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OEM Mechanical Fan Retrofit

47K views 72 replies 25 participants last post by  BillyT 
#1 · (Edited)
Off road, and in stop-n-go traffic, the cooling fan on the JK comes on to cool the radiator when the water temperature reaches 215°F. It brings the temperature down to about 195°F, and turns off. The cycle continues until there is sufficient air flow from forward movement to keep the water cool without the fan.

There’s nothing so bad about that from the engine’s point of view.
However, until the fan comes on, things in the engine bay can get quite hot, including intake air temperature. The automatic transmission fluid temperature will also climb during the time the fan is off, even if there is an aux cooler installed. The aux cooler may prevent the transmission from overheating, but the fluid temperature can still get quite high when compared to the temps with sufficient forward movement.


I have been monitoring the temperatures of the engine, transmission (with an aux cooler), and intake air. The engine takes air from the engine bay, so I’m using intake air temp to reflect the approximate engine bay temperature.

With all that in mind, I decided it was time to cool everything down a bit.
The only item I could think of that would address all of the temperatures listed above is a fan that turns all the time the engine is running.

I thought about adding a switched ground wire in the fan high speed relay circuit. That would work, while off road and in traffic, but the driver would have to remember to turn it on, and off when on the road. How long will the electric motor last with the extended run time?

The idea of a mechanical fan seemed like a good idea. There would always be air flowing through the transmission aux cooler, the A/C condenser, the radiator, and the engine bay. It seemed ideal.

After a little research on the forum and elsewhere, I came up with all the parts to convert from electric cooling to mechanical cooling, (kind of retro, I know).
The fan and shroud are specifically designed for the pre-2012 JK. There is also a MOPAR fan clutch available for the JK, but it’s over twice the price of the generic clutch. If there is a longevity issue, I’ll try the MOPAR fan clutch.
Everything in the photo below is an easy plug-n-ply installation. It took about 1 hour from opening the hood to driving off for an ops check. Like I mentioned, it’s all designed for the JK. The stock electric fan comes out. The new fan and shroud go in.


For now, I’m going with the mechanical fan and shroud. There is also an electric fan designed to work with the shroud, for added cooling in extremely hot locations. The mounting points for it are on the stock radiator frame. The JKs shipped to the Mideast have the electric fan, shroud, and mechanical fan.
I don’t think the additional electric fan is necessary for the U.S. But, the option is there for those who want to have a lot of extra cooling capacity.


The mechanical fan and shroud have been installed for only a day, so I can post only preliminary results.

There is additional noise when the engine is first started. Once the fluid in the fan clutch moves to the proper chamber, it quiets down to nearly stock. On a cold start, it takes about a minute or two. On a hot start, it takes about 30 seconds.
The temps here have been in the 60’sF.
I’ll list the vehicle’s temps under similar conditions before and after the conversion. These are off road and in-town traffic conditions. There is no real difference on the highway, as there is plenty of air from the forward movement.
Edit: Since I wrote the preceding sentence, I have learned the automatic transmission stays cooler on the highway, too.
My theory is, the fan creates a low pressure area behind the radiator, which allows more air to flow through the cooler, condenser, and radiator.

Before, the engine temp would cycle up and down between 195°F and 215°F
After, the engine temp stays at 195°, ± a few degrees.

Before, the trans temp would climb to about 140°F.
After, the trans temp stayed below 120°F.

Before, the intake air temp would climb to 165°F+.
After, the intake air temps stayed below 115°F. (I’m assuming this also indicates lower engine bay temps.)

Before, opening the hood following a moderate idling period, there seemed to be a lot of heat in the engine bay.
After, opening the hood following a moderate idling period, the heat seemed to be a lot less, and there was a nice breeze blowing over the engine from the fan.

Before, overall average gas mileage was around 18.5 mpg.
After, (well, it’s too soon to tell).

The parts involved:



The fan installed on the water pump:



The finished product:



Photo of the stock fan, and the fan used with the mechanical fan and shroud, if max cooling is needed:
 
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#3 ·
before, the intake air temp would climb to 165°F+.
After, the intake air temps stayed below 115°F. (I’m assuming this also indicates lower engine bay temps.)
thats interesting, first time I've seen someone post intake temps here. I also monitored mine with the aeroforce gauge and with my river raider snorkel I never ran more then 10 degrees above outside temps for my intake temp. I guess that was the truest thing to a cold air intake.

