I have a 1987 k5 blazer, a 1979 k10 pickup and want to put on electric fans. My question is would it be beneficial to keep on the fan shrouds? The electric fans are the univesal ones that vary in size, they also would be puller type because i have trans coolers and engine coolers on front. I also would like to know which is better, two small electric fans or one large one?  

A shroud helps, certainly. Pullers are always better than pushers since when you're moving, pushers are useless (unless mounted in front of the radiator...).
The best combination is that which moves the largest amount of air.  

Please remember that no electric fan can match the air moving capacity of a engine driven fan when conditions get extreme. TO even begin to do so they would require far more electrical power than you electrical system can produce. They are a good way to augment cooling at low engine speed but should not be consider primary if you plan to work vehicles engine to full potential.  

I'm going to strongly disagree with this statement. If electric fans are not good for primary cooling, then why are they used on virtually all high performance cars?
My TA came from the factory with an electric fan. When I was done with it, the 300HP LT1 had been morphed into a 700HP supercharged 383CI monster. Guess what I used to cool it?  

YOu need to think before you type. Your 700 HP car you talk about cannot sustain cooling by any means at a high power level as most high performance cars too. A off road vehicle does not have the benefit of ram air at 100 MPH to help cool it and it usually relies on brute force to stay cool. A engine driven fan can consume 5 to 10 HP and more during pick loads and to develop that much air flow capacity with a electric fan you would need to draw between 350 and 700 amps at 12 volts (or about as much as your car starter) and have a motor that weight 20 to 30 pounds and would have a short run cycle too (like a starter as it would have to be a lot bigger and heavier to be able to have a 100% cycle) Electric fan cooled vehicles rely on thermal mass to get them through short peak demands at low speeds and then cool during periods of low thermal demand. Pull any of you electric fan vehicles hard at low speeds in hot weather and they will overheat. See "my" idea of a proper cooling system is one the NEVER gets warm not matter what I do with it and my 4x4's are like that. Even my 89 4x4 burb that I bought new will not break a sweat in 100 degree temps with A/C blasting even at low speeds. Sure the clutch fan gets a bit noisy at times like that but I do not care because it is keeping its cool and mine too. A few years ago I towed a 13.5 K lb trailer some distance in 90 plus degree weather with my 2000 K3500 SRW P/U while we were chilling inside blowing snowflakes and even in traffic with this load it never got anywhere near 210. No electric fan on it, only a massive 10 bladed clutch fan on it. No electric only fan on a big SUV is going to provide that kind of cooling. There is a lot of misconceptions about this out there and you obviously share these misconceptions. Aux cooling fan can boost cooling at a idle sometimes as well as boost A/C performance sometimes so have than a a aux in not bad on a big SUV but as a "only" it is a different matter.  

Thanks Snoman,  you might have saved me from a $700 mistake.

Hi,

 I wanted to see what kind of response this Jeep I built would bring.  I spent 3 years of weekends building it and often used parts and tips from your magazine.  Thanks for the advice.  I had zero experience building a rig and you made it fun and possible.  

I bought a 1997 Dodge 3500 wrecker with 120k miles.  I shortened the frame from 14 ft to about 9 ft.  I had to move the front axle forward 11 inches to fit the wheel wells on the Jeep using rubicon control arms and Ford spring/shock towers (tip from 4 Wheel Parts manager).  I also moved the rear axle back about 11 inches because I didn't like sitting over my rear axle,  if you know what I mean?  I reversed the rear spring shackles for lift eliminating blocks and rolling the yoke in perfect alignment to the 5 speed tranny. NV3500?  The Jeep dash wouldn't fit over the Dodge factory AC components ,  so I cut the face off,  shaped a 2x12 pine board to fit, and screwed it all together.

The only thing Im worried about are the front springs,  I screwed the Ford coil spring into the Dodge coil spring.  They fit tight,  and I even drove it around my field a bounced around a little and they didn't collapse or pop out.  So I tacked them together where they touched with a welder.  I tried not to heat them up too much to weaken them ,  so far so good,  I have put 1000 miles on it so far with no problems.  I can't afford the coilovers that would work better .  $1400 ??? Ouch.  Maybe somebody can make some springs for me?  

The Dodge was 2 wheel drive so I didn't have a transfer case,  and I had to buy the front axle from a junk yard.  Im thinking of trying to make the front axle  electric drive by running a big generator with the torque from the Cummins.  Kinda like a freight train or WWII U-boat.  Diesel / Electric style.  If I can get 55 mph on electric I will take the back roads everywhere,  who needs a highway,  and also I will have 4 wheel drive capability.
I would also like to put an "air ride system" under the body and for the suspension to smooth the ride.  I had to cut 1 inch off the fan blade to make room for the steering pump,  so I need a 5700 cfm electric radiator fan to eliminate the belt driven blade that might be out of balance now that I cut it.  The fans I found are $700 to $800, ouch again !

