How to install a Derale 20561 transmission cooler on your Wrangler TJ

With a recent series of serious overheating incidents while offroading and towing my little pop-up trailer, I decided to hasten my plans to install an auxiliary transmission cooler for my 42RLE automatic transmission. I had added one to my previous TJ that had the more robust 32RH, but Jeep’s newer automatic transmission like my 2004 Rubicon has is far fussier about such things.

High temperatures are the #1 killer of automatic transmissions. So, it makes a lot of sense to make sure it doesn’t overheat while towing trailers, rock crawling, offroading, or just plain crawling in heavy traffic on a hot day. How to do that? Add an auxiliary transmission cooler.

After much research, I decided on a stacked plate transmission cooler from Derale Performance, a well known manufacturer of cooling products for everything from engine oil to automatic transmissions. With over fifty years of making nothing but such products, it was clear to me that Derale knows what they are doing.

After viewing their catalog, it turns out that Derale Performance makes an automatic transmission cooler kit specifically made for the Jeep Wrangler, “Part # 20561 Direct Fit Remote Cooler, 87-06 Jeep Wrangler TJ, YJ.” Very cool, that is exactly what I need!

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You can purchase the Derale 20561 transmission cooler here.

Mounted to the frame, this type of fan-based stacked plate transmission cooler uses a thermostatically controlled switch to turn its 500 CFM fan on when the ATF reaches 180 degrees and off after it has cooled it back down to 170 degrees. No frame drilling or frame modification is required to mount it to the frame; it comes with a very cool two-piece clamp-style mount that makes the mounting process very simple. Derale says this kit can lower the transmission fluid temps by 30 to 40 degrees.

This is the box that arrived… you can see it is nicely packaged specifically for the Wrangler.

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It comes well packaged and it contains every thing needed to install it, down to zip ties for the electrical wiring. The only tools you need are minimal and very basic. If you have SAE size wrenches, a pair of pliers, wire cutters, and a solderless connection crimp tool, you’re good to go. A nice additional tool would be a heat gun and heat shrink tubing for the fan’s electrical connections.

It was engineered to be easily installed by anyone with basic hand tools and that’s what it turned out to be… a very easy non-technical job. The mount and fan frame are unique to the Wrangler kit so no mods are needed to get it to fit perfectly.

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Even the two supplied coolant hoses are already cut precisely to length and are complete with fancy red and blue anodized AN fittings. AN fittings are the standard for high-quality builds, you won’t have leaks from these.

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One of the first things I noticed about Derale’s kit was its set of instructions. It’s clear Derale put some serious time and effort into them. They are complete, extremely well illustrated, and leave nothing for you to have to figure out. Check them out below.

Derale Instructions: https://derale.com/images/stories/virtuemart/product/pdfs/20561.pdf

First things first, position the cooler on your workbench so you can attach its two fittings, install its thermostat switch, and do the very basic wiring so the thermostat switch can turn the fan on and off.

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Thread the aluminum fittings, the two on the left above, onto the fan assembly’s inlet and outlet connectors. Note that the o-ring shown above on the left-most fitting actually goes on the OTHER side of that fitting. The o-ring needs to be on the side of the fitting that threads into the cooler, not on the hose side as shown in the picture.

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Please don't beat me up too much for using the Crescent wrench on that 1 1/16" fitting, my SAE open-end/box-end set set only goes up to 1".

Attach the thermostat switch and its aluminum fitting as shown below using a 7/8” and 1 1/16” wrench. The thermostat switch’s sensor protrudes into its fitting far enough so it can actually touch the ATF as it is pumped through. Use a bit of Locktite on the middle of the thermostat switch’s threads to insure it doesn’t unscrew from the engine’s vibrations. Do not use a wrench to tighten the thermostat switch, it should only be firmly hand-tightened.

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The thermostat switch and fitting assembly is then screwed into the cooler’s input port.