I like the mechanical fan set up :cool:
 
#4 ·
There is no ideal fan, only compromise. Engine driven fans have come a long way in the last hundred years. I just saw a fixed pitch steel 2 bladed fan on an early 4WD truck from the teens in a wrecking yard. There are flex fans, viscous fans, thermal vicious fans, electro mechanical fans, clutch electo mechanical fans and more....Each designed to achieve the goal of keeping the engine cool.

Of coarse modern engines demand efficiency as well as performance, this has taken a bite out of the engine driven fan on light duty vehicles.

Two big concerns with engine driven fans is they are usually dependent on water pump speed, notice I did not say crankshaft rpm. This does allow some tuning of fan hub speed. Two, engine driven fans have the ability to move a lot of air, this was good 50 years ago when engines ran 180* and gas was 30 cents a gallon. Controlling fan output independent of engine speed could lead to inefficiencies.

Cooling an engine at low rpm with heavy loads and a/c on, such as when rock crawling in the Southwest is challenging. Remember even if engine temps are low the a/c condenser pressure must be dealt with. Jeeps literature regarding Diesel JK's with engine driven fans suggest keeping engine rpm elevated at low speed and turn the a/c off. It can be tough to drop a gear or two to raise rpm's while crawling.

Later generation engine driven fans have tried to address this dilemma in different ways. Of coarse the thermal fan clutch. How about a hydraulically controlled fan? The Japanese did this for years in their luxury cars. The Germans were big on a electro clutch which would disengage the fan when not needed. So on a cold start the fan would disengage right? Oops the operator turned on the a/c, now what? Engaging the mechanical fan uses a lot of energy. Well lets add an auxiliary electric fan. BMW and Mercedes still do this. To have the air moving capacity of an engine driven fan and the efficiency of electric fan has been popular lately, like in 1/2 ton American trucks. GM ran the notoriously unreliable electro mechanical fan clutch on the Trailblazers and Envoys. A digital signal from the ECM and an rpm sensor would engage the engine driven fan to what was needed.

The next generation of half ton trucks is ditching the engine driven fan and going with enormous electric fans, sometimes two. Why?

Electric fans are very controllable, they have evolved as much as engine driven fans. Electronic fans are independent of engine rpm, this means they can provide maximum airflow at low speed and low rpm when it is needed most. One important consideration is water pump flow rate. In the early days we would overdrive the w/p so the coolant could circulate at 5-600 rpm crawling off road. Modern w/p's have good low rpm flow.

2 speed and variable speed electric fans can remain off on the highway, full blast in stop and go traffic and somewhere in between when required. The Ford/Lincoln 2 or variable speed fans are my favorite, they can move in excess of 5,000 cfm and idle at low speed. This is where the gas JK falls; the simple 2 speed ECM controlled electronic fan. Does a good job keeping the engine and a/c condenser happy.

Some issues with electric fans. High powered electric fans use a lot of current, they must be staged through a series of relays or a fan control module which always seen to fail. A Lincoln fan started from a dead stop can draw over 100 amps, this puts a huge load on the circuit. In deep water crossings unsealed fan motors are susceptible to contamination. Having a fan cut off switch is nice. DC motors can run under water, it is the dirt and debris that act as conductors and contaminate the motor.

Other considerations for the JK are moving air through the engine compartment. The JK has sensitive modules under the hood. Adding a SC or V8 reduces area for air to move through. In our swaps we keep the coolant bottle and air intake small to promote airflow. Of coarse adding large coolant bottles, dual batteries, cold air intakes, hydraulics, etc.....restrict airflow.

Trying to pull air from an area of low pressure to an area of high pressure is a battle. Under the hood of a JK with a Hemi there is not place for hot air to evacuate, a high pressure zone is created and very powerful fans are required to overcome the pressure imbalance. I have measured under hood temps over 300*. An engine driven fan would be in my choice here. Cutting holes in the hood or removing the fender liners are helpful. It is simply a situation where design is important, air flow critical.

Here in the Southwest we have fought the JK overheat battle with V8 and SC JK's in temps over 120* Hot wiring a fan on or cutting holes is not my preferred method.

