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Discussion Starter #1
One topic I have covered here before is how absolutely pathetic the design of the stock stamped steel fan is. What I have discovered about the stock fan is that it forces most of the air it moves outward, like a centrifugal blower, as opposed to actually pushing the air back toward the engine. The clumsy paddle-blades are raked back from the direction of rotation for some odd reason, which seems to contribute to this problem.

Result? On hot summer days, with the AC on, high-side pressures of the AC system climb to ridiculous levels (300+psi), and engine temps creep up as well. This eventually takes its toll on the R4 compressor, causing seepage out of the front seals. Replacing my fan clutch with a new GM clutch, and even a severe duty clutch made no difference.

So why am I discussing doing anything with a mechanical fan arrangement, rather than just going with an electric fan system? Well, I and GM both agree that for hauling heavy loads, a mechanical fan can't be beat for cooling power. Also, I just had an itch to see if something could be done to improve cooling without tearing the whole thing out.

The solution can be found in the GM truck line, where both V* engine and cooling continued to evolve. Most 1997+ GM trucks came with a nice 11-blade composite cooling fan that is a good sight better than what the 91-93 cars came with. Although they use a spin-on fan clutch, the bolt pattern for the fans themselves stayed the same. This is because GM was slowly phasing out the old metal paddle-blades and going over to what you see below.

Comparison between the original fan (top), and the 97+ truck fan (bottom):



The difference in performance between the two is very noticable. The new fan clearly moves more air, and in the right direction. AC pressures do not skyrocket. Engine temp is solid as a rock.

Only 2 drawbacks:

1. This new fan is slightly larger in diameter. There is more than enough space for it in the fan shroud unless your engine is sagging due to bad motor mounts. It's not rocket science to tell. If your fan looks disproportionately low to the edges of the shroud opening, you need to replace those mounts. Eventually, even your stock fan will begin hitting the lower shroud.

2. You can hear the difference in air being moved. It's not ridiculously louder than the stock fan, but when that fan clutch is locked the tightest, you'll hear it roar. Just listen to any 97+ full size GM SUV and you'll hear it in action.

Other advantages compared to e-fans? I got this fan from the local upullit for $7. I didn't add any electrical load to the system. I didn't have to radically change anything. Whole thing was done in less than 10 minutes.

It goes without saying that you should make sure your fan clutch is in good working order as well, and replace if necessary.
 

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I don't sport the Mechanical fan and have electric but this is Great info. Thanks for taking the time and sharing.


I wonder if aftermarket company like Flex-a-lite offers a replacement fan as well that would bolt on and perform better? Remember getting one from them for my old Camaro years ago.
 

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Discussion Starter #3
Only option FAL has for us is an 11-blade steel paddle-blade fan.

It's either a direct copy, or literally the same steel 11-blade you will find in most 97+ GM full-size vans. No idea why the vans tend to get the steel 11-blade over the composite.
 

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One option a dual electric fan set up has is the PCM can be programmed to turn them on at "x" temp. Many of us have aftermarket tuning for several reasons but for a cooling only intent the PCM could be adjusted to turn on electrics at lower temps

IDK if this electric set up out cools what a "better" mechanical fan blade one would but my point is more along the lines of electric fans can be made to turn on/off at specific temps or even be wired direct with a operator controlled switch

I see many "hot rod/muscle cars" with mechanical fans and also a electric fan on front of radiator...another option for mechanical blade guys.
 

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Good for old trucks too

Thanks for the write up.

The 11-blade composite cooling fan is probably better and lighter than many old fan blades. If the fan bolt holes are the standard ones it will work with "the big three" Of course you have to have the same rotation as the replacement.

Viceroy do you have any tips for getting the fan clutch nut loose? Some do not want to come off. Air chisel and heat is not a option at P&P
 

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On my other cars/trucks the fan blade is the one large nut that threads on WP. I bought a "fan clutch tool" at Harbor freight. Works on my Ford truck and Chevy Astro even though it says for Ford on the tool package

it basically is a big ass fork that slides around the 4 bolts on fan and another big open end wrench for the large fan blade nut. Both are about 1/8" thick so they slide in the tight space

also some auto part stores likely have them in their "loan-a-tool" program
 

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Nice work Viceroy. GM didn't spec the mechanical fan as the heavy duty option for nothing. I have had both electric and mechanical fan B-bodies and the mechanical fan setups moved more air, kept the engine temps more consistent, and were more reliable than the electric fan cars. If I ever buy another B-body, if it has a mechanical fan package, it will KEEP the mechanical fan package.
 

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Discussion Starter #9
Electric fans are great. No denying that. The PCM adjustability with them is also quite nice.

My doing this is more for the people who have a mechanical fan and don't want to go through the trouble of converting to electric, or those who have tow-package vehicles and don't want to take a hit on resale by having electric fans. Roadmaster buyers are especially particular about this issue.

Good to know that the big three share a common fan pattern. This will expand my range of experimentation.

I just discovered that this composite fan commonly found in 97+ Blazers also fits. The blades on it look larger and more aggressive than the ones of the first composite fan, seeming to favor airflow over quietness.



This one roars pretty good with an effective fan clutch, but I honestly can't tell either one is running on full steam with the windows up and ac on.

Pretty sure that's why they used this one on the Blazers, since they have smaller radiators and NVH was less of a concern.

For removing the fan clutch nuts, I use a Lisle tool that clamps around the pulley nuts, and has wrenches with a slot to attach a pneumatic chisel to impact the wrench. Have another tool with pins that slot into the holes of pullies with no nuts on them.

Honestly, I'm going to recommend against junkyard fans. In searching for the right ones, I have come across some that were not perfectly round, and a fan out of round will destroy a water pump in short order. You can get brand new Dorman versions of most of these fans at an auto parts store for $40-50 without ever having to disassemble a junk car.

Looking around, I think the 11 blade above might be the real e-ticket. Most aggressive looking and performing one I've seen.

I'm talking to a friend of mine who works for a race shop about getting these all flow tested. They have a rig to do that sort of thing. Just mount up a fan blade, and it sucks on a shrouded flow meter to measure cfm.

All I know is that my AC pressures refuse to pass 170 psi even in hottest heat, and I cannot get the engine to creep up in temp even when deliberately attempting to heat soak her. Condenser Temps at extended hot idle in drive with brakes applied is 20-30 degrees less than before, where is where things really used to get out of control.

The R4 compressor is really happy. There is no more wetness on front from where the excess pressure used to force a bypass out of the snout.

I'll keep you guys posted on my continued experiments.
 

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Thanks for the write up.

The 11-blade composite cooling fan is probably better and lighter than many old fan blades. If the fan bolt holes are the standard ones it will work with "the big three" Of course you have to have the same rotation as the replacement.

Viceroy do you have any tips for getting the fan clutch nut loose? Some do not want to come off. Air chisel and heat is not a option at P&P
I use a huge crescent wrench and a long handle ratcheting box end...Crescent on the "nut" and the box end on a fan nut, using the next nut as a pivot. If you get them close, you can squeeze the wrenches together with one or both hands. I have popped a few of them that way, and it is pretty easy. It is a tight space though.
 
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