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Wiring the thermostat switch in is easy, it is a simple on-off switch that turns the fan on and off based on the temperature of the transmission’s ATF fluid. The switch turns the fan on when the ATF reaches 180 degrees, well below the temperature where damage could occur to the ATF or transmission. The switch shuts the fan off after the ATF has been cooled back down to 170 degrees.

ATF can operate at 200 degrees without damage but much above that and it can become damaged. Synthetic ATF+4 can withstand a bit more heat but not much. The use of a transmission cooler can prevent your transmission from ever getting up into the danger zone of over 200 degrees. At 220, ATF begins to break down. As said above, heat is the enemy of an automatic transmission.

Note the following very carefully. MOST of the time, the black wire is negative and the colored wire is positive. In this kit, to get the fan to turn the right direction so it pulls cool air through the stacked plate cooler, the black wire is POSITIVE and the blue wire is NEGATIVE and it is the BLUE wire that gets grounded. Per the Derale instructions, simply read the label on the fan to verify which color is positive and negative so the fan doesn’t turn the wrong direction.

I used a bit of plastic wire loom to protect the wiring and then zip-tied it to an adhesive zip-tie holder to keep the wires where they belong.

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Next, connect the supplied red wire to the other side of the thermostat fan switch. This wire connects the fan to a +12v source. Derale recommends the +12v be switched, which means the power should only be on when the ignition switch is on. Derale provides an inline fuse holder and blade style fuse to protect everything. Slip the red wire into the provided protective plastic wire loom before mounting the fan.

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I cover every splice and every crimped connection with protective insulated heat-shrink tubing. Heat shrink tubing is inexpensive, better, and quicker than wrapping connections and splices with electrical tape. This pic shows a heat gun being used to shrink the heat shrink tubing that can be found in any hardware store, Home Depot, Radio Shack, etc.

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With the fan pre-wired and its hose connectors installed, it is time to install its mount to the Jeep’s frame. The top part goes inside, the smaller part slips over the frame from the outside.

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The mount leaves plenty of room for the fuel lines and wiring that run along the frame.

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The cooler is attached to the clamp with three bolts. Its angle can be positioned from flat to angled. Once it is at the angle you like, tighten the bolts. For me, it worked best by sliding the mount a bit further rearward and using the forward-most mounting bolt holes. It gives you a choice between two positions, the most forward position worked best for me.

The mount itself is well designed and purposely made from two gauges of steel. The heavier side securely holds the cooler to the frame and away from the fuel and electrical lines underneath. The other half of the mount is still a heavy-gauge steel but it is designed to provide a clamping effect when it bends slightly to conform to the frame and inside mount as the mounting nuts and bolts are given those final turns. The mount holds the fan very securely.

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For some, that position may seem to be exposed. However, it’s not as exposed as it may seem to be since it has the frame, skidplate, and control arm bracket on three sides of it. I will likely fabricate an additional guard to provide a little added insurance against a rock being in the wrong place at the wrong time. If this makes you feel better, I had my previous TJ’s on-board air tank in the same position and after nearly ten years on the rocks, the rocks never touched the air tank.

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The electrical line plus coolant lines are attached and tightened before the fan is clamped into its final position and passed forward. They are routed next to the frame and above the transfer case skidplate.

Coolant hose routing and connections
The two coolant hoses are routed along the driver’s side of the frame towards the radiator. The two hoses are connected to the radiator's transmission cooler output side, so the Derale system cools the ATF flowing back towards the transmission. Which side of the radiator's transmission cooler the Derale gets connected into, passenger-side or driver's side, depends on your TJ's model year and thus its transmission type.

For 2002 and older models which use the 3-speed 32RH or 30RH transmission, the Derale cooler lines connect to the passenger-side transmission output port of the radiator and the hard line the OE passenger-side hose used to connect to. Entirely remove the OE short hose that connected the passenger-side transmission cooler port to the hard line, connect the new Derale hoses to those fittings.

