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  1. #1

    Default Installing an Automatic Transmission Fluid Cooler

    Installing an auxiliary transmission cooler is really not that difficult once you do a little research, but it is VERY messy. I want to say that the total time it took my uncle, cousin and I to install the cooler on my Suburban was probably about 2 hours from start to finish, but this was also working at a casual pace with reasonable breaks.

    A few things have to be investigated before starting on this project. First is determining whether you want to put this cooler in-line with the existing factory cooler or in replacement of it. I decided to replace the factory cooler with mine. This can have a couple advantages and disadvantages. You allow the radiator to cool more efficiently by not injecting 200F+ ATF fluid into the same space you are trying to cool antifreeze with. However, if you choose and undersized cooler, you may cook the transmission. So, using the factory one in conjunction helps ensure that you have adequate cooling ability. The second to check is the fitting size and threading on the case of the transmission. For the TH-700R4s found in most ton trucks until 1988 (I think) for pickup trucks and up to 1991 in Suburbans, the transmission cooler fittings on the transmission case are 1/4” pipe thread fittings. For other transmissions, it appears this page ( has a lot, if not most of the fitting sizes and threading. Now, let’s go through a brief parts list…

    Parts Needed: You could also buy these from a gm dealer such as
    Transmission Cooler (Link) Autozone part# 911516 (I’m pretty sure this is the one I used)
    2x Pipe fittings (1/4” pipe to 3/8” MIP)
    Automatic Transmission Cooler Line (watch out, this stuff if like $1.25 a foot)
    Teflon tape
    Hose clamps to fit the ATF line
    Quart or two of the appropriate ATF fluid for your truck

    OK, get the truck in a fairly comfortable spot and let it sit there for a good long while. When a transmission is at operating temperature, ATF fluid can run in excess of 200F in the transmission. During this time, you can be planning your method of attack. Also while the truck is cooling, start disassembling the front grill, you have to get all the way down to the radiator, so it’s gonna be a pain to get all that trim and grill off. Now you can start on disassembling the existing transmission cooling system. For my truck, the factory cooler had steel hard lines that ran from the transmission to the radiator. I left them in place and connected to the radiator in case I had issues with the aftermarket cooling, but I plan on removing them later on. Make sure you have a drain pan handy on whichever side or sides you remove the cooler line at. Now you can mount the transmission cooler to the front of the radiator. Make sure you don’t have to make any sharp bends or sharp edges with the cooler line and that you can get to the fittings. I faced my radiator on its side with the fittings facing the bottom so that I could go down and straight under the truck with the lines. I put it on the passenger side since that’s the side that the cooler fittings are on the transmission. It uses this weird tie-wrap that’s designed to go through a radiator to secure things. As such, it’s one-time use only, so make sure you get it right before you go putting the 2 halves of the tie-wrap together. Now, you need to route the cooler lines back to the transmission. I was able to route mine along the fame rail under the motor mount bracket up to the point where the cooler lines go into the transmission. I had a little extra line that I didn’t feel like trimming off, so I then followed my fuel lines heading out into the open to cross the gap and take up the slack. Put a few turns of Teflon tape on the threaded side of the fittings and crank them into the case until you bottom out the fitting. Slip the cooler lines onto the fittings and tighten them down with hose clamps. Crank the truck up and cycle the gears to get the transmission fluid flowing. CAREFULLY feel the radiator to see if it’s getting warm. Inspect for leaks and check the transmission fluid. Chances are you lost some fluid from the work and having to fill the new cooler and lines with fluid. Add fluid as needed to get you back up to the proper level. Put the grill back on and admire your work.

    I wish I had bought a remote filter and a transmission oil temperature gauge before I did the install, but everything’s easy enough to get to that it should be easy to add those in. I even have enough spare line to complete the connections. I have yet to tow anything with the truck yet, but I can only assume that the cooler is doing its job well. However, time will tell as I have no way of telling for sure now whether the transmission fluid temps are lower or not. I used standard brass plumbing fittings in the transmission case. From what I understand, brass doesn't like very high temperatures, but I think it should be ok... The temperature of the oil shouldn't get so high that it causes the brass to fatigue. As usual, I didn’t take any pictures while doing the work, but I’ll try to get ya’ll some pics soon of all the connections and such. If you have any questions, feel free to ask me and I’ll do my best to answer them.

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 277K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half

    There are 10 kinds of people, those who understand binary, and those who dont...

    Remember kids, the only difference between screwing around and science is writing it down- Adam Savage

  2. #2


    on my 2006 sierra i bought the kit from gm all hoses complete took 30 start to finish


    2006 GMC 1500 Long Bed Vortec 4.3
    1982 S-10 Prodject Street/Track with a 327/300hp Motor built up to 415 hp

  3. #3


    as promised, here's some pictures of the end result

    how the radiator looks behind the grill

    routing of the lines down from the cooler to under the truck

    routing of the lines when they get to the transmission case

    I didn't get any good pics of the brass fittings, or of the routing through the engine mount. I was taking these while trying to not get on the ground. The suburban sits in some dirt when I'm not driving it... I'll try to get some shots of that stuff tommorow when I'm inspecting the system after driving it.

  4. #4


    just a tip put a rubber firewall plug around the wires going thru the drip pan. the wires will vibrate and move and chafee this will be a short some time soon and be a bad thing. you can take some vaccum hose split it then wrap the wires and put 1"of hose on both sides of the metal and tape or zip tie it off......just a tip otherwisw this is great........thanks....mike
    Michael Collins
    1993 4X4 Suburban
    many other toys as well

  5. #5


    Quote Originally Posted by collinsperformance View Post
    just a tip put a rubber firewall plug around the wires going thru the drip pan. the wires will vibrate and move and chafee this will be a short some time soon and be a bad thing. you can take some vaccum hose split it then wrap the wires and put 1"of hose on both sides of the metal and tape or zip tie it off......just a tip otherwisw this is great........thanks....mike
    Never thought about that, but that's not a bad idea. Those are just ground wires, but I imagine that it would suck to go turn the lights on and not have them.

    Oh, and on the second picture, it's important to note the chunks of cooler that I cut in half and tie-wrapped to the real cooler line. This is to protect the cooler line from getting chafed or cut by the radiator core support.

    Oh, and on a side note, I'm not sure where it's going, but it looks like I'm STILL losing ATF somewhere... I have to get under the truck with some brake cleaner to clean the transmission area of the truck so I can figure out where it's coming from. :(

  6. #6


    Love It!! My buddy did the same thing on his dodge van i know dodge uuugghhh haha but im curious on this mod working for my 99' Tahoe,I have a trans temp gauge on order but i would like to add the aux cooler for the tranny and give my radiator a break. So let me know if this will work on my Tahoe she has the 5.7L Vortec and its 2wd and again great write up

  7. #7


    Great tech article Christopher.

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