I do a lot of towing. A lot of really heavy towing. Campers and horse trailers with either horses or full of hay. Sometimes these trailers weigh over 7000 lbs and on occasion have no trailer brakes. Because of this, my transmission takes a beating and I've noticed it gets a little warm on occasion, though never enough to set off the warning. That said, a cool transmission is a happy transmission and I would like to not have to replace mine before I'm totally ready to do so, and I already had another factory transmission cooler from my parts truck to use, so I decided to install it as a second trans cooler instead of an oil cooler since my engine stays cool enough for my liking already. You can see my other write ups for my cooling system mods, and there is one more coming with a modified version of the inline thermostat mod.

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So here we go. The parts you'll need:

Factory transmission OR oil cooler - ~$45 on eBay, but check with Abran or Paul Grant

1/2" High Pressure Hose, I used this - $22

1/2" Hose Y, it's important that these can withstand enough heat. I used these - $11

A quart of ATF.

And some band style hose clamps. You'll need eight.

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And here's the write up. If you have the factory mechanical fan, you might have to remove the shroud. I'm honestly not sure. I left my electric fan in place.

I started by removing my intake. You can probably work around it, but mine was in my way.



It appears I didn't picture this next part. Sorry about that. You'll need to remove the bolts holding the radiator to the mounts that hold both the radiator and the transmission cooler in place. The top has a bolt and the bottom just slips in by sliding front to back. Don't try to pry it away from the radiator because you might mess up the bottom sliding mounts, slide them apart. You may have to use a screwdriver or something to pry. Your radiator should lean back relatively easily now.

Now that that's done, you'll have to CAREFULLY cut the hose shield over the drivers side hose. Do try not to cut the hose itself.



Now take two pairs of vice grips. I'm still on the drivers side here. Ignore the horn, I moved mine and yours will not be there. Clamp the hose as close to each end as you can with plenty of space in between.



I really didn't take as many pictures as I usually do for this write up. I apologize. Next you'll want to cut the trans cooler hose around the middle of the length you have clamped off. Some ATF may pour out. Slide your hose clamps on either end and then slide your hose splitter into each end and clamp it down like so.



On the passengers side of the cooler, I recommend putting the hose on before installing the cooler, but it can be done after you've installed the cooler. I did, but I'm not totally happy with how tight I got it.

You're still on the drivers side. You need to actually install the cooler now. From the factory you've already got a spot for it to mount. One end slips in and the other end has a bolt. Then you'll need to install the line which will run from the hose y to the drivers side of the cooler. It will likely be a little hard to slip onto the cooler. Take some oil or ATF to lubricate the cooler inlet as well as the inside of the hose to slip over it so you can get it on farther, and then clamp it down nice and tight on both ends.



You may now remove your vice grips and move to the opposite side. Again, you'll want to clamp the hose several inches apart.



Do the same cut and splice as before with the hose y.



Now, if you decided to ignore my warning above, install the passengers side hose onto the cooler now. Same procedure as before, just a tighter space. I decided to add some ATF at this point. Using a funnel, SLOWLY start to pour some ATF directly into the cooler.



Now remove the funnel and keep your finger over the end of the hose. Make sure you've got your hose clamp already slipped onto the hose, and if you do go ahead and lower the hose down to slip it over the hose y. There's no clean way to do this, just do it as smoothly as possible. slide the hose off of your finger and directly over the hose y and then clamp it down.



Now go ahead and raise the front of your truck up to check the fluid level. I ended up adding just a little. If it hasn't been done in a while, you might as well go ahead and change your fluid and filter. If you don't have the correctly sized allen key to get the transmission filler plug out, a TX50 torx head will work. Same size as is used on the back seats, I believe.



I will also tell you, a kerosene pump is the easiest way to get transmission and differential fluid out of the bottle and where it needs to go.



I hope this helped some of you all out! If you have any questions or have any ideas as to how this mod or write up could be better, or anything else to say, post it below or feel free to PM me and I'll respond as quickly as possible. Also go down to the link in my signature and check out my other write ups!

 

Alex ... What type of cooler did you use? Can't really tell from the photos. An apologize my newbiness, but what kind of cooler is stock on those?


My RRC runs the tranny oil through the radiator oil ports, and then also runs it through a "bog brush" cooler located in front of the AC condenser. I was looking at swapping the bog brush for an aluminum oil cooler (radiator style) and wondering how much efficiency I'd gain.


I also see that you did an AC delete. Guessing that you removed the condenser as well? That'd be a big boost the engine cooling capacity... I'm also looking to improve tranny and engine cooling for towing with my RRC ... just trying to figure out what will give me the biggest bang for the buck....

 

Also... I noticed you also did the inline thermo mod. I'm not sold on this honestly, but please feel free to correct me. But this mod only helps reduce temps during normal operating temp conditions right? I am really looking at increasing the cooling capacity while at the edge of the cooling system capacity (thus when the thermostat is already in a condition where it is fully open). And that's why I don't believe the inline mod will do me much good. I also am not a huge fan of tricking the ECU (in air/fuel ratio and timing), which the inline mod seems like it does. Engineers spent a lot of time balancing the ECU software...

 

Alex, you should be able to tow up to 3500kgs (7716lbs) with a D2. I've covered 20K miles towing with a full 3.5 ton load up steep hills in France without overheating even during the summer months at 40C. However, having a secondary transmission oil cooler is by no means a bad move especially if you tow offroad and in mud as the mud often doubles the towed weight.

 

I used another trans cooler I had from my 04 parts truck. It's just another factory cooler.

You won't notice anything from doing an AC delete. I did remove the condenser, spent 45 minutes trying different length serpentine belts, etc. Just leave your AC turned off. Actually, the condenser is why I did the delete. I accidentally poked a hole in it with a self drilling screw...

I love the inline mod what little bit I've gotten to use it. I don't know exactly what you mean when you say it tricks the ECU. If it does it's not a part of the design. I've noticed cooler regular running temps and more regular temperatures across all conditions. The temperature gets up to running temp pretty quickly and then it just holds without fluctuating, unlike the factory setup from which I noticed a lot of swings.

 

The US manual reads 5500lb or 7700 in low range. I've always gone by the UK ratings, though. I've towed 7500lbs of trailer/hay bales behind it up and down hills, through pastures, etc, during 90 degree F weather. That specific instance I noticed the trans getting a little warmer (I could feel the heat coming up the bottom portion of the shifter) which is when I decided to the increased trans cooling capacity. Sadly, I haven't gotten to tow with it since, but once I'm out of college and have a job she'll go back on the road and be used a lot more regularly and I expect to see a major difference then.