The current Derale instructions do not address the change in which way the ATF flows through the radiator transmission cooler for 2003 and newer TJs so the following modification to where its hoses connect should be followed:

For 2003 and newer models which use the 4-speed 42RLE transmission, the Derale cooler lines connect to the driver's-side transmission output port and the hard line the OE driver's-side hose used to connect to. Entirely remove the OE short hose that connected the driver's-side transmission cooler port to the hard line, connect the new Derale hoses to those fittings.

The Derale kit does not otherwise need any additional parts or modifications other than the supply hose leading to the Derale (the plain hose) now has perhaps 6" of extra available length. I left the additional length in place and located the small amount of extra length above the t-case skidplate. Those extra inches of available hose for 2003 and newer TJs may come in handy years down the road.

I expect Derale to add a section to their instructions to cover the 2003 and newer TJ whose transmission cooler flows the ATF through the OE transmission cooler in the opposite direction of the 2002 and older TJ.

The below photo shows the 2003 and newer hose layout connected into the driver's side. For 2002 and older, connect the Derale into passenger side instead.

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The first hose from the Derale cooler connects to the radiator’s return line. Derale includes two stainless steel hose clamps to be used here and on the other line but I reused the factory constant-tension spring clamps.

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The other new hose, which is the return line, connects here after the old hose is removed.

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Derale provides a cool way of attaching the coolant lines to the frame rail which serves to keep them parallel and out of the way of damage. Also provided are zip-ties to secure the hoses and wiring the rest of the way to their destination. Take pain now to insure everything is well secured and out of the way of potential harm.

The two (+ and -) electrical connections are made now.

The negative ground wire, remember, is the blue wire coming from the fan. NOT the black wire which for us electrical types keeps you on your feet. Connect the fan’s blue ground wire to a suitable ground connection. I simply drilled a 9/64” hole in the floor pan above the cooler for the supplied hex-head self-tapping ground screw.

To assure a good solid ground connection, be sure to grind any paint away from what you choose to ground the fan to as shown below. A Dremel tool makes quick work of this.

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Sorry about the fuzzy photo, it’s just to show to take care in how the wiring is routed.

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I connected the cooler’s +12v lead to an auxiliary fuse panel I installed last year.

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The last thing to be done is to add a quart of Valvoline ATF+4. This is needed due to the added capacity of the new Derale transmission cooler.

Don’t do what I did and pour the ATF in faster than the transmission fill tube can accommodate it! Within a minute or two, I had ATF dripping all over the floor and it scared the crap out of me. I had been careful about all the hose connections so it was a scary few minutes until I discovered the ATF had simply overflowed the fill tube. Add the quart of ATF+4 slowly and this won’t happen to you.

Voila, it’s ready for the test! I simply temporary bridged the connection at the thermostat switch and the fan came to life with a definitely audible satisfying roar. You’ll be able to hear it come on if you’re doing low-speed trail work, maybe not on the highway towing your trailer.

Start the engine, let it warm up and check for leaks. I put my hand on the new cooler once it was good and warmed up and it was definitely hot… but not up to 180 degrees because the fan was still off. It took some driving to warm it up enough that the fan came on. Good to go!

This is the final product. Even though I know from past experience that particular location is quite safe, I’m a bit anal about over-protecting everything underneath so I added a protective barrier since this Jeep wheels on a lot of big rocks.

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So in summary, the benefits of installing this transmission kit are...
  • Longer transmission life
  • Reduces the transmission’s ATF temperature by a very significant 30 to 40 degrees
  • Easily installed, completely bolt-in with no special skills needed
  • Thermostatically controlled 500 CFM fan
  • Peace of mind when towing, rock crawling, or just heavy traffic.
The quality of the stacked plate cooler itself is outstanding. This is not the cheap type of cooler that NAPA pushes for everything that is easily damaged by even flying insects. Its design is truly heavy-duty without the cheap aluminum fins that get squished together which reduces cooler efficiency. It’s a first-class stacked plate cooler that you have to see to appreciate.

