Installing an Automatic Transmission Fluid Cooler

Discussion in 'How-to Guides' started by Crawdaddy, Jul 9, 2008.

  1. Crawdaddy

    Crawdaddy Moderator

    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 ½ 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.
  2. Dan

    Dan New Member

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

  3. Crawdaddy

    Crawdaddy Moderator

    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. collinsperformance

    collinsperformance New Member

    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
  5. tbplus10

    tbplus10 Super Moderator

    Great tech article Christopher.
  6. Crawdaddy

    Crawdaddy Moderator

    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. :(
  7. FordAssasin

    FordAssasin New Member

    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:great::great::great:
  8. Jimmiee

    Jimmiee New Member

    Good write up Chris and nice pictures however you will hate me after you read what I have to say. :)
    I have to take issue with running rubber cooler lines all the way from the transmission to the cooler. This is a no no and not recommended. I have seen this done before and they just do not hold up to the elements. The rubber lines will get hard over a year or two and crack. Also they tend to rub through wherever they touch metal
    Also those cheesy nylon ties that are installed through the fins should never be used! They will ruin your radiator and will cause leaks after they have been there for about a year. I have seen too many radiator leaks over the years because of these ties. The good aftermarket coolers come with metal straps which mount the cooler securely to the truck without touching the radiator. You can buy these separately as a kit from TruCool. TruCool makes the best aftermarket coolers IMO and are OE in many applications as an auxiliary cooler. They are a stacked plate design rather than a fin and tube style. They have a much higher cooling capacity as well.
    As you say there are pro's and cons about bypassing the radiator. If you live in a cold climate do not bypass the radiator! The ATF needs to get warmed up by the radiator in order to flow and this is your lube oil. New trucks nowdays have a built in bypass system so fluid will flow in cold climates because sometimes the radiator is not enough until it gets hot and this can take a while in sub zero weather.
    Keep in mind the stock radiator is designed to cool the transmission and the heat it makes as well as warm it up quickly.
    Another downfall of bypassing is a stand alone cooler needs airflow. They work great on the highway but not around town or off road where the going is slow.
    Last but not least is the GVW rating you see on the cooler box. Most people don't know that this rating is compiled with the stock radiator cooler in series. If you bypass the radiator then cut that rating in half! You may think you have enough cooler but in fact you do not.

  9. Crawdaddy

    Crawdaddy Moderator

    Well Jimmiee, I don't hate you, but that's some not-so-good news. As for the rubber lines all the way back, I did it because I didn't want to risk having a line leak at a juncture between rubber and steel line. So far the lines seem to still be pretty soft and pliable, and it's been at least a year since I put the cooler in. I would like to upgrade the cooler and possibly add in a second cooler because I plan to tow with the truck and I do plan to idle the truck a decent amount. I don't think I'll have any lack of heat issues, it's a bit hot down here... :lol:
  10. Crawdaddy

    Crawdaddy Moderator

    So, I'm working on completely rebuilding my automatic transmission cooler setup. There's a couple of reasons behind my descision. First, with the setup I did before, I am not confident that I can pull my 9000 pound camper without overheating. The cooler I selected was probably just barely adequate to cool the transmission by itself in the configuration I had it in. Second, I wasn't taking advantage of the cooling and pre-heating offered by running the ATF first through the engine radiator. Third, I apparently had the cooler oriented in a position in which air pockets can get trapped in the cooler, reducing cooler performance. Granted, this cooler has not given me any issues in the 3 years I've had it installed, but I haven't really towed heavy loads that often during that time either. So, time for an upgrade.

    There are some things I'm going to keep the same with the upgrade, like the ATF cooler hose. Jimmiee advised against running the rubber ATF cooler hose the whole way up, but I haven't had any issues with it, so I'm going to keep running them. I also had left the original steel cooler lines in the truck in case I had to go back to them for any reason. I've now cut out 98% of them leaving only about 4" stubs that hook up to the radiator to give me something to splice into. So, fluid is going to be routed from the transmission, into the external ATF filter, past the temp sender, into the bottom port of the engine radiator, out the top port, into the bottom port of the B&M cooler, out the top, and back to the transmission.

