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Mechanical fan CFM?

M

mrtosh

NAXJA Forum User
Location
Woodbury, MN
Does anybody know how much CFM the stock mechanical fan pulls at idle(warm/cold)? I'm looking to maybe go another route for my tranny cooler but am wondering if the stock fan clutch will pull more CFM.

TIA guys,

Sean
 
02-05-2009
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BS Fab 'Fo Life...
Join Date: Mar 2006
Location: Riverside/Running Springs, Ca
Posts: 3,365


Re: 2 Factory electric fans
The problem in doing so is that the stock mech fan pulls about 4K CFM where as our e-fans pull around 2K ( a little less IIRC) So by pulling your Mech fan in place of a stock on your losing roughly 2K CFM in the process...

Heres a good little discussion on it that I found. http://jeephorizons.com/phpbb/viewtopic.php?t=13510
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Look for a 2 speed fan from an early 90's V6 taurus or lincoln mark 8 at the junk yard

It'll have 3 wires coming out of it, and the fan is centered in the shroud, the offset 3 wire fans are just over 2000cfm, the right one out of a taurus is over 4000cfm on "high".

Alot of the muscle car guys use them since they take up very little space and are quite powerful for an e-fan.
 
mrtosh said:
All great on the elec fan side, but I'm wanting to know what the mechanical viscous fan pulls at idle.
Click to expand...


I am not sure if I ever saw that information. All I remember seeing kicked around is 2,000 to 3,000 CFM and that is the maximum I beleive. Maybe some with the proper test bench will test this and put out the numbers.
 
Wow, what a question!

Ok, what are the elements here?

Fan size, blade width, blade pitch are all variables. If we pick a 4.0 in a 1990 Renix Xj, then the fan can be measured along with numerous other variables. It is reported that a stock thermal viscous fan runs, at temperatures of 170 degress and higher (engaged) at 60 to 70 percent of shaft speed. So we need to know the idle RPM, water pump pulley RPM, size of the water pump pulley and the diameter of the water pump shaft.

Once all of the above has been determined all we will need is an engineer or the guy from the Numb3rs TV show to figure out the formula.
 
I have a mark VIII 2 stage fan. In the research, the lincoln fan has a higher cfm and uses less amperage.

Personally, I'm holding off on the mod until I upgrade to the 120 amp alternator.
 
the below quote taken from http://www.go.jeep-xj.info/HowtoElectricFan.htm third paragraph

Now the mistake that many have done when they tried to replace the mechanical fan with an electric one is that they have used too small a one with a lower CFM rating than the mechanical one. I spoke to the company that built my custom 3 row radiator and he stated that our XJ's need a CFM rating of 2000 minimum to do the job and around 3000 CFM if towing a lot offroad to replace the mechanical one along with the standard electric one.
Click to expand...
 
I understand it's kind of a off the wall question, but I'm looking to do a remote mount fan mounted cooler for my transcooler(400cfm) and was wondering if the stock viscous fan would pull more than that at idle when crawling on the trail. I did run a stacked plate B&M 70268 that is commonly run and it worked great going down the road and mild traffic, but on the trail it didn't cool all that great.
 
mrtosh said:
I understand it's kind of a off the wall question, but I'm looking to do a remote mount fan mounted cooler for my transcooler(400cfm) and was wondering if the stock viscous fan would pull more than that at idle when crawling on the trail. I did run a stacked plate B&M 70268 that is commonly run and it worked great going down the road and mild traffic, but on the trail it didn't cool all that great.
Click to expand...

I too have one of the same Stacked Plate cooler and find its performanance is not quite what I expected. In addition, I think it is the reason my XJ get hot when cruisng 80+ MPH. It blocks too much of the radiator;... coupled with the fact that I have no mechanical fan and very large disc looking motors for the electric fans. My question to myself is 'Where to mount another cooler on a DD / weekend warrior?'

I am seriously contemplating going the Go-Jeep route replacing the Derale's (DER-16928 from Summit) twins I have for the Taurus and OEM new style electrical fans and mount the oil cooler behind the cross member. I think for an XJ with a manual transmission, the Derale would be perfect. I think if space was available, a fan mounted oil cooler with its own thermostat switch would be the perfect solution.

To answer your question, it dosen't appear there is anyone who have good information regarding the CFM at various speeds of the OEM mechanical fan. It would be nice to know even if it is just FYI.
 
My plan is to mount the tranny cooler in the spot that gojeep put his, but to use a fan mounted cooler. Derale makes one that will work great part #15830. I just don't want to inhibit engine cooling and want to get the most out of my tranny cooler.
 
I would think that getting the trans fluid out of the radiator would lessen the load on your cooling system, even if a separate trans cooler and fan are pushing hot air towards it- there's still some physical separation, which should mean less heat transfer than the incorporated cooler in the radiator, right? If you're planning to use both coolers in series, I'd think it would still be less of a burden on your cooling, since it's more surface area, and more CFM across it, for the same amount of fluid moving through either system.

If that sounds stupid, someone will likely chime in and debate that...
 
Last edited:
mrtosh said:
My plan is to mount the tranny cooler in the spot that gojeep put his, but to use a fan mounted cooler. Derale makes one that will work great part #15830. I just don't want to inhibit engine cooling and want to get the most out of my tranny cooler.
Click to expand...

if you install a trans cooler in the same location that go-jeep did, then its not even going to be covered by the stock mech fan. if you wanted to leave your stock mech fan, you could put a trans cooler behind the crossemember (like go jeep did) and run an independently controlled e fan to it without much worry.

techno1154 said:
I am seriously contemplating going the Go-Jeep route replacing the Derale's (DER-16928 from Summit) twins I have for the Taurus and OEM new style electrical fans and mount the oil cooler behind the cross member. I think for an XJ with a manual transmission, the Derale would be perfect. I think if space was available, a fan mounted oil cooler with its own thermostat switch would be the perfect solution.

To answer your question, it dosen't appear there is anyone who have good information regarding the CFM at various speeds of the OEM mechanical fan. It would be nice to know even if it is just FYI.
Click to expand...

i went the route of go jeep and all has been well. i have a taurus fan mounted vertically with a large trans cooler behind the front crossmember. i still have a little gap left to the side of the trans cooler and its blocked off for now. when i do some steering upgrades i will put a stock trans cooler in there for the ps pump. i have a DCC FK60 controlling my taurus fan and i have not heard my stock e fan kick on for quite a while.
 
Stewie, What cooler did you use?

I am a little bit turned off by the 'staked plate' type. I thing the tube and fin type may be better but I have no data to support my assumptions.
 
Stewie I understand the mechanical fan won't cover the area where I want to put the cooler. If you look at the part number I listed its for the fan mounted econo cooler. I think it should be more than sufficient for the tranny while wheeling.
 
Techno from what I've read the stacked plate cools Better(this is coming mostly from the people who use the stacked plate though). Wish I could link the cooler I want to use from summit. If you do a search of that part number it should come up.
 
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