The fan is big and also obviously built to last in the elements of water, mud, and dirt that will inevitably be flipped up onto it. When the fan turns on, it really pulls the air through the plates with authority. 500 CFM (cubic feet/minute).

Last step in the installation... drive it for a week and then get back underneath and check for any leaks where the hoses connect to the cooler. I found one that was weeping a tiny bit, probably from when I had to temporarily disconnect it to reinstall the fittings after learning that I had the two o-rings installed incorrectly. Give the AN fittings a quick test for tightness and re-tighten as needed.

What would I change if this was my product? Basically not a thing, it’s truly a great kit as is. If I had to come up with one enhancement, it’d be slightly longer hoses to give a bit more leeway on hose routing. The hose lengths are technically “perfect” as they were designed but just a tad more length would allow more flexibility in hose routing.

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Thanks for this detailed write-up. I used it to get mine installed as well as add a temp sender in the line between the radiator and aux. cooler.

I have been looking everywhere to find the ideal airflow for this cooler and cannot find an answer. Which way should the air be flowing for ideal cooling?

Blue or red?

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Currently mine is flowing in the direction of the red arrow, but I wonder if Blue would be better since there is so little space between the cooler and tub for much cool airflow and I would imagine that the air below the fan would be cooler and have better circulation.

Thanks!
 
Thanks for this detailed write-up. I used it to get mine installed as well as add a temp sender in the line between the radiator and aux. cooler.

I have been looking everywhere to find the ideal airflow for this cooler and cannot find an answer. Which way should the air be flowing for ideal cooling?

Blue or red?

View attachment 344282

Currently mine is flowing in the direction of the red arrow, but I wonder if Blue would be better since there is so little space between the cooler and tub for much cool airflow and I would imagine that the air below the fan would be cooler and have better circulation.

Thanks!

To be most efficient you want to pull air through the cooler. So blue arrow.

You can change the direction of the fan by rewiring your fan backwards. So if you had the blue wire to positive and black to ground flip them around and the fan will spin the proper direction.
 
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To be most efficient you want to pull air through the cooler. So blue arrow.

You can change the direction of the fan by rewiring your fan backwards. So if you had the blue wire to positive and black to ground flip them around and the fan will spin the proper direction.

Thanks I will rewire the switch. What I do not understand is that I have the blue wire as the ground and the black wire to positive just like Jerry's write-up. I know by reversing these two wires the fan will spin the opposite direction. I just do not understand why my electric motor would be the opposite as the write-up. (Although the instructions from Derale did say to test the connections prior to installation to see which wire was which to achieve the desired fan direction which I did not do).
 
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Thanks I will rewire the switch. What I do not understand is that I have the blue wire as the ground and the black wire to positive just like Jerry's write-up. I know by reversing these two wires the fan will spin the opposite direction. I just do not understand why my electric motor would be the opposite as the write-up. (Although the instructions from Derale did say to test the connections prior to installation to see which wire was which to achieve the desired fan direction which I did not do).

I had to do mine backwards from Jerry's write-up as well. it seems that at some point Derale made change to their wiring.
 
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First thanks to everyone for sharing their experiences, and I have a 99 with a 32RH transmission here in Dubai, UAE where 99% of my off-roading is small but technical sand dunes with lots of peak crests which causes lots of sand to come in contact with the underside of the Mistress (our teenagers named her that for obvious reasons much to my wife's amusement). The sand varies from hard packed faded orange to soft fine white like powder - my questions are:
  • has anyone else installed this automatic transmission in similar sandy terrain and what was their experiences?
  • As I have a reoccurring Automatic Shutdown from failing Crank Position Sensors (which overheat and shutdown), believed to be caused by overheating the automatic transmission either by excessive heat form the sun (50 degrees Celsius / 122 F) with radiant heat upwards from the sand as well as being rather energetic some days crossing the sand dunes, has anyone seen a change in vehicle performance with the installation of this under vehicle cooler?
    • Like many other over here, a transmission cooler mounted in front of the radiator has been tried but i don't like the idea of disrupting airflow to the radiator and the AC condenser.
    • Why did I have failing crank position sensors (long story short - don't buy cheap - buy Mopar!)
 
