Electric vs Mechanical fan cfm

thermorex · **Posted:** Thu Mar 07, 2013 4:23 pm

Hey guys,

I was wondering if anybody knows the cfm (cubic feet/minute) the mechanical metal stock fan pulls, lets say when fully engaged at 2000-ish rpm.

I was thinking to build an aluminum shroud for the crd on which to mount 4x10 inch procomp fans, activated by a variable speed controller (something like http://m.summitracing.com/parts/flx-31163/media). The reason I would go with 4x10 inch fans is that from the research I made, that is the best cfm that can be squeezed over the crd radiator. The biggest single fan that I've found is a 16 inch and the best of them is way under the cfm of 4x10 inch fans. .

I know for a fact that the amount of pulled air for slow speeds/rpm would be improved by 4x10 inch fans but unsure what the need is for greater rpms.

I have something similar on my xj and works great even in the hot summer (tested in Alabama last year), I'm just not sure what the values for a proper cooling should be for the crd.

Thanks a bunch!

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

The stock mechanical fan (at full engagement) will pull about 5400 cfm at rated speed (4000 rpm engine). You will be hard pressed to find another fan that will pull more air within the space limitations.

thermorex · **Posted:** Thu Mar 07, 2013 5:21 pm

GreenDieselEngineering wrote:

The stock mechanical fan (at full engagement) will pull about 5400 cfm at rated speed (4000 rpm engine). You will be hard pressed to find another fan that will pull more air within the space limitations.

Thanks Keith. The cfm rating I personally measured for a 10 inch procomp fan was around 2,500. I used a cheap anemometer from eBay to get the air speed in inch per minute, then I measured the pulling area of fan like this: I calculated the area of the 10 inch fan, then subtracted the area of the motor (which has a 4.5 diameter and needs not to be considered since air doesn't move through) then multiplied the resulting area with the air speed to get the cfm. This measurement is for a fan that doesn't have any restrictions such as radiator, condenser, etc, which is definitely an ideal, maximum cfm that will never be achieved. So 4 fans would yield to 10,000 theoretical maximum cfm. What I don't know is how this numbers would change when everything is mounted on a shroud.

On the other side, the procomp fan has 900cfm on their specs... Don't know how they got that number unless what I've done is totally wrong... Also, on my xj I have a 3 fan shroud, using the same 10 inch procomp. I have purchased the whole kit from DB offroad:

http://www.dirtboundoffroad.com/featured/xj-–-electric-fan-conversion-kit/

And I also have no clue how they calculated their cfm, the minimum for 3 fans seems to be little over 4000 cfm. Stock xj can pull max 3200 or 3600 or something similar.

Based on my measurements and DB offroad, I'd say a 4 fan should have a minimum 5300 cfm, but, that depends greatly on what obstructions are in front of the fans.

As a side note, I've tried an electric 16 inch fan, rated at about 2500 cfm, with a partially open thermostat (didn't know at that time) and while testing that, the engine heated to the point of running constantly the electric pusher, which hasn't happened with the stock fan.

If anybody else has some ideas/experience with an e-fan conversion for crd, I'd appreciate the input. I'll probably go ahead and try the 4 fan conversion anyways, as soon as I get my shroud plans and the end product

Glend · **Posted:** Thu Mar 07, 2013 6:04 pm

Keith do you know what the V6 fan pulls? I am running the Hayden 2509 clutch and the V6 fan, temped to put the stock CRD fan back on cause I hear rumours its better with the Hayden clutch.

Sent from my EBM727KC using Tapatalk 2

papaindigo · **Posted:** Thu Mar 07, 2013 6:13 pm

I almost hate to ask but why bother? The stock metal fan or 11 blade nylon fan combined with the ca. $50 Hayden severe duty fan clutch engages well before any over heat curve starts. I note you have an 05 and the OEM 05 fan clutch is a known weak point so a Hayden is a good upgrade. Assuming the proper coolant; radiator/intercooler/AC condensor are not clogged; and a function thermostat the CRD has ample cooling and if any of those things are in failure mode, so to speak, electric fans won't fix the real problem. About the only thing, other than the Hayden, I'd consider is an auxillary transmission cooler just behind the grill (there are several install strings on the forum) which does add extra cooling for the tranny and takes a bit of a load off the AC condensor which houses the OEM tranny cooler in the bottom.

