We don't trust automatic transmissions, and given our choice, we'd stick with a manual in every Jeep we have. That said, our '98 Cherokee came from the factory with an AW4, and swapping it out requires sourcing of hard-to-find late-model XJ clutch pedal parts and a spendy computer swap to kill the check engine light.
The AW4 is the best overdrive automatic transmission the factory ever put in a Jeep and they commonly can run over 200,000 miles with regular fluid changes. Ours is at 238,000 miles and we recently came to an alarming observation: We are killing it. Don't get us wrong, we are doing everything right: We change the fluid with regularity, we are using Royal Purple ATF, we kick it out of overdrive for long grades or when hauling heavy loads, and we swap filters when we change fluid.
Before you go spending any...
Before you go spending any coin on coolers, hoses, and fittings, check to make sure you have a problem. If you've modified your Jeep with bigger tires, and take it crawling or get stuck in traffic (lack of airflow) odds are good you are running your transmission past its accepted design parameters. We tapped Auto Meter to help us figure some things out. We picked up a few transmission temp manifolds (PN 2286), some full-sweep gauges, and some extra senders (PN 2252). We mounted the manifolds and senders in various places in the system to monitor the temp real-time.
However, we have come to the realization that we are overheating our slushbox and that is the single most common cause of automatic transmission failure. Our beloved manual transmissions aren't nearly as susceptible to heat, but when we installed a DashDAQ in this Jeep we found it was able to monitor an alarming number: the transmission temperature. While going up steady grades at ambient temperatures of 90 degrees or more, our AW4 frequently sees 240-250 degree oil temperatures. It also tops 200 degrees when crawling. According to the factory service manual, the operating range for the AW4 is 125-176 degrees.
For every 25 degrees over the maximum operating temperature, you take about half the life expectancy from the transmission, so our transmission has had its lifespan cut down to about a third of what it should be.
Throw the baby out with the bathwater, that's us. Once the transmission started slipping, we went looking into cooling solutions. It was then we learned all of the handy aforementioned figures. Regardless of what automatic transmission you have, figure out what the operating temperature is supposed to be, put a temp gauge on it, and if needed, fix it before it is too late. We all push our Jeeps further and harder than the original design parameters, and an ounce of prevention is worth a pound of cure.
In this case, we went ahead with a few hundred pounds of cure squeezed into the proverbial 5-pound bag. Yeah, we waited too long to do this. Yeah, we went way gonzo on the cooler size. And, as always, opinions are like... um...well, you know. Use some common sense when protecting your automatic transmission.
Don't listen to the guy who says, "Here is what you need." The reality of it is that the correct way to route your auxiliary cooler depends on your driving style, the weight and build of your Jeep, and your climate. You want that slushbox at that operating range all the time. If that means including the radiator, putting an auxiliary cooler (or two) on it, or running the fluid through an ice box, it's your call. No two applications are the same. Start with installing a temp gauge and go from there.
That said, our '98 XJ is a bit of a porker, we see a lot of freeway mileage with elevation changes, we often haul parts in it (axles, engines, and so on), we live in southern California, and our recreational use of the Jeep sees us many miles off in the desert with camping gear for many days. Our transmission cooling needs might be more than what you need, but we still learned a bunch on our journey, and you will be able to apply some of our tips to your slushbox-powered Jeep for more worry-free mileage.
After we'd confirmed our DashDAQ...
After we'd confirmed our DashDAQ was telling the truth in regards to transmission temperature, we started looking for coolers. We were familiar with the B&M Hi-Tek cooler and the included fan and thermostatic switch made good sense for us. The fan comes on at 175 degrees and shuts off at 140 degrees, which makes it a perfect match for the AW4's intended operating temperature.
Our original plan was to mount...
Our original plan was to mount the cooler to the factory skidplate. We had a B&M Hi-Tek cooler on the shelf that never made it into another project. They are made from aluminum and feature a fin and plate design that handles abuse better than a tube style cooler. The one on the left (PN 70298) is the one we had which features a 7-inch SPAL fan. But that would have been too easy a fit, so we ordered the big boy (PN 70297) with a 91/2-inch fan (right) to make sure the transmission is happy.
Of course, the big mamba-jamba...
Of course, the big mamba-jamba wouldn't fit the factory skidplate like we'd planned, thanks to minor things like the sway bar and steering linkage being in the way. We didn't want to put the cooler in front of the radiator (not that it'd fit with that fan on it), so after much deliberation and fitment estimates, we located it on a custom bracket behind the bumper. It is tight to the bumper, swaybar, and harmonic balancer, but it clears all of them by about 1/2-inch and is reasonably protected. The electric fan will create whatever airflow is needed, and we are hoping the stock overhead console temperature probe isn't affected too much.
The stock AW4 filter isn't...
The stock AW4 filter isn't anything to write home about; we've seen some fishnet stockings with tighter tolerances. So we added a B&M remote filter (PN 80277) to our setup, which we located between the cooler and the power steering box.
We used Earl's fittings and...
We used Earl's fittings and hose to connect it all. We went with black Ano-Tuff hose and fittings to keep the bling to a minimum. The Ano-Tuff coating is a military-spec coating and actually works into the aluminum itself, so even our man-handling and tightening of the fittings with regular steel wrenches didn't mar it. We went with 3/8-inch hose and an assortment of -6 AN fittings.
We wanted nothing to do with...
We wanted nothing to do with the leak-prone factory lines, so we replaced everything from the transmission forward with an assortment of Earl's lines and fittings. The key to attaching an aftermarket line to the AW4 is this 14mm-1.5 to -6 AN adapter (PN 9919DFERL). The O-rings are sold separately, so make sure to order at least two of them. The forward fitting on the transmission is where the hot fluid comes out; the rear fitting is the return.
Once we got everything buttoned...
Once we got everything buttoned back up, we took the Jeep to a local shop and had them flush the old, burnt fluid out of the transmission. We were already running Royal Purple in this Jeep for its resistance to thermal breakdown, but run any automatic transmission at 240-plus degrees for any length of time and even the best ATF will give up eventually. Even though we now had the heat under control, we still wanted the added protection Royal Purple offers for our high-mileage transmission.
We used two Auto Meter transmission...
We used two Auto Meter transmission temperature gauges for our testing. We used PN 5957 with red backlighting to indicate the temperature of the hot fluid coming out of the transmission and PN 3857 with green backlighting to indicate the temperature of the fluid coming out of the cooler. We mounted them in an Auto Meter gauge pod made for the Cherokee (PN 15210). The gauge pod is only available in black, so we painted it with Dupli-Color medium gray Vinyl & Fabric paint to better match our grey interior panels.
If you live in a colder climate...
If you live in a colder climate than we do, you will want to retain the factory cooler that is located in the radiator (green line). Running the transmission lower than the operating temperature can be bad for it as well, but in sunny Southern California our transmission is often at 125-degrees just sitting in a parking spot, so we bypassed it altogether. Our AW4 now runs at 150-160 degrees all the time and the engine runs a bit cooler as well.