I don't wheel in sand much but it seems wiring the fan's polarity so the fan blows downward could help keep a lot of the sand out of the radiator fins. The few times I have wheeled in deep sand didn't seem to affect it.
 
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I just finished installing this unit.
Couple of things. If I follow instructions, then the airflow will be pulled up by the fan. This is how it is currently in my setup.
In my TJ Sport 2004, the spot where the bracket is supposed to be on a frame, is occupied by the arm that holds the step. So I had to sand off some piece of the arm.
The hoses are little short. Not more than 10 inches. Had to add some other hoses in the middle.
The fan is noisy, and you will definitely hear it when it runs.
I think that the biggest advantage is that no matter what the transmission temperature will be limited to 180F. In the summer, TJ coolant can easily reach 220 when idling with AC ( in my case even slightly higher, as I have autozone radiator).
It will help to cool the radiator as well - if the transmission oil temp is around 180F, then the radiator transmission area will server as a cooler to the engine coolant, taking away some heat from the coolant and dissipating if in the back.
 
I just finished installing this unit.
Couple of things. If I follow instructions, then the airflow will be pulled up by the fan. This is how it is currently in my setup.
In my TJ Sport 2004, the spot where the bracket is supposed to be on a frame, is occupied by the arm that holds the step. So I had to sand off some piece of the arm.
The hoses are little short. Not more than 10 inches. Had to add some other hoses in the middle.
The fan is noisy, and you will definitely hear it when it runs.
I think that the biggest advantage is that no matter what the transmission temperature will be limited to 180F. In the summer, TJ coolant can easily reach 220 when idling with AC ( in my case even slightly higher, as I have autozone radiator).
It will help to cool the radiator as well - if the transmission oil temp is around 180F, then the radiator transmission area will server as a cooler to the engine coolant, taking away some heat from the coolant and dissipating if in the back.

What's the temperature sensor in the trans oil pan show before and after, without guessing?
 
What's the temperature sensor in the trans oil pan show before and after, without guessing?

Didn’t install it yet, so don’t now.
However, on my first ping test ride, the fan kicked in, which means that it reached 180F, worked tor couple of minutes and then went off. It seems like it is not the highway 75MPH that heats the transmission, but rather the 40MPH in town, where most of the time torque converter is not locked.
 
Didn’t install it yet, so don’t now.
However, on my first ping test ride, the fan kicked in, which means that it reached 180F, worked tor couple of minutes and then went off. It seems like it is not the highway 75MPH that heats the transmission, but rather the 40MPH in town, where most of the time torque converter is not locked.

Once warmed up, my previous transmission only over heated at slower speeds (from crawling to about 20 mph and that was with a cheap cooler in the grill).

I boiled $200 worth of brand new +4 fluid one night playing in the rocks. That’s how I confirmed I had an issue before I had a temp gauge. Popped a fault light and then heard gurgling coming from my transmission when I inspected the engine bay and then transmission (I was not expecting that since most articles say the transmission will fail before transmission fluid boils at about 600*).

I was near the end of the trail and the temps dropped as soon as I got some air flow. I had zero water in the fluid and the mopar filter was new. I believe the transmission bypass valve (iirc) just had the transmission internally circulating.

I ordered a remanufactured transmission and drove using the scorched fluid until it arrived bc I didn’t want to lose friction material. At first I drove it around the block then a short trip…next thing I know I was driving it as a normal DD until the replacement showed up (I became very aware of the temps after installing the temp sensor). Couldn’t believe the transmission kept working as well as it did in Tucson from May to July.

I respect the 42RLE much more after putting mine through that and it not leaving me stranded. The hottest temp I recall seeing with the new transmission was between 160* and 180* and that was right before before Blaine installed a nice Setrab in conjunction with his steering cooler. Should be good to go now, but I’d likely install the version Jerry provided if I ever have issues.
 