FYI my son, stoutdog, ran his 06 in Tempe, AZ (temps well into the 100sF) for 3 years with zero overheat problems and we hauled out of that valley on a 105F day with a fully loaded CRD pulling ca. 2,000 lbs of trailer and the temp gauge never twitched above the normal slightly left of vertical.

thermorex · **Posted:** Thu Mar 07, 2013 7:00 pm

Honestly, I just don't like mechanical fans period... Lol. It's not the decreased mileage, it's more from performance point of view. In theory, the proper e-fan can cool better (especially at low rpms) and when combined with a variable speed controller it's just perfect. Never had a cooling issue (aside of bad thermostat) with the stock fan on crd, even though I still have the stock clutch. I also don't tow as most hardcore towers in this forum either, I maybe tow once or twice a year and that's only my one axle trailer from Home Depot to home. Maybe 1500-2000 lbs tops, all combined, for 4-5 miles.

It's not comparing apples to apples when I refer to my xj, stock cooling for that car just plain sucks, but I've noticed a huge difference in cooling using e-fans. Also, you can disengage the efan when crossing water.

Regarding tranny cooler, I already have in my garage this cooler:
http://item.mobileweb.ebay.com/viewitem ... 0893132781

waiting for me to install with 2 7 inch efans. The only problem is to find a propper space under the bumper, lol. On the xj, same cooler never heated the tranny more than 170 degrees, summer and low offroad speed, and I also have a thermal bypass due to cold weather.

Bottom line, I agree, this is probably not a necessary mod, but since I have most of the parts already, I plan to do it.

user113 · **Posted:** Tue Oct 08, 2013 10:18 am

The cool thing about electric fans is you can put in a switch to turn them off completely for water crossings (if you do water crossings...).

Brianawd · **Joined:** Wed Apr 03, 2013 12:59 pm **Posts:** 130

http://www.ebay.com/itm/JEEP-LIBERTY-CR ... 03&vxp=mtr

Some one already put a fan kit together for the CRD.

mass-hole · **Posted:** Tue Oct 08, 2013 11:51 am

Brianawd wrote:

http://www.ebay.com/itm/JEEP-LIBERTY-CRD-DIESEL-FF-DYNAMICS-EXTREME-ELECTRIC-COOLING-FAN-KIT-MPG-HP-/161117605123?pt=Motors_Car_Truck_Parts_Accessories&hash=item25835b8d03&vxp=mtr

Some one already put a fan kit together for the CRD.

those claims seems pretty awesome, I wonder how true they are.

I know one of the first mods people do to the Chevy Trailblazer SS is efan conversion. They pull the fans from a 4th gen Camaro and its a direct plug in. All you have to do is enable the fan speed tables in the ECU and its all controlled just like it came that way from the factory. Guys are getting 15-20hp to the wheels with just the fan swap.

Brianawd · **Joined:** Wed Apr 03, 2013 12:59 pm **Posts:** 130

mass-hole wrote:

Brianawd wrote:

http://www.ebay.com/itm/JEEP-LIBERTY-CRD-DIESEL-FF-DYNAMICS-EXTREME-ELECTRIC-COOLING-FAN-KIT-MPG-HP-/161117605123?pt=Motors_Car_Truck_Parts_Accessories&hash=item25835b8d03&vxp=mtr

Some one already put a fan kit together for the CRD.

those claims seems pretty awesome, I wonder how true they are.

I know one of the first mods people do to the Chevy Trailblazer SS is efan conversion. They pull the fans from a 4th gen Camaro and its a direct plug in. All you have to do is enable the fan speed tables in the ECU and its all controlled just like it came that way from the factory. Guys are getting 15-20hp to the wheels with just the fan swap.

Not sure on the #s the guy has. But you will for sure free up some Hp as the fan is a big drag on the motor.

The guy who builds the kit is on the crd facebook page. You could ask him some questions.

I plan on ordering the kit after the 1st of the year.

dieseldoesit · **Posted:** Tue Oct 08, 2013 2:12 pm

So who is going to buy this kit and let us know if the gains are real?

thermorex · **Posted:** Tue Oct 08, 2013 2:51 pm

Yea, that's a neat idea. The only thing I don't like is that the fan shroud is secured by the radiator. The biggest electric fan for vehicles that I know of is 16 inch. That fan has a pretty big torque when it starts and in time, my fear is that it will cause radiator leaks due to strains/tensions. But that's not a show stopper since some thick brackets can be made to secure the shroud on the upper cross bar. Regardless, a variable speed controller should be used since it's smoother on electric system (it starts smoothly at 60% then as temp goes up, it reaches up to 100% speed). Definitely a good idea though, especially for offroading but not that good for heavy towing imo, the mechanic one can pull better cfms on higher rpm.

thermorex · **Posted:** Tue Oct 08, 2013 2:55 pm

dieseldoesit wrote:

So who is going to buy this kit and let us know if the gains are real?