I like what the OP has done here. It is genuine way of adding airflow. He may need to add an electric fan if he ever comes out to Death Valley and crawls. He may see a slight effect on mpg. I wouldn't worry too much about w/p wear, they are designed for it. One thing I will say is OE fans are a step above. We won't run aftermarket thermal fan clutches, they are less efficient, not balanced as well which leads to w/p wear and do not cool as well. In a cool environment I would stay with the stock electric fan and add an evacuation fan to promote low pressure under the hood which draws in cool air. Effectively it is achieving the same goal as adding an engine driven fan to constantly pull air into the engine compartment.
 
#5 ·
Cars come in the Middle East with the mechanical specifications of electric fan at the same time .


That we do here is to remove the mechanical fan and keep the electric fan only with summer temperatures reach 125 +

and there is no problem remove them , some cars come 100k miles

In fact, remove the fan power increase by almost 10 hp Dyno and less fuel consumption significantly !!!

I do not see any reason to keep mechanical fan with an electric fan ,acc most owners of old cars are trying to change the mechanical to the electric fan to increase power and save fuel.

I think that the mechanical fan is important in the case of unit diameter at a load of great distance in the heat too!!!i tried to pull 33" boat with no problem !
also When you load the jeep large loads , that's why most of the trucks come in mechanical fan and this not ganna happen with not pleace for loading :)
 
#6 · (Edited)
I'm keeping track of fuel consumption. It's looking like it won't be much different from before the conversion. I'm sure it will use more fuel, but it won't be a lot more.

I like the way it is keeping things a lot cooler, especially the transmission and computers.

The hp loss to the fan will be a lot less at normal driving speeds.
I suspect the 10 hp as logged on the dyno is at the top of the graph.
Normal driving for me is usually between 1500 and 2500 rpm.
 
#7 · (Edited)
Nice write up and I see what you are trying to do. I just can't see myself making my engine work harder just to keep it a little cooler. Also when running the AC the electric fan runs on high constantly so for me here is Arizona with 100+ temps everyday of the summer I usually have the A/C blowing in my face and my temps read just as yours do with the mechanical fan. Minus the parasitic drag caused by the mechanical fan.

Also another thing to remember when doing this conversion is that when you forge water you will want to stop that mechanical fan from moving! Seen a few fans spin right into the radiator that way.
 
#8 · (Edited)
Nice write up and I see what you are trying to do. I just can't see myself making my engine work harder just to keep it a little cooler. Also when running the AC the electric fan runs on high constantly so for me here is Arizona with 100+ temps everyday of the summer I usually have the A/C blowing in my face and my temps read just as yours do with the mechanical fan. Minus the parasitic drag caused by the mechanical fan.

Also another thing to remember when doing this conversion is that when you forge water you will want to stop that mechanical fan from moving! Seen a few fans spin right into the radiator that way.
There is no doubt the electric fan works, when it's on.
I've noticed on mine, the electric fan is not on all the time the A/C is on. If yours is on all the time you are running the A/C, it's probably because you are trying to get rid of a lot more heat than I am here in Maine.
So, when my electric fan was not running, (I don't use the A/C all that much), the transmission and under-hood temps, including intake air temp, were climbing quite high, compared to when the fan was on.

So far, I see only benefits. It's an interesting experiment.

Forging water that deep isn't something I'll be doing on purpose.
There is almost a foot of clearance between the fan and radiator. That's why the shroud is so long. (I haven't actually measured it, but it seems like a lot of room.)
 
#10 ·
If I was trying to increase efficiency in cooling at this point, i'd source a larger capacity radiator, I think the OE is still only two pass. I'd have a three pass made and i'd add an auxillary pusher fan with switch and t-stat. You would not have to worry about temps again.

I like the write up and I did ponder this very thing when I first got my JK. Cooling is a major concern here in AZ.
 
#11 · (Edited)
I wasn't worried about the stock radiator's ability to cool the engine.

My aim is to increase the air through the transmission cooler, A/C condenser, radiator, and on through the engine bay in general, keeping these things and everything else under the hood a lot cooler.

That's exactly what I have observed, starting with the first drive after the mechanical fan was installed.

Testing still in progress; waiting for the weather to get hotter.
 