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Once warmed up, my previous transmission (with a cheap grill cooler) only over heated at slower speeds (from crawling to about 20 mph). Boiled brand new +4 fluid one night playing in the rocks. That’s how I confirmed I had an issue before I had a temp gauge. Popped a fault light and then heard gurgling coming from my transmission when I inspected the engine bay and then transmission (I was not expecting that since most articles say the transmission will fail before transmission fluid boils at about 600*).

I was near the end of the trail and the temps dropped as soon as I got some air flow. I had zero water in the fluid and the mopar filter was new. I believe the transmission bypass valve (iirc) just had the transmission internally circulating.

I ordered a remanufactured transmission and drove using the scorched fluid until it arrived bc I didn’t want to lose friction material. At first I drove it around the block then a short trip…next thing I know I was driving it as a normal DD until the replacement showed up (I became very aware of the temps and made sure to not let it get too hot during those two months). Couldn’t believe the transmission kept working as well as it did in Tucson from May to July.

I respect the 42RLE much more after putting mine through that and it not leaving me stranded. The hottest temp I recall seeing with the new transmission was between 160* and 180* and that was right before before Blaine installed a nice Setrab in conjunction with his steering cooler. Should be good to go now, but I’ll install the version Jerry provided if I ever have issues.


The whole point of this Derale cooler is that it has its own thermal switch and fan, and pretty much guarantees that no matter what happens transmission temperature will never get beyond 180F. Based on my experience driving last days, it is a slow stop and go traffic that brings the transmission temperature to be hot. A cooler without its own independent fan will not be really effective in slow traffic. Such a cooler is better than nothing, but not a real solution.
The fan on this unit is very strong, it is like 7 inch fan.
 
The whole point of this Derale cooler is that it has its own thermal switch and fan, and pretty much guarantees that no matter what happens transmission temperature will never get beyond 180F. Based on my experience driving last days, it is a slow stop and go traffic that brings the transmission temperature to be hot. A cooler without its own independent fan will not be really effective in slow traffic. Such a cooler is better than nothing, but not a real solution.
The fan on this unit is very strong, it is like 7 inch fan.

I’m not knocking your cooler choice. I was relating that I’ve also experienced seeing a warmed up transmission get hot at lower speeds.

However, be careful about knocking a cooler simply because it doesn’t have a electric fan. There is much more to the equation.

Look again at the design and surface area of the Setrab at tell me which one looks like the better cooling device. There’s a lot of cooling taking place as the oil makes its way through the passages at speed or when the mechanical fan is on. It cools far better than smaller cheap coolers up front because the design is superior and surface area and internal volume is much larger.

Edit: I have to disagree with your statement. Not only is it a real solution it’s arguably superior bc it cools without risk of an electric fan not kicking on since the mechanical puller fan is sucking air though a large amount of surface area. This is not to be confused with a cheap little cooler.

That said, based on what’s available I would 100% have the same cooler as you if the one I chose didn’t exist. All is good.
 
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To me, that location looks pretty exposed to damage if you wheel the rig. Have you given that any thought?

I ran that cooler for a few years, and it does work well - aside from the noise. But on my rig I tucked up against the bed and built a guard to protect it. Since I run an LJ I had some extra room there to do so.

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I’ve since changed to a larger cooler in front of the radiator, which I do like much better.

Edit: By the way, I still have this cooler, guard and all. If anyone is thinking about installing one of these things, let me know and it’s yours.
 
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To me, that location looks pretty exposed to damage if you wheel the rig. Have you given that any thought?

I ran that cooler for a few years, and it does work well - aside from the noise. But on my rig I tucked up against the bed and built a guard to protect it. Since I run an LJ I had some extra room there to do so.

View attachment 373323

I’ve since changed to a larger cooler in front of the radiator, which I do like much better.

Edit: By the way, I still have this cooler, guard and all. If anyone is thinking about installing one of these things, let me know and it’s yours.