I plan on doing the mod anyways, but it may take about a month. And since I don't tow too much(and only couple thousands lbs on short distance), I bet the gains are real and I won't have any heating issues, I gained 1 mpg at my Cherokee going with electric fans and Cherokee has a smaller mechanical fan with less drag.

flash7210 · **Posted:** Tue Oct 08, 2013 3:12 pm

You guys are aware that the CRD already has an electric fan, right?

I removed my mechanical fan over a year ago. Using only the stock electric fan.
Has not overheated once.
But I cant say my fuel mileage went up one bit. :roll:

Brianawd · **Joined:** Wed Apr 03, 2013 12:59 pm **Posts:** 130

Once I have some extra funds I will order the kit.

Yes I do know we have a fan in the front. I my self have thought about using just that fan. But its only a auxiliary pusher fan. I would much rather use a over sized puller fan.

My plan is to pull the mechanical fan and the auxiliary pusher fan and use only the kit fan. by pulling the auxiliary fan it will give me room to install a new intercooler.

thermorex · **Posted:** Tue Oct 08, 2013 4:57 pm

I am aware of the front electric fan, I lost it when I installed a huge transmission cooler and replaced it with 2 7inch fans. The factory electric fan starts when the engine temps are a little to high, plus being a pusher is not so efficient as puller.

Whats funny is that I was just skimming through summit racing magazine and I found this:

The bad is the 20x20 inch shroud we need comes set for a 14 inch fan, so some cutting for a 16 inch would be required.

On the other hand, shroud plus fan would be just a little bit cheaper than the eBay one (250-ish, plus shipping, switches, wires relay etc), it may not even worth the hassle...

thermorex · **Posted:** Wed Oct 09, 2013 12:05 am

Just FYI guys, I asked the eBay seller for a price just for the fan and shroud and brackets and he lowered the price to 220+40 shipping. I will use a variable speed controller of my choice. So far the eBay seller seems pretty cool.

arengant · **Posted:** Wed Oct 09, 2013 4:23 am

thermorex wrote:

Just FYI guys, I asked the eBay seller for a price just for the fan and shroud and brackets and he lowered the price to 220+40 shipping. I will use a variable speed controller of my choice. So far the eBay seller seems pretty cool.

Wow glad I found this! What controller would you choose? I might order this soon.

thermorex · **Posted:** Wed Oct 09, 2013 9:23 pm

arengant wrote:

Wow glad I found this! What controller would you choose? I might order this soon.

I already got it a while ago, as a spare for my Cherokee that already has e-fans, so I have it. I got it from summit:

http://www.summitracing.com/parts/flx-33054/overview/

And I can say I love it on the Cherokee. It starts very smooth, you hear the noise it makes and after about 3 seconds, fans spin at 60%, then, if temperature increases it goes gradually to 100%. You don't need any other relay either, that box does all the magic. The probe I zip-tied it on the radiator with 2 thin ties, didn't want to break the fins by mistake. You can also put a switch to cut the power to the controller when going through water. The controller is also adjustable, so you can make it start sooner or later.

thermorex · **Posted:** Wed Oct 09, 2013 9:31 pm

Brianawd wrote:

Once I have some extra funds I will order the kit.

Yes I do know we have a fan in the front. I my self have thought about using just that fan. But its only a auxiliary pusher fan. I would much rather use a over sized puller fan.

My plan is to pull the mechanical fan and the auxiliary pusher fan and use only the kit fan. by pulling the auxiliary fan it will give me room to install a new intercooler.

Btw, just realized you wanna take the pusher away... Your ac wouldn't cool enough to have comfort in the car when is hot outside. It happened to me, little under 100 in Alabama this year, I took out the pusher to install a big transmission cooler and I replaced the pusher with 2 7inch fans, the only way I could fit the cooler with some fans. As a result, my ac barely made 70 degrees(with both little fans running) after the car sat on sun for almost one hour, you should be aware of this and only take out the pusher if you feel comfortable with warmer ac...

Electric vs Mechanical fan cfm

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