rad straight, and the trans cooler It looks like you may have one by the pic, if you do have one did you checked fins on rad behind it? why are you running water? What is water wetter? I quess it has corrision preventive stuff in it, I hope... If all that stuff is up to snuff, get a new fan and clutch and try it... u shouldnt need any more than that to keep her cool....

Why water?: New engine, its summer, was easier.

Why wetter?: Lube & corrosion protection (for use w/o anti-freeze)

Radiator?: 4 core with BB-A/C size tanks, 7 years old.

Trans Cooler?: Mounted correctly no bent fins behind it.

The entire cooling system worked perfectly with a 'hotter' small block I had in it a few months ago. The only difference now is I removed the A/C (that should help air flow), and I changed from a flex fan to a clutch fan.

First I tried a new non-thermal clutch, then went to a new HD thermal clutch. The thermal made it better but not fixed.

A quick fan clutch check = with the engine at operating temp the fan should stop rotating within 1 1/2 revolutions after you shut-off the engine at idle.

I don't want to step on any bodies toes here but a fan blade and an airplane wing are two entirely different animals. A wing works by air flow passing over and below causing lift. a fan blade works on a different principle - cutting through the air and cupping and pushing the air behind it causing a low pressure in front of the blade . the long staight side of the blade does the cutting the shorter rounded side does the cupping. If you have a fan around the house ( the oscilating type for circulation) look at the way the blade is pitched and which direction it turns and then look under the hood you will see what I mean
I gotta respectfully disagree.

The major issue I have here is that most everybody around teaches the WRONG principle of how a wing generates lift. If it were all about the air moving faster on one side than the other then a symmetrical wing section or even a flat plate wing would not fly. But they do fly and fly very well, so forget about what you were taught in school or told by the FAA. Wings fly by moving air, plain and simple. So they are exactly like fans and propellors with respect to the movement of air.

Now the fans used in Chevelles all utilize a flat plate airfoil of some kind, which is really not the most efficient air mover (as an aside it would be interesting to make a cooling fan with symmetrical airfoil variable pitch blades - it could use virtually no power when not needed and cool like hell when needed). But it can be helped by adding some camber which is the curvature across the blade from side to side. But not too much camber or the "wing" stalls and you get turbulent flow, not good for anything but sucking energy and turning it into noise.

From an aerodynamic perspective the ideal would be to have a vertical plane on the end of the blades as many electric fans do. This prevents air from slipping around the end of the blade from the high pressure side to the low pressure side, which generates circular vortices and more of that energy sucking noise. Lacking a ring around the fan, changing the shape with leading edge curves (or trailing edge curves) and bends in the right direction can accomplish much the same thing.

But I think we can pretty much agree that aerodynamics was not close to the top of the list when the 772 fan was designed. Sure moving air was important. But overriding all that was reducing noise. And I would guess that the backwards (aerodynamically) bend of the tips, like the semi-random blade spacing, were found to reduce fan noise.

With respect to the current problem, if you have found that the fan only mounts one way then it must be on correctly. All the pictures I have seen do have the hub on the back side of the blades as yours is. It also appears that the curve/camber of your blades is correct as mounted. Which does not leave much. Perhaps time to jump up to an aluminum radiator.

Want to interject something here. The radiator appears to have some , minor damage, not a lot but worth noting. Also, guys will often apply too much paint to a radiator, one lite coat is it, mutiple coats insulate the radiator (heat kept in). Last point, when the motor was assembled, were the water passages in the block & heads cleaned out? I have seen passages (especially in heads) that were nothing more than pin-holes originally from the factory. Also, big blocks have changed to parrallel cooling as opposed to series cooling, controlled by the head gasket used. Two other areas of note are the water pump internal clearances and the intake water port/head water port alignment.

Want to interject something here. The radiator appears to have some , minor damage, not a lot but worth noting. Also, guys will often apply too much paint to a radiator, one lite coat is it, mutiple coats insulate the radiator (heat kept in). Last point, when the motor was assembled, were the water passages in the block & heads cleaned out? I have seen passages (especially in heads) that were nothing more than pin-holes originally from the factory. Also, big blocks have changed to parrallel cooling as opposed to series cooling, controlled by the head gasket used. Two other areas of note are the water pump internal clearances and the intake water port/head water port alignment.

Yes the Rad is not perfect, but did its job behind a 'hotter' engine. It is 7 yrs old and was repaired once but is clean and flows well.

As a far as the other issues they have all been gone over and it is dertermined to be an idle airflow issue. These unstamped 772 type fans have almost no 'cupping' on the blades and I really don't see or hear the roar of airflow that I should have with the 7 blade clutch fan.

In my previous engine I had a tremendous amount of idle flow with the flex fan and it could idle all day at 185. The flex fans tend to scare me, and I hate getting cut by them when installing ir doing other work...damn they are sharp.

