Mechanical Fans - would like some feedback from the group

[wikd69]

Hey all, help me out here with some questions on fans...

I'm still running a mechanical water pump and fan and I'm trying to increase my air flow at low speeds - my radiator is a heavy Fluidyne unit and does a good job once I get enough air flow through it. It just doesn't get enough air at low speeds or sitting in traffic though once I start moving and get some speed up it does ok. So, I'm swapping out my current mechanical fan for something bigger - I need to find out what other folks are using and get some opinions. Note that I may end up doing an electric pump and fan somewhere down the road, but I'm not there quite yet.

I currently have a 6 blade flex fan, 16.5" diameter and 2" wide, similar to the image below.



I want to step up to an 18.25" fan but have some challenges with space limitations, between the front of the blower drive and radiator. The fan can't be much wider than 2".

I tried a 6 blade Flex-A-Lite 1318, 18.25" in diameter but the fan is 2.25" (too thick). Again, I need to stay within 2" or so wide.

I located the fan below, another 6 blade Flex-A-Lite (1718). It's not a flex fan but is the right diameter (18.25") and width (1.75"). According to the documentation this fan moves a lot of air.



Unfortunately Flex-A-Lite doesn't publish CFM numbers on any of their fans. Is anyone using a fixed blade fan like this ? Will it move air like they advertise? I know the advantage of running a flex blade fan but I'm not all that concerned about horsepower loss. I'm more interested in moving air. Any input or freedback would be most welcome.

[Bob West]

I had good luck using the oem 7 blade fan with a viscous clutch, after I wrecked the car i switched to dual electric flex a lites.

[John_Heard]

X2 w/bob - Go to the junk yard and find a mid 80's big block chevy truck, grab the fan and fan clutch off of it. It'll sound like a helicopter when the flan is engaged but will kick off once the temp drops down. Beast will move a ton of air.

[wikd69]

X2 w/bob - Go to the junk yard and find a mid 80's big block chevy truck, grab the fan and fan clutch off of it. It'll sound like a helicopter when the flan is engaged but will kick off once the temp drops down. Beast will move a ton of air.

You're talking about using an OEM mechanical fan with a fan clutch ? I don't understand what you mean by 'but will kick off once the temp drops down'... Is the fan clutch somehow controlled via a temp sensor or something ?

[John_Heard]

Yes, stock chevy fan with the stock clutch. The clutch kicks it on and off based on temperature. No external sensor needed. For example

"HAYDEN THERMAL FAN CLUTCH -- Standard Rotation, Varies The Fan Speed With Temperature Of The Air Behind The Radiator, Engaged High Speed Operation Provides Maximum Cooling, Disengaged Low Speed Operation Provides Fuel Savings And Noise Reduction, Offers Greater Life Expectancy Than A Non-Thermal Clutch, Briefly Engaged At Cold Start-Up, Engages At About 170 Degrees Radiator Air Temperature About 30 Degrees Lower Than Coolant Temperature, With Hayden's 5-Year Or 50,000 Miles Limited Warranty"

[wikd69]

Yes, stock chevy fan with the stock clutch. The clutch kicks it on and off based on temperature. No external sensor needed. For example

"HAYDEN THERMAL FAN CLUTCH -- Standard Rotation, Varies The Fan Speed With Temperature Of The Air Behind The Radiator, Engaged High Speed Operation Provides Maximum Cooling, Disengaged Low Speed Operation Provides Fuel Savings And Noise Reduction, Offers Greater Life Expectancy Than A Non-Thermal Clutch, Briefly Engaged At Cold Start-Up, Engages At About 170 Degrees Radiator Air Temperature About 30 Degrees Lower Than Coolant Temperature, With Hayden's 5-Year Or 50,000 Miles Limited Warranty"

Thats pretty cool John, I'll check those out.

[wikd69]

Ok, so here's an update.

I ordered/received/installed the new Flex-A-Lite 6-blade fixed fan, PartNo 1718. It seems to fit well and is further away from the radiator than the old smaller flex fan was. The old fan was about 3/8" from the core, this new fan sits about 1" from the core, more better :)

The blades are about half-way inside the shroud, so I've done everything I read about as a best practice. The only thing I didn't do was decrease the size of the water pump pulley to spin things faster. I'm sorta holding that in reserve.

Took the hotrod out for about an hour tonite and it seems to do fine. Of course, it wasn't warm out. I'll try mid-afternoon tomorrow, it's supposed to hit about 95 degrees. That should tell me something about how well this new fan is working.

And...

I bought a new electric fan to put in front of the radiator. It's a 16" Flex-A-Lite, PartNo 116, advertised to move about 2,100 CFM. I figured it'd be a good helper at low speeds, idling around town and sitting at stoplights, etc.