    The cooler I chose to go with is the B&M Universal SuperCooler part number 70274. This is a universal cooler that's good for oil, ATF, power steering, and most other low to mid pressure applications. It's capable of dissapating 29,200 BTU of heat. It measures right at 11"x11"x1.5" for the core, plus another 1/2" or so for the mounting fins. It has 1/2" NPT fittings for ease of hooking it up. Here's a picture of it sitting next to my new AutoMeter transmission temp gauge (more on that later):

    I figured while I was rebuilding the cooling system, I might as well add in some additional filtration to get all the little particles of clutch out. So, I went back to B&M and picked up their remote transmission oil filter kit, part number 80277. It has 1/2" NPT ports on top and accepts a PH8/TG8 filter. I would have been happier if it were a TG5 filter so it would be the same as the engine, but I should have the TG8 filters on hand for my Bronco's engine.

    I also picked up an AutoMeter Z-Series transmission temp gauge. I'm planning on putting the temp sender in the transmission pan when I get a pan with a sender port in it, but for now it's going inline with the cooler.

    So, I got all the parts in, and started looking over the front of my truck to determine how I wanted to mount it. I was originally going to mount it with the ports pointing down like my old was, but B&M strongly discourages that, so I had to rethink my plans. I was able to come up with a mounting solution that allowed me to put the cooler horizontal, but then I was having clearance issues with the horn. I figured out by putting the cooler very low, to where a little bit of it's behind the bumper, that I could fit the cooler in. I put a 90 degree fitting on the top port to make hose routing easier. I used a pair of 2" wide pieces of flat aluminum to make the cooler wide enough to screw into the radiator core support. I used self-tapping screws to make installation easier. So, here's what I ended up with for the install of the cooler:



    The brass 90 degree fitting will be painted flat black to match everything else. I probably should have done that before putting the cooler on the truck, but oh well. I haven't checked clearance yet with the grill, but the cooler is far shallower than the center core support brace, so it should fit with no problem.

    With that out of the way, I turned my attention to assembling the transmission external filter setup. First I had to determine where I wanted to mount the filter. Obviously I wanted the filter to be easy to get to and not make a mess during filter changes, but it also couldn't be the lowest part on the truck where it could get sheared off or otherwise messed up. I decided to put it on its side up on the framerail on the passenger side right where the transmission cooler lines passed by. I used a piece of 1.5" angle aluminum to make a bracket to mount to the lower framerail with. I then installed a 1/2 NPT to 3/8 hose barb fitting on the IN side of the filter, and a T-fitting and another 1/2 NPT to 3/8 hose barb fitting on the out. In the T, I installed the temperature sender for the transmission temp gauge. I know it's not the best place to get an accurate picture of the transmission temperature, but it will give me relative readings until I can install it in the pan. Here's some pictures of the filter assembly aseembled:




    It looks big and ungainly, but it would have been much cleaner if the temp sender hadn't been there.

    So, now I still need to mount the filter, buy some 3/8" ATF cooler hose and extra ATF fluid, and assemble the system. I'll probably buy the parts this week and finish the assembly and install on Saturday.
  11. Crawdaddy

    Crawdaddy Moderator

    One more thing I've noted is I may need to put a jumper wire between a bolt holding the filter onto the angle aluminum and the frame. The temp sender needs a good electrical ground, and I may have broken that ground path by painting the bracket. We'll see how that one goes.
  12. Crawdaddy

    Crawdaddy Moderator

    I mostly finished the install, but was 2 hose clamps short. So, it's put off until I can pick up some more hose clamps, hopefully tommorow evening.

    In light of unplanned new funds, I reworked the transmission filter housing fittings to remove the T-fitting and temperature sender. The sender will be installed in a deep transmission pan. So, the filter housing now only has 2 1/2" NPT to 3/8" barb fittings. I installed the filter housing on the passenger frame rail silghtly behind the cooler fittings on the transmission to simplify hose routing. Unfortuately, I could not put the bracket on the top part of the frame rail, but there was a clearance issue with the fuel lines, so I put it below. Here's a picture of the filter housing installed:


    I also ran the rest of the hoses, and here's a pic of what the cooler area looks like with the hoses installed and the hose routing under the front bumper:


