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Writeup: Replacing the Mechanical Fan w. another OEM Aux Fan

comanche91

NAXJA Forum User
I have been wanting to dump the antiquated mechanical fan for a while now on my MJ, and have been looking at various "how-to's" on Dino's and Gojeep's websites, among others. One criterion I had was that I wanted to keep it restorable if I ever wanted to go back to the mechanical fan, so I did not want to cut the existing mechanical pulley shaft as Gojeep did, which was necessary for clearance using the large 16" fans. After looking at various installs, I decided to go the route Slo-sho did and replace the mechanical fan with another XJ/MJ OEM electric aux fan, but with a few mods. These fans pull a lot of air for their size and I had a couple of spares readily available. Step one of course is to remove the radiator and the old mechanical fan blade, shroud, and clutch. Then I replaced the fan pulley studs with 5/16" x 24 x 3/4" bolts for added clearance as shown below.

fan1.jpg


I used the bottom radiator brace for mounting the new fan. In the pic below, in order to make the new aux fan fit and clear the mechanical fan pulley, I had to Dremel two new slots in the radiator bottom support plate to move the fan closer to the radiator, and about 2" toward the driver's side so the fan blade head would clear the pulley bolts better.

fanmod1-1.jpg


This setup fits great, and the new aux fan shroud is very close (but not touching) the radiator which increases it's efficiency. Here's what the fans look like on the rad before mounting looking from the inside out:

fanmod2-1.jpg


After mounting, although it's hard to see, I have about 3/8" clearance between the pulley bolts and the new fan head. It's enough, but I will replace the hex head pulley bolts with lower profile button head bolts as soon as I can find them for a little added clearance.

fanmod5.jpg


Here's a back view of the two electric fans.

fanmod4.jpg


And a front view.

fanmod3.jpg


I used a Spal variable speed controller to independently control the new fan only, which is now my primary cooling fan. The LO speed is set to come on a 190*, and the HI speed at 215*. So far these settings are working fine, with the new fan staying on LO most of the time. The existing aux fan still operates as always, ON with the A/C or when the temp reaches 220* or so. But I did want redundancy just in case, so I wired in a dash switch so I could turn this fan on manually if the new primary fan went belly-up.

fan3.jpg


So far all is well, the new fan runs 90% of the time in LO, only coming on HI speed when stuck in traffic for some time. The existing aux fan has never come on (except when I run the A/C of course. I also have noticed a mile or two increase in MPG on the stroker, which helps. The engine seems to spool up faster too w/o because it's not pulling the old mechanical fan, but this may be my imagination. And changing either fan is now a 15 minute job. Hope this helps someone who is considering doing this mod.
 
I'm doing this conversion too, but am using an aftermarket 12" fan. It's my understanding that the newer curved blade design OEM fan pulls around 1000CFM and supposedly that's quite a bit more than the older straight fan design you put in. So you may want to keep an eye out for a cheap OEM fan w/ the updated design. It'd also be cool to flip the fan's roles and see if the "primary" runs any less. Then you'd know that the curved blade pulls more air.

My aftermarket is a 12" that pulls 1250CFM and only 10amps - I could never find a rating for the OEM, but I'd guess in the 8-12 range also. I'm also putting in a new all aluminum 2 core radiator, so hopefully my fan won't run as much, but I guess I'll know soon enough.
 
gone postal said:
I'm doing this conversion too, but am using an aftermarket 12" fan. It's my understanding that the newer curved blade design OEM fan pulls around 1000CFM and supposedly that's quite a bit more than the older straight fan design you put in. So you may want to keep an eye out for a cheap OEM fan w/ the updated design. It'd also be cool to flip the fan's roles and see if the "primary" runs any less. Then you'd know that the curved blade pulls more air.

My aftermarket is a 12" that pulls 1250CFM and only 10amps - I could never find a rating for the OEM, but I'd guess in the 8-12 range also. I'm also putting in a new all aluminum 2 core radiator, so hopefully my fan won't run as much, but I guess I'll know soon enough.

I originally had a Mishimoto 14" fan installed advertised at 1900 CFM. This was pure BS, the OEM fan pumps out at least 3x the air; the difference was very obvious. And according to a retired AMC/Jeep electrical engineer I know here, the square bladed OEM fan was conservatively rated at 1400 CFM, but it pulls 14-17 amps at HI speed depending on temperature, wgich I verified on a bench test. I plan to replace the square blade fan with a newer 1997+ model fan like the other one which pumps slightly more air, but this same engineer said the main reason for the redesign of the fan was to keep the noise down. The curved blade fans draw a couple of amps more too.
 
comanche91 said:
I originally had a Mishimoto 14" fan installed advertised at 1900 CFM. This was pure BS, the OEM fan pumps out at least 3x the air; the difference was very obvious. And according to a retired AMC/Jeep electrical engineer I know here, the square bladed OEM fan was conservatively rated at 1400 CFM, but it pulls 14-17 amps at HI speed depending on temperature, wgich I verified on a bench test. I plan to replace the square blade fan with a newer 1997+ model fan like the other one which pumps slightly more air, but this same engineer said the main reason for the redesign of the fan was to keep the noise down. The curved blade fans draw a couple of amps more too.

Actually you will also find some 1996s with the newer style fan, which means its slightly more likely you'll find one at a junkyard.
 
Excelllent write-up.....I'm seriously thinking to go this route. Any seat of the pants or should I say differences in "metered" (for lack of better words) engine temperatures?
Where can a spal contoller be purchased?