I mounted the fan, used light vinyl tubing to get a good seal of the fan to the core, and turned it on.

HAH !!! That son-of-a-b*tch wasn't able to push any air through that thick Fluidyne radiator. I could feel a little air exiting the back of the radiator, but it wouldn't have been enough to blow out a candle. So the aux fan came back out. Sheesh...

Granted, it was working as a pusher fan and they're not nearly as efficient as a puller, but still !!!!

I'll let ya know how this new fan works in the heat, stay tuned.

Oh, and John ? I didn't think I'd have enough room to use a thermal fan clutch, so it's mounted direct. Seems to work fine.

[John_Heard]

Better look at the RPM rating for the fan using it direct. I'm not sure how fast you can spin those?

[wikd69]

Better look at the RPM rating for the fan using it direct. I'm not sure how fast you can spin those?

Thats a good thought, John.

I did look at the OEM style fans and most of them were rated for only 4,000 RPM. The Flex-A-Lite race fan I ended up using is rated at 7,000 RPM and is designed to be used without a clutch. Steel star with aluminum blades. One of the advantages of using a direct fan is you spin at a derivative of engine speed. When using a clutch, you never spin that high, even when temps are up and the clutch is fully applied. I gather there's some slippage built into the clutch assembly and you don't spin much past 70% or 80% of engine speed. Of course, your mileage may vary. This is based on my reading and research.

I'm using the 18" fan. Here's the max rpm specs for the different size race fans:

15" to 17" - 8,000 RPM
18" - 7,000 RPM
19" - 6,000 RPM

For some reason, the reverse style fans are rated for a higher RPM. Go figger.

Here's a link if you're interested.

http://www.flex-a-lite.com/auto/html/race-fans.html

And you thought race-fans just sat in the bleachers eating hotdogs and drinking beer

I'll take the ride out today in the heat and put around a bit. I'll let you know how it works in traffic.

[John_Heard]

Here's the deal, that fan you have will flex the aluminum blades and pull less air as RPM increases. The OEM steel ones pull a LOT more air and will kick out with the clutch when things cool down plus I think they slip with RPM. Years ago we learned the stock OEM fans pulled more air than anything we could find which was important on a dirt track car that had the radiator half filled with mud. We even ran them direct with no clutch at times and yeah, I think a few might have came apart at high rpm oops...

My old dually had one of those big 7 blade fans on it with a thermo clutch on it. You could hear the fan kick in, sounded like a hell and you could hear it in the cab. The temp gauge would drop right down and it would kick off. Temp climbed and it would kick in. Kind of amusing when you're driving a long distance hearing it work. Anyway, if that fan don't get it done, that's the one to use.

[wikd69]

Here's the deal, that fan you have will flex the aluminum blades and pull less air as RPM increases. The OEM steel ones pull a LOT more air and will kick out with the clutch when things cool down plus I think they slip with RPM. Years ago we learned the stock OEM fans pulled more air than anything we could find which was important on a dirt track car that had the radiator half filled with mud. We even ran them direct with no clutch at times and yeah, I think a few might have came apart at high rpm oops...

My old dually had one of those big 7 blade fans on it with a thermo clutch on it. You could hear the fan kick in, sounded like a hell and you could hear it in the cab. The temp gauge would drop right down and it would kick off. Temp climbed and it would kick in. Kind of amusing when you're driving a long distance hearing it work. Anyway, if that fan don't get it done, that's the one to use.

Higher rpm is not so much a concern - the issue is on the bottom end, pulling more air at low speeds and low-to-moderate RPMs. When I'm actually rolling, say 40 mph and up, I get ram air which pretty much meets the need for heat exchange through the radiator. It's that area below 40 mph that gives me problems. If the fan will move enough air in the 1,000 to 3,500 RPM range, it'll work perfectly for what I need. Anything over that (speed or RPM-wise) is a different issue. And, I don't have the physical room to use a fan clutch - this is my design compromise (recall that this is a blower car with a 3.5", 3-row radiator - see pix below). I needed high volume at low RPM and something that would not hand-grenade at peak RPMs. I prolly won't run this 427 past 7,000 RPM very much.

If this aluminum blade fan does not work, I can still opt for the steel bladed variant in this model - same size, same RPM rating, just with steel blades, and it's still only about $28 for the fan itself, not a big expense if needed. If that does'nt meet the need, the only other option I have would to down-size the water pump pulley to increase the fan & pump speed. I'm holding that option in reserve.

Here's a shot of the installed fan - I have about 3/8" clearance between the fan and blower drive hub and about 7/8" between the fan and radiator core. The fan is a low profile design (1/34" wide) and just fits.