  13. Crawdaddy

    Crawdaddy Moderator

    Well, yesterday I put the finishing touches on the cooler setup. Put the 2 final hoses on, and started warming up the truck looking for leaks. So far, the only leak I've found is the actual transmission filter I installed, and it's just a tiny seep. I suspect I overtightened it and it's leaking, either that or it's not tight enough. Next weekend I should be swapping out the transmisssion pan and doing a fluid swap, so I'll take care of that leak then. I'll also get some pics of the final install and my hose routing. I'd say it looks pretty good, and I hope it sure cools well.
  14. rshepard

    rshepard New Member

    Great tech article
  15. Crawdaddy

    Crawdaddy Moderator

    I somewhat test fit the grill on a couple days ago, and I may have a slight clearance issue with the hoses at the B&M cooler. I didn't fully install it because it's a pain with the bent up front bumper, but I'll sort out the clearance issues.
  16. Conlan Rose

    Conlan Rose Super Moderator

    Did you use regular house hold brass pipes for the sender unit T? I plan to do a set up similar to yours in the near future, but I plant to use two 13,000 BTU B&M coolers that are very slim and allow me to install cooling fans over them.

    I will be using the same Autometer gauge and remote filter. I just am wondering what fittings I may need. I know that my tranny is different than yours (4L60e), but there must be some parallels.
  17. Crawdaddy

    Crawdaddy Moderator

    I did use regular brass fittings. I heard that they may not take the heat cycles very well, but I've had pretty good luck so far. The fittings in the transmission case are pipe thread to hose barb fittings. I don't remember the diameters, but the dimensions between the 700R4 in my transmission and the 4L60E should be the same as it's the same transmission, just electronically controller. I also used rubber hose and hose clamps to make up all the lines. However, that's probably going to change in the near future. I think I am going to switch out the lines for the stainless braided lines and AN fittings that are commonly used in the racing and off-road world.

    Yesterday I towed my camper for the first time with the suburban. The 700R4 did fine with all my mods with the exception of a hose clamp on the out side of the transmission cooler line at the transmission case was loose and dripping ATF at a decent rate. The transmission stayed no higher than 150 degrees, but the ambient temp was in the 40s and I could only tow at 45-50mph due to sway.

    Cooling the transmission with those 2 coolers in tandem with the stock cooler should provide plenty of cooling for most operations. The one thing I don't like with your plan is the addition of another 2 fittings that could potentially leak. The Automater gauge is quite nice and quite attractive in my opinion. I put the temp sender in the temp sender bung of my deep transmission pan even though I was originally planning on putting it in that T fitting at the external transmission filter. The one thing I have to advise if you go the T-fitting route is to not put the T higher than the rest of the line even though that makes more sense to keep it high and out of the way. Putting it higher could make it sit in an air pocket and not read correctly.
  18. Conlan Rose

    Conlan Rose Super Moderator

    I am most likely going to not go through the radiator cooler. If you think about it running ATF through the cooler isn't really cooling it if the engine is running at normal operating temp, 195+, it is already heating you fluid not truly cooling it. and same vice versa if the tranny is running hot it will warm up your coolant which you are trying to cool down.

    I plan on getting a B&M deep pan so I may put the sender there is it fits if not I will mount it on the out line on the tranny. I just remembered I have a blog entry on what my plan id with all info and links to products.

    I most definitely will have many questions about how to do this because I'm replacing the whole tranny cooler system. My current lines are rusty and need to be replaced.
  19. Crawdaddy

    Crawdaddy Moderator

    2 things to think about when making the decision to not run the ATF through the radiator. First, the ratings for the auxiliary coolers are based on the fact that you are adding the cooler to the loop, not replacing the existing cooler in the radiator with the aux cooler. Second, having heat exchange between the antifreeze from the motor and the ATF in the transmission is actually beneficial to the operation of the transmission. If the fluid is too cool, the transmission will not perform at optimum ability and damage could occur. That said, I am running through both the radiator cooler and my aux cooler to try to keep everything optimum.
  20. Conlan Rose

    Conlan Rose Super Moderator

    Ok, so I should still use the factory radiator cooler. I will still replace the line to the cooler because it is rigid and rusted to heck. Should I keep the factory engine oil cooler routed to the radiator?

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