Ron
 
zluster said:
Actually you will also find some 1996s with the newer style fan, which means its slightly more likely you'll find one at a junkyard.

I'm pretty sure the 95-96 XJ fans had 8 curved blades; the 97-01 had 10. Trouble is the junkyards around here are asking $50+ for used fans. :shocked: Too much IMHO.
 
XXX said:
Excelllent write-up.....I'm seriously thinking to go this route. Any seat of the pants or should I say differences in "metered" (for lack of better words) engine temperatures? Where can a spal contoller be purchased? Ron

Actually, cooling seems the same as with the mechanical fan, running right around the thermostat temp (195*) as it should. But the engine is working less by not having to push the steel blades and it seems to wind up quicker. I got the Spal PWM controller on Ebay for $60 shipped, but I don't see any there now.
 
comanche91 said:
I'm pretty sure the 95-96 XJ fans had 8 curved blades; the 97-01 had 10. Trouble is the junkyards around here are asking $50+ for used fans. :shocked: Too much IMHO.

96's are a wierd year, there are some things on them that you can see they were getting ready for the 97 transition, one of them was the electric fan, another was the keyless entry, some lucky 96ers got the RF keyless instead of the IR.

Theres a couple of other things like that which are somewhat interesting.

But yes, some of the 96s got the latest and greatest from the factory.
 
That's cool, that's a lot simpler than I thought it might be. Been thinking about doing this, but I was expecting it to be more involved. I believe I read elsewhere that the mechanical fan takes as much as 12hp to run, but I have some trouble believing it's that much.

Anyhow, a quick search of Ebay turned this up.

http://stores.ebay.com/UNIVERSAL-PARTS-INC_SPAL-FANS-AND-ACCESSORIES_W0QQcolZ2QQdirZQ2d1QQfsubZ12QQftidZ2QQtZkm

<edit- bah, wrong link. Anyway, the controllers are near the bottom. 97+ Used fans are all $50 and up there too. Seems a bit high to me.>

OEM 97+ fan is 120, controller for 40... that's a helluva lot cheaper than any of the other conversion kits I'd seen.

Looking to free up a few more ponies, and also considering an APN header and a custom downpipe... might just have to pull the radiator while I've got everything else apart, and find my coolant leak while I'm at it. Glad I found this.
 
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gone postal said:
I'm doing this conversion too, but am using an aftermarket 12" fan. It's my understanding that the newer curved blade design OEM fan pulls around 1000CFM and supposedly that's quite a bit more than the older straight fan design you put in. So you may want to keep an eye out for a cheap OEM fan w/ the updated design. It'd also be cool to flip the fan's roles and see if the "primary" runs any less. Then you'd know that the curved blade pulls more air.

My aftermarket is a 12" that pulls 1250CFM and only 10amps - I could never find a rating for the OEM, but I'd guess in the 8-12 range also. I'm also putting in a new all aluminum 2 core radiator, so hopefully my fan won't run as much, but I guess I'll know soon enough.

Here's something interesting I found. The 12" Derale 16925 puller fan is rated at 2200 CFM. This fan has the same motor as the newer 97+ XJ aux fans (according to their tech support) but a different blade. So I'm pretty sure the XJ fans will pull at least 1600-1800 CFM, naybe more.

16925-large.jpg
 
Slo-Sho said:
I like the controller, is that a PWM unit? I have since added a group of relays which enables Hi/Lo speed by series/paralleling the fans to achieve the 2 speeds.

Hey Slo. Yes it is. They had them on Ebay a while back for $55, but don't see any now. Works great for LO and HI speeds, also can control another fan (ON/OFF only), but I'm sure you know the specs. Thanks for givin me the idea originally on the aux fan - it's the best way to go.

fan3-1.jpg
 
Just realized that egay store only sells the relays and wires- but you've got what, a programmable controller or something? I've never really fooled around with cooling systems other than maintenance stuff.

Got a part number for that thing, or a similar unit? Thanks.
 
hubs97xj said:
Just realized that egay store only sells the relays and wires- but you've got what, a programmable controller or something? I've never really fooled around with cooling systems other than maintenance stuff.

Got a part number for that thing, or a similar unit? Thanks.

All you really need is a thermostat switch, and a basic 12V relay. Just get a switch for 190-200deg and you'll be fine.
 
hubs97xj said:
Just realized that egay store only sells the relays and wires- but you've got what, a programmable controller or something? I've never really fooled around with cooling systems other than maintenance stuff. Got a part number for that thing, or a similar unit? Thanks.

It's called a Spal PWM (pulse width modulate) variable speed controller. Very versatile. Here's a link for the manual:

http://www.jaycorptech.com/tech/fan-pwm.pdf
 
Bryson said:
All you really need is a thermostat switch, and a basic 12V relay. Just get a switch for 190-200deg and you'll be fine.

Yeah, that's true, but the Spal PWM uses an existing temp sensor (either the gauge sensor or the ECU sensor in the stat head) and gives variable speed fan control so if you don't need the fan running 100%, it runs slower. It also handles fans up to 40A so you don't need a relay either. Using a relay and switch to control the fan you get either OFF or ON 100%.
 
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FAN-PWM.jpg


Part Number: FAN-PWM
Description: Automatic Programmable Fan Controller
Retail Price: $89.95

This water resistant controller is programmable, and will read almost all OEM and Aftermarket sensors on the market.

-Programmable to activate at any temperature
-Factory programmed to 160° Low, 200° High
-Variable speed for reduced fan noise
-Uses OEM or optional SPAL Temp Sensor
-Waterproof extruded aluminum construction
-LED indicators for High, Low, and A/C
 
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