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Anyone know how many cfm the fan pulls?

G

great white

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My 98 has the late, factory 9 bladed clutch fan. Bolted on, not with the big center mounted shaft.

Anyone know the CFM rating for it?

IE: 3000 CFM, 4000 CFM etc.

I'm considering an electric fan. Yup, I've read all the threads and seen the arguments against so let's not do that again here please. I need to know so I can get the feet per minute at least close if not higher if I go this way.

And maybe a Higher amp alternator.........and maybe a bigger.......:mad2:
 
One challenge on figuring out a solid comparison is you'd have to rate/estimate each fan system on/in the specific vehicle so the flow restrictions of the cooling stack/shrouding, etc., were accounted for.

I believe the electric fan ratings come from measurements w/ no restriction before/after the fans - just a boundary separating the fan's intake & output. If that is how they come up w/ the cfm ratings, it's tricky to know for certain how it will perform in the actual vehicle.

The real fuel economy benefits from electric fans comes not because they're inherently more efficient (when running), but because when a fan isn't needed at all, they're not running.
 
Measured a Trailblazer SS 21" 10 blade fan in place with the hood closed. Used MPH of air speed over the stack and averaged it out. Depending on RPM it was under CFM of electric fans (idle) and then went slightly over 10,000 CFM. Ear protection is recommended at higher test RPM's. Yet, people with electric fan conversions have trouble with idle temps and poor AC performance on the above referenced hot rod.

Yet, as said above CFM of electric fans are "No restriction" ratings. No Radiator, hood, engine, or grille in the way.

The Pitch of the 21" 2001 Duramax fan blade is steeper than the above tested fan with 1 less blade. The 2008 Duramax fan is 25" in diameter. This means it will move more air at lower RPM. (Like pitch and the like on a boat prop.)

As far as electrics on a diesel the Hayden guide says the airflow requirements exceed what can be provided by an electric fan(s). (A clutch fan is hardly able to deliver enough airflow for us.)

A pusher fan can help with AC, but, becomes a restriction at higher engine RPM - when the belt drive clutch fan is sucking birds, prius cars, and other small derbis off the road in front of you.
 
great white said:
Whoa!

That's pretty high............:eek:

Most electrics seem to max out at around 4000 cfm or less.

may need to rethink the plan.....I just hate "fan roar" is the problem....
Click to expand...

I have the model 280 electric fans on the Tahoe. They are OK, and no, they don't roar. BUT, I would gladly trade the fans for MORE roar if I could move 10,000 CFM. I believe that these fans (without a stack in front of them) have a max of 5000 CFM.

I only put them on because the body lift interfered with the stock fan running properly. They did help, but I would swap them out for a mechanical if I could. Less to break, more cooling.

-Rob :)
 
One thing to mention, the electrics are gonna be rated lower, but
may actually be close in cooling capacity, the fan / shroud clearance
is much closer on the electric - on the engine driven fan, they had to
allow for engine movement, so clearance is sloppy comparatively.
But the engine driven one has enough capacity to make up for it.
 
BJ over on the old site years ago with one of my mentors in attendance (GMCTD), we had discussion of electric over factory fan, cfm was in 10K neighborhood, in my own vehicles I had the bolt on 9 blade steel, and upgraded to the composite bladed one and cooling is improved.

In pure cfm rating electrics can't match the cfm of the 185+ Hp driven one, I talked to several mfrs of electric and none would recommend theirs vs. the OEM one in a Diesel, it's been a while so possibly something better out there now I don't know.

Also another consideration is what are you planning to do with the vehicle, daily driver you should be okay several guys running electrics, towing heavy or light ??? maybe not the best choice, I tow big very big at times so for my circumstance the Hp lost when fan clutch kicks in is offset by a better cooling flow.

If going electric fans a better alternator is recommended as the factory alt IMO, is challenged to support the basic electrical load the general put on the vehicle.
 
Thanks for the input Tim.

I believe I read the old thread on the place when google-ing around for info.

My truck is 99.99999999% of the time a daily driver, so I'm looking at electrics for increasing fuel MPG, reduced noise and maybe the tiniest bit more "spunk" out of the old girl. My truck barely gets to full temp most days on my regular drive.

Now, upgrading the alternator along with fan purchase (already have one and the wiring relays etc but need a second) may negate any potential savings for quite a few years, which defeats part of the purpose of electrics. I'll eventually be making a 7,000 km drive (west coast to east coast) which may give me enough savings to at least pay for the fan, but the alt would be a loooong time paying off....

That leaves me with reduced noise and a touch of extra pep for the truck.

Still thinking about it.....:)
 
Here's a question:

Can the Duramax fan be mounted to the stock 9 bladed clutch fan in my 98?

I see lots of Duramax "conversion" fan kits around, but they're all around 200 bucks. The Duramax fan is about 50 bucks on rockauto.....

There would be some benefits in reduced weight in addition to cooling benefits, but I'm not so sure about trading off a steel fan for a plastic one.

Most composite/plastic fans I've seen are pretty prone to cracking in a short amount of time.....
 
GW

Is your fan bolted to the clutch with 4 bolts (the earlier models were 6 bolts and won't interchange)? If so the DMax fan will be a bolt on mod. After doing some reading up on this I recently did this on my 94. I did have to trim my upper shroud a bit to fit the larger diametyer DMax fan. There is a rib that goes all the way around the inner part of the shroud where the fan sets. This is what I trimmed out. I didn't have to touch the bottom half of the shroud.

I don't have many miles on this since doing the mod so I don't know how it will do with towing yet. We have a family reunion we're going to this next weekend so I'll be able to report back on how it does next week. So far I've changed the fan and since I needed to replace the thermo crossover (broken) I found a dual thermo crossover to put on there. The PO to this truck replaced the waterpump about a year ago with a stock 94 pump so I'm not changing that to the HO unit unless I have problems.

I got the plastic fan from Rockauto, good price. I remember correctly what I ordered was for a 2002 year.

edit: need to add that I also changed the fan clutch to a severe duty unit.

Don
 
Last edited:
great white said:
Here's a question:

Can the Duramax fan be mounted to the stock 9 bladed clutch fan in my 98?

Most composite/plastic fans I've seen are pretty prone to cracking in a short amount of time.....
Click to expand...

Yes I'm running that config on my 98 truck, and the spin on style on my 98 Burb I had a Hayden SD fan clutch from Kennedy on truck for a while, it kicked in sooner but never disengaged once engaged, I got last 4 bolt Heath used to sell (at a killer price) on my truck now it comes in sooner than OEM, but kicks out earlier than the Hayden SD,

IIRC Heath sells only spin on config now with new pumps, that is what I have on my burb.
 
great white said:
4 bolts.

But, I'm still skeptical about giving up the steel fan for the plastic one from a durability stand point...
Click to expand...

Smack an Elk. the 20" steel fan with it's inertia becomes a lawn mower blade. The plastic fan would stop without as much damage.
 
great white said:
4 bolts.

But, I'm still skeptical about giving up the steel fan for the plastic one from a durability stand point...
Click to expand...

When I ordered my plastic fan there was a steel 9 blade fan also listed. I went for the plastic because of the same reasoning as War Wagon's. I understand your concerns about plastic as I tend to feel the same. However, I've seen pics of where a single blade let loose and created mayhem. They're lethal!!!

Don
 
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