#12 ·
btw

if your jk 07-10 you can control the electric fan for many Options when ( start-off )

1- low speed
2- high speed
3- with A/C on

by CMR
DiabloSport u7137

I Tested that and its work very good with LX body add JET 180 degree thermostat
the fan start from 180

but not sure about jeep ( not testing yet ) Diablo says its same have anyone tried ?



http://webcache.googleusercontent.com/search?q=cache:e5bsPiKbljoJ:www.towingpowerproducts.com/p-6565-diablosport-predator-programmer-u7137-jeep-grand-cherokeewranglercommander.aspx+&cd=4&hl=ar&ct=clnk&gl=sa
 
#13 ·
... i "could" be wrong in this... but i've been under the impression that my oem fan comes on in low speed when the a/c cycles... and high when the engine temp gets up high enough. again. i could be wrong. ...anyway...


as for keeping an electric fan in conjunction with a manual fan. only newer designs such as the '08 expedition i drive at work had a computer controlled fan clutch. its engine driven and same general theory as the one mentioned here, however, there is an electronic engagement that kicks in with the a/c.

if there isn't enough airflow through the a/c condensor, then the a/c can overpressurize... and malfunction. the a/c operates independent of the coolant temp, so there in lies the need for an aux fan. look on older designs and its the same theory. the geo tracker/suzuki sidekick is like this if it has a/c.
 
#17 ·
That makes sense now, thanks. I couldn't tell what I was looking at from the picture the parts guy showed me.
Here's the quote I received back from a dealer over here in Oz.
Fan blade $104
Fan motor $488
Bracket $445
And they wonder why we try so hard to import our own parts from the US
 
#18 ·
GCC Spec (Middle East) JK's come with a factory engine driven fan. I am not convinced at their performance.

I just sold my 09 JK and am importing a 12 JKU from BOR. Dan at BOR is building me a 6.4 SRT8 Hemi with dual electric fans and a Griffin radiator. There will be a primary engine fan (variable speed depending on heat thresholds) and a 12" Pusher fan on the front of the radiator if I encounter extreme heat issues. This paired with a TMD hood, Dan is 100% confident I will not have any issues.

The beauty of the TMD hood is the active cowl intake that routes cool air from the hood to a sealed CAI on the passenger side of the engine bay. This works for me as 95% of my off-road adventures are overland and high-speed dune bashing. Rocks are not a big deal in Dubai but, we got SAND... LOTS OF SAND!

-Phil
 
#26 ·
Ronjenx this is the type of stuff I enjoy reading. Nice job!
I have an 07 4door with the Ripp supercharger and my under hood ambient temps have gotten so high that optima batteries have failed. I removed my inner fender liners and installed an AEV hood to help with air flow. Unfortunately where my transmission cooler is mounted "auto conversion" with the intercooler in front of the radiator ... I am not able to put a mechanical fan in that area. I will be watching this thread. My trans temps have been close to 220 at times and typically run close to 200 on the street. I have the large B&M cooler with a fan. I did notice what seems to be a substantial difference in under hood temps with the AEV hood. I do have the Aeroforce gauges but I did not document pre/post readings. Curious to see the temps with your setup including transmission when it gets in the 90's
 
#29 ·
It's funny, I was just having a conversation with a tech at work about the hot oil message. I said I was gonna install a cooler and his response was "why, the fan will still only come on at a certain temp. You should just install a mechanical fan, then it will be on all the time. It will bolt right on."
The only this holding me back, was the cost of the factory fan clutch, but now that there is cheaper option, I will probably do this. I'll be following your results.
 
#30 · (Edited)
A cooler is still a very good thing to have for the automatic transmission.
I find it interesting that my transmission temps are lower even on the highway where one would think there is naturally enough air flow through the grill.
My theory is the mechanical fan creates a much lower pressure area behind the radiator, allowing more air to flow through the aux cooler, A/C condenser, and radiator.

Regarding the cheaper Car Quest thermal fan clutch, I have no idea if its quality equals the OEM thermal fan clutch. There's no telling how long it will take to find out. It's working very well for now, though.
 
#33 ·
What year(s) did the JK come with a manual fan? Was it only on JK's equipped with automatic transmissions? Mine is an 07 manual and it has only the electric fan. I don't have any cooling issues but I also don't have any gauges to read temps either. I've had all the fancy gauges and computers on previous cars and all they did was cause me to stare at them all the time monitoring for potential issues. I like being blind now. :)
 
#34 ·
What year(s) did the JK come with a manual fan? Was it only on JK's equipped with automatic transmissions?
None in North America...
The JKs shipped to the Mideast have the electric fan, shroud, and mechanical fan.
I don’t think the additional electric fan is necessary for the U.S. But, the option is there for those who want to have a lot of extra cooling capacity.
 
#35 ·
As pointed out in the first post of this thread, my long term overall average mpg has been 18.5.

