Auto Transmission Cooler

About 8 months ago, I removed the AX-15 manual transmission and installed an AW-4 automatic transmission.  At the time, I opted to use two smaller fluid coolers instead of a larger model.  One, with a 400 CFM 12V fan, was mounted over the rear axle.  It was my “backup” cooler and the fan would energize when a preset temp was reached.  It was my plan that the fan powered cooler would kick in when I had higher than normal tranny temps on the trail or when rock crawling.  The primary cooler was to keep the temps under control during normal driving conditions.

Everything worked well until the Phoenix summer arrived.  While the tranny never overheated, I didn’t like the 195 temps it ran at in heavy city traffic.  The highway driving was OK but stop and go traffic would warm things up again.  I knew the problem….and I knew it when I “made” the problem.  It was the placement of my primary cooler.

Here is the B&M stacked plate aluminum cooler I used.  As I mentioned, it saw the fluid as it came out of the transmission.  The cooler was mounted on a bracket that was welded along the frame rail, adjacent to the transfer case.  During the installation, I used -6AN fittings so if I needed to move anything in the fluid line, it was easy enough to just unscrew it and move as necessary.

So move it did….to the front of the vehicle where the air flow through the cooler would be better.  I had originally avoided the grill area as I didn’t want to contribute to the radiator’s heat load.  My brief trip today (about 25 minutes) in a mix of freeway and city street driving showed promising results.  It was about 100 degrees outside (cloudy/cool day) and the engine’s temp gauge behaved itself.

I picked up some new synthetic tranny hose at local performance shop and stopped by AutoZone for a quart of ATF.  Four more -6AN fittings were purchased along with two union fittings.  I already had some 6061 aluminum flat stock to use for mounting the cooler in the grill area.

Troy (of Toys by Troy) let me have a lift for the day while I did worked on the project.  This would not normally be needed but since my center skid completely covered the cooler’s existing mounting spot, it made things really easy to put the TJ on the lift so the center skid could be removed.  With the center skid gone, I unbolted the cooler from the bracket.  Two -6AN fittings were pushed into the end of the hose and I connected both, using the two unions, to the existing synthetic hose.  I routed the new hose up along the frame rail and down to the steering box where I slipped it up into the grill area. 

You can get resonable access to the grill area by removing the driver’s side headlight.  Three screws hold the trim ring in place.  With these removed, you can remove the four T15 Torx screws that hold the headlight retainer ring in position.  Depending on the dimensions of your cooler, this is one way to get it behind the grill.

Here is the headlight mounting fixture after the headlight ring is removed and the headlight unplugged and removed from the fixture.  If you look on the back side of this mount, you will see that it is held in place by 3 small bolts.  The nuts can be removed from the back side.


With the nuts removed from the back side, the mounting fixture can be removed to provide more clearance for easier working conditions.


When Troy saw me measuring the aluminum flat stock I had brought to mount the cooler, he grabbed a universal mounting kit made by Flex-a-lite (the fan company).  The part number is 32125.  It was intended to mount fans and coolers and Troy had recently used one on another TJ tranny cooler install with good results.  Instead of flat stock, it is aluminum c-channel and comes with trick little mounting bolts that do not require a wrench to hold them in place while tightening the nut.  I cut off the excess c-channel and attached the cooler to the c-channel.  Love it….instant mounting brackets and I didn’t have to drill any holes in the aluminum either.

Auto Transmission Cooler

I borrowed a vehicle and ran down to the local ACE hardware store.  I picked up 4 button head 1/4″x20 allen screws along with 4 Nyloc nuts.  I also purchased 4 plastic spacers, about 1/2″ in diameter by 1″ long with a 1/4″ hole drilled through the length of the spacer.  The spacers will be used between the grill and the mounting brackets so that the grill metal does not collapse as the mounting screws are tightened.  I got some changed back from the $5 bill I gave the checkout person and headed back to the shop.

I roughed out the measurements for the hose and cut them to length.  I had bought about 6~8 extra feet of hose which I intend to keep in the trail spare box.  With a couple of -6AN fittings and a union, it will make for a good splice should the need arise.

I measured the distance between the two mounting brackets (about 4″ in my case) and then drilled the four 1/4″ holes in the grill.  The cooler was then slipped into position and the 1″ long spacers were put over the screws.  This allowed the mounting brackets to be snugged down tight without the chance of crushing the grill sheet metal.  The -6AN fittings were threaded onto the matching fittings on the cooler and then everything was tightened in place.  As I mentioned earlier, I used Nyloc nuts to prevent the mounting hardware from vibrating loose.

Had I not been running short on time, I would have taken a few minutes to paint the brackets.   But it doesn’t look that bad when you back up a bit and also see all of the aluminum steering components under the TJ’s front end.  If I get bored some day, I’ll break out a rattle can of flat black and give it a couple of quick coats.  It won’t rust as it is (yet another nice feature of aluminum) so its not critical to get the paint on it any time soon.  You can just barely see the 4 button head allen screws hold the brackets in place in the above photo. 

I’ve had a chance to put some more miles on it since yesterday’s short trip home from the shop.  I did a 70 mile errand around town today and so had a chance to get some more freeway miles and some city traffic as well.

It has made a difference.  My city temps have dropped enough that the fan cooler only cycles once in a while at the stop light.  The freeway run (about 50 miles worth) has the temps around 165~170, which is fine for the middle of a hot August day in Phoenix. 

So, that’s about it for the tranny cooler move.  I’ll call it a success for now until I find something proving otherwise.  I checked my AN fittings and all were nice and dry with no signs of ATF leakage. 

Good trails and remember to TREADLightly!