I bought a hydraulic winch on ebay for $70,  I thought I could just buy a motor for it and I would be golden.  Wrong.  It turned out to be a 3000 lb winch that was the dimension of a 12000 lb winch.  Plus the DP winch motor runs $600 .  Ouch again.  But I have the PTO, pump, and hydro tank to run a 12000 lb winch.  I just need the winch.  Used or new.

Im on a low budget,  as you can tell,  so I would love to find sponsors that see an advertisement in my Jeep and might help me out with some parts.  I guarantee FREE LABOR!  Im rich with time, and I love to drive if its a matter of going to car shows or events.  Im enthusiastic about quality parts and businesses that actually care about their customers like me.  So I can sing praise and pile it on.

5.9L Cummins Turbo Diesel (120k original miles)
factory AC
airbag
cruise
PTO
4.10 gears
dually wheels
dana 60 axles
BFG tires
LED lights (I made the bezels)


Thanks, Joel  

Snoman, i have read many of your posts and you always have good and reliable info. I live in Arizona and am a auto mechanic, i know all about cars getting hot. I do not dissagree with you but both of my vehicles have taller radiators with four cores. The blazer is stock and has a clutch fan that does not work (you can stop it while it is running) and the p/u has a very well built 350 with a flex fan. The reason why i want to put on electric fans is because i do alot muddin and wash crossing that i want to turn off the fans momentarilly while doing so. Because almost every time the mud and water bend or break the fan blades. Also on my 79 p/u i was muddin and the bent fan blade wobbled the water pump bearings came loose and the fan went everywhere. So i just wanted a second opinion to know if keeping on the factory fan shroud would be beneficial?  

Actually, I do think before I type. I also think before I click post.
My TA does fine in all situations. Including idling in city traffic. Further, the 383 stroker in my Wrangler also lives just fine with an electric fan. Doesn't matter if I'm tooling down the interstate or crawling through the rocks of the toughest trails in CO. Likewise, the 408 stroker in my Dodge uses an electric fan. Down the highway, on any trail, towing a trailer, or running the nasties at Attica during RTCC. No problem. Even with the AC running while competing.
However, you seem to be the sort who must have the last word. So tell me again that I don't know what I am talking about, and I'll not reply. You are welcome to the last word. Have a nice life.  

Lets do some simple math here. (simple for me anyway). It takes .24 BTU to heat one pound of air 1 degree at sea level and there is about 13.2 cu ft in a pound of air. A gas engine is at best is about 30% efficient with about 30% going to cooling system and the remaining about 40% going out the tail pipe. Using this also remember that to produce 300 HP you need to "burn" about 1000 HP of energy in fuel to drive engine. Being that there is 746 BTU in a HP that means you have to consume or burn about 746,000 BTU/hr and this times 30% means you have to loose 223,800 BTU/hr through cooling system just from fuel (actual heat to remove will be higher because of heat from friction and shearing of oil) Assuming a 60 temp rise in air passing through core you will need to move approx 3500 CFM at sea level. Now it takes about 1 hp to move about 1500 CFM with a 1 PSI pressure drop or increase across fan (which is reasonable to assume given core) which means that with about 745 watts in a one HP divided by 13.8v equals a current draw of about 54 amps is needed but this does not even factor in efficiency of fan, Furthermore, we take 3500/1500 and get about 2.3 HP is required to provide air flow needed to dissipate heat or about 126 amps) BEFORE fan efficiency losses. Also at say 8000 feet in elevation it takes about 25% more airflow to move same amount of heat because air is less dense. All you can "hope" to do with your 30 or 40 amp fans is cool engine during periods of low heat load and depend on thermal mass (or high forward velocity forcing air through core) to get you through times of high heat load because the fans cannot cut it if you look at the physics involved. You will also generally find that fans are kinda over rated on CFM and the do not take real world pressure drop into factor nor air density which changes a LOT with temperature and altitude which can greatly effect CFM flow and allow them to skew ratings.

(BTW if you want to we can expand this to factor vehicle velocity vs frontal area and is theoretical impact of air flow through core)  

I have to agree with snoman.  I have never seen an electric fan be able to pull close to the amount of air as an engine driven fan.  How many tractors have electric fans?  They are a slow moving vehicle that cannot rely on ram air effect from high speeds and are under load at slow speeds.  However there are situations where an electric fan is the right answer for certain applications.  So if you are smart about it and know that you can get away with using an electric fan I think it is the way to go.  But if you don't want to worry about it and keep your cool all of the time stick with a good clutch fan.