I have filled up twice since the mechanical fan conversion. Both tanks were mostly around town and some 50 - 55 mph non-interstate roads.
The first tank calculated to 0.5 mpg less than average, and the second tank calculated to 0.1 mpg above the average.

The first tank was lower by a comparatively larger amount probably because I spent quite a bit of time monitoring temps sitting still, idling, and otherwise seeing how the fan behaves.

I'll update again after two more tanks. It's looking good so far.
 
#36 ·
The weather hit the 90's today, so I did some testing of the mechanical fan conversion on the trail in 4wd.

In 4hi, during most of the slow ups and downs of the trail:
The water temp hovered right around 195°, once in a while hitting 198°.
The transmission temp hovered around 130°, spiking once or twice to 135°.

In 4hi, up a steep ¼ mile climb:
The water temp remained in the mid 190's.
The transmission temp hit 170°, and never went over. That was with a lot of torque converter slippage, because the speed didn't allow it to lock up.

I repeated the runs shown above in 4lo. The water remained in the mid 190's, and the transmission temp remained about 140°.

As we all know, 4lo really lightens the load on the transmission and torque converter. The torque converter even locked up on the lighter stuff.


I was also running the A/C at different times during the test. It operated well, and had no effect on the water temp.
 
#38 ·
How are your temps at low speed(like stop and go traffic) when the electric fan would normally come on? Are they still better with the mechanical? Have you had any unusual codes set from the PCM expecting the electric fan to come on, but doesn't? I'm trying to decide if I want to have both fans or just the mechanical.
 
#39 ·
All the temperatures are lower in stop and go traffic, and while off-roading.

I have also noticed the transmission temp is lower on the highway, likely because the mechanical fan creates a low pressure area behind the radiator, allowing more air flow through the grill, cooler, A/C condenser, and radiator.

I have had no warning lights, and no active or pending codes.
I presume it's because the mechanical fan keeps everything below the electric fan request threshold, including the A/C fan request threshold.

So far, I have not seen a need for the additional electric fan. In a hotter climate, it may be necessary.

One thing I am debating is whether or not to get the MOPAR fan clutch and install it. The Car Quest clutch seems to be working, but I would like the additional data the MOPAR clutch would provide.
 
#41 ·
The average of my first 5 tanks of gas after the mechanical fan conversion is 0.5 mpg less than the previous 4 year all-time average.
Is it the fan? Time will tell.
Monitoring mpg will continue.

In the meantime, I'm seeing lower temps under the hood, on and off road; transmission, engine, intake air, etc.

Now, it's a matter of waiting to see how things behave next winter. I have a feeling the transmission will still get up to the required 80°F with no problem.
 
#42 ·
Good information, thanks for the testing.

1/2 mpg probably means a lot to the manufacturers and CAFE standards. But I would say it is a fair trade for lower temps.

Wear on rubber parts like belts and hoses as well as the electronics could make up for the additional fuel used.

Your transmission has a transmission temperature sensor in the TRS and has some control ov er transmission temps through the TC and clutches. Besides the stock JK trans cooler is a joke.
 
#43 ·
Ron, where are you measuring your transmission temps? At the torque converter, in output line to the cooler, or in the pan? Just curious because I was using my Superchips to check my temps and had wildly higher transmission temps. I'm assuming SC is measuring the sensor inside the TC, but still the temps were concerning - even with an aux cooler (but still running the electric fan).
 
#44 ·
I am reading the sump temperature with a AeroForce gauge through the OBDII plug.
I also have a probe in the pan with a regular gauge on the A pillar. The two agree within a needle width.

I believe your Super Chips reads the OEM sensor in the sump, too.
 
#45 ·
I'm on tank #9 since the mechanical fan conversion, and still at ½ mpg less than the long term average.
The weather has been in the 80's and 90's.
Engine temp still hovers around thermostat temp.
Transmission temp remains in the 90°F to 130°F range.
This is in city stop-n-go traffic, on the highway, and on the trail.

Normally, the fan runs at around 30 percent of pulley speed.
There have been a few times when the thermal clutch has stepped the fan up to 80 - 90 percent of pulley speed, but the temp gauges have been steady.
 
#46 ·
Update on transmission temps with the cooler weather:

The local temps have been in the 20'sF in the mornings, lately. My transmission has had no problem reaching the 80°F mark, which is where normal shifting commences. It continues to run in the 90°F to 130°F range.
 
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