I have been having some 'running hot' at Idle issues under this thread:

http://www.chevelles.com/forums/showthread.php?t=182984

and after getting it better, I have come to the conclusion that I still don't have enough idle airflow. I'm not 100% sure that the new HD clutch is engaging as I would think that my 7-blade fan would be giving off quite a roar...and its not.

I installed the fan (stamped 'front') with front towards the front of the vehicle. But looking at it the blades are curved towards the rad. It would appear that with the blades curves towards the engine it would pull more air. Is this correct?? I've never used a clutch fan bvefore and really want to keep it...but if I can't get this figured out I'll have to go back to a flex fan.



Could I have it in backwards?? Here is a pic of it insalled currently:

Wow 40 reply to the post 370 views .
Theres something that bothers me about these clutch set ups ...they list hd
and a/c Ratings .. but nobody seems to know what temp spring they have in them .. is it locked up 90% at what temp ...210 degrees ... 195 degrees
185 degrees ... if it seems its not pulling air at idle .. the termal spring or lock up may not be kicked in yet while your checking it .
There obviosly working off hot air comming trough the rad and a/c condencer
And we have heard the 80 caprice cop car unit is a good one anlong with a few vette models ...but dog gon it can anybody give a thermal rating ??????

anybody ??
Don

Wow 40 reply to the post 370 views .
Theres something that bothers me about these clutch set ups ...they list hd
and a/c Ratings .. but nobody seems to know what temp spring they have in them .. is it locked up 90% at what temp ...210 degrees ... 195 degrees
185 degrees ... if it seems its not pulling air at idle .. the termal spring or lock up may not be kicked in yet while your checking it .
There obviosly working off hot air comming trough the rad and a/c condencer
And we have heard the 80 caprice cop car unit is a good one anlong with a few vette models ...but dog gon it can anybody give a thermal rating ??????

anybody ??
Don

http://www.haydenauto.com/installation/faqs.htm

I love search engines...I'll bet that if you would send a nice letter to them on your company letterhead and let them know that you're in the business and would like more information about their clutch fans, so you could recommend their products, they'd fix you right up. My $0.02

http://www.haydenauto.com/installation/faqs.htm

I love search engines...I'll bet that if you would send a nice letter to them on your company letterhead and let them know that you're in the business and would like more information about their clutch fans, so you could recommend their products, they'd fix you right up. My $0.02

good info .. some things of interest there

Standard Duty Thermal
Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch. (1-1/2" of pitch) Flat plate impeller design with 30 Sq. In. of working surface.

Heavy-Duty Thermal
Turns the fan 80-90% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans. (2 1/2" of pitch). Land and groove design with 47 Sq. In. of working area allows higher operating RPM's.

Severe Duty Thermal
Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2- 1/2" of pitch). Land and groove design with 65 Sq. In. of working area. Larger working surface provides cooler running and longer life expectancy.

Q. My fan clutch makes a loud noise when started cold. Is that normal?
A. Yes, most fan clutches allow the fluid to drain into the working area when shut down. At startup it may take 1-2 minutes for the clutch to slow down.

Q. I have a late model Chevrolet or GMC truck. The original equipment fan clutch does not engage until the (engine is past 210° F.) Does Hayden make a fan clutch that will keep the engine cooler?
A. Yes, our fan clutches for these vehicles are specifically designed to engage at lower temperatures than the original equipment fan clutches that they replace.

When I get home, I can get the number of my clutch, it works very well at idle. From the sound it (fan) makes, I would bet it is the severe duty version. Probably eats HP, but it does a great job cooling.

OK, this thread got my curiosity up and I went out to look at a stock GM clutch fan still on the pump. Looks a lot like yours. Have you let the engine idle and watched for the cycling of the clutch fan? It is pretty easy to see (and hear) when the clutch engages. Having tried two clutches is good, but maybe you got two that were not all that healthy ( did this with new fuel pumps one weekend). Let it idle and watch for the cycling.

OK, this thread got my curiosity up Have you let the engine idle and watched for the cycling of the clutch fan? It is pretty easy to see (and hear) when the clutch engages. Having tried two clutches is good, but maybe you got two that were not all that healthy ( did this with new fuel pumps one weekend). Let it idle and watch for the cycling.

Yes Iv'e tried, but once it engages it never stops because the temp keeps climbing. I've also check the coolant temp coming into the radiator and its within 5 degrees of the guage from about 170 to 225 (when I shut it down). Temps in the shroud are about 160 at (180 coolant) and 180-190 when coolant is 200 and over

I did noticed my fresh radiator full of water and wetter was very dirty (after only breakin-in plus 1500 miles), so I flushed several times with water and then refilled with water and put a jar of 'flush' in.