I don’t do any serious rock crawling. Forest roads, national parks, scenery, nothing too technical. As a result
If I would, then I would have much higher lift (I have maybe 1.5 inch) and would have enough space above the axle and would put it there (same place as you put).
The guard on the bottom similar to what you have I thing is a must, because otherwise anything getting to it (even a piece of wood) would cause a damage. I will make one myself.
With the radiators in the front of the grill - my concern (and maybe it is just my mistake) is that it will get the transmission too cold. What I am reading, the transmission needs to be at 175F. Not colder, not hotter. This is why on a lot of vehicles you see heat exchangers that have sole purpose of heating up the transmission fluid. Radiator in front will keep the transmission colder than it should be, because the airflow is not thermostatically controlled.
 
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I’m not knocking your cooler choice. I was relating that I’ve also experienced seeing a warmed up transmission get hot at lower speeds.

However, be careful about knocking a cooler simply because it doesn’t have a electric fan. There is much more to the equation.

Look again at the design and surface area of the Setrab at tell me which one looks like the better cooling device. There’s a lot of cooling taking place as the oil makes its way through the passages at speed or when the mechanical fan is on. It cools far better than smaller cheap coolers up front because the design is superior and surface area and internal volume is much larger.

Edit: I have to disagree with your statement. Not only is it a real solution it’s arguably superior bc it cools without risk of an electric fan not kicking on since the mechanical puller fan is sucking air though a large amount of surface area. This is not to be confused with a cheap little cooler.

That said, based on what’s available I would 100% have the same cooler as you if the one I chose didn’t exist. All is good.

Mechanical fan superior to electric, for sure.. stronger, more reliable etc. The problem with the mechanical fan in this case that is it thermostatically controlled, just not by the transmission temperature, but by the radiator temperature. As a result most likely you will get much more cooling that you need to your transmission. My understanding that it is designed to be at ~175F, exactly as the engine is designed to be at around 200F/210F. I might be wrong but the only way to get to transmission temperature of 175F (not lower) is to eliminate airflow if the transmission is below the operating temperature, and thermally couple it with engine coolant for preheat purposes (engine gets to 210F really fast compared to transmission).
 
To me, that location looks pretty exposed to damage if you wheel the rig. Have you given that any thought?

I ran that cooler for a few years, and it does work well - aside from the noise. But on my rig I tucked up against the bed and built a guard to protect it. Since I run an LJ I had some extra room there to do so.

View attachment 373323

I’ve since changed to a larger cooler in front of the radiator, which I do like much better.

Edit: By the way, I still have this cooler, guard and all. If anyone is thinking about installing one of these things, let me know and it’s yours.

Jerry’s done a sizable amount of rock crawling and never reported having any problems.
 
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Mechanical fan superior to electric, for sure.. stronger, more reliable etc. The problem with the mechanical fan in this case that is it thermostatically controlled, just not by the transmission temperature, but by the radiator temperature. As a result most likely you will get much more cooling that you need to your transmission. My understanding that it is designed to be at ~175F, exactly as the engine is designed to be at around 200F/210F. I might be wrong but the only way to get to transmission temperature of 175F (not lower) is to eliminate airflow if the transmission is below the operating temperature, and thermally couple it with engine coolant for preheat purposes (engine gets to 210F really fast compared to transmission).

The trans fluid runs through the radiator, which heats/cools it towards proper operating temp. Over cooling isn’t a problem when the aux cooler is sized properly especially when the transmissions wants to heat up more under load at lower speeds when the fan would kick on and when the water pump is turning less at idle.
 
Jerry’s done a sizable amount of rock crawling and never reported having any problems.

If memory serves, Jerry mounted his up behind the skid plate which protected it a bit more (if he sees this, he can clarify). Texas TJ's is in a much more exposed location.

But as he said, it makes a difference where you wheel. Here in TN, a tree branch would find that thing in a heartbeat,
 
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