AW4 Transmission Cooler 1984-2001

If the cooler in front of the radiator on your Jeep Cherokee XJ is weeping red fluid, has crushed fins from trail or road debris, or the AW4 runs hot pulling a trailer, this is the part you are looking for. It is a used factory-style auxiliary transmission oil cooler for the AW4, the long tube-and-fin core that sits ahead of the radiator, shown with its mounting brackets and short hard line ends attached. Replacing a damaged one with a factory-style unit keeps the original line routing and mounting points, so nothing has to be adapted.

What the auxiliary cooler does on an AW4

Every XJ with an automatic has a main cooler built into the radiator tank. Jeeps ordered with heavier cooling or towing equipment also got this air-to-oil auxiliary cooler. Jeep's 1997 Cherokee service manual describes it mounted in front of the radiator on the driver side, behind the grille, and explains that fluid leaving the AW4 passes through the radiator cooler first and then the auxiliary cooler before returning to the transmission. That second pass matters because the AW4 makes its heat in the torque converter and clutches, and hot fluid is what glazes clutches, hardens seals and varnishes the valve body. The same manual lists a missing auxiliary cooler and blocked airflow to it, from a plow, bug screen or front-mounted spare, as causes of overheating in towing service.

Symptoms of a bad auxiliary cooler

• ATF dripping from the front of the Jeep, usually at the cooler fittings or a rubbed spot on the core
• Bent or packed fins that block airflow, so fluid temperature climbs on hills or in traffic
• Dark, burnt-smelling fluid after towing, which the service manual ties to restricted flow through the main or auxiliary cooler
• Low fluid level with no leak at the pan, case or lines at the transmission
• Slipping or late shifts once the AW4 is hot, from the fluid level falling or the fluid breaking down

How to confirm before you buy

Clean the front of the cooler and its fittings, run the engine in Park and look for fresh wetness. Check the fins: a cooler that is half flattened cannot shed much heat. Then check the AW4 fluid level and condition with the engine running and warm. If the fluid is dark with debris, the transmission may already be damaged, and the service manual calls for reverse flushing both coolers and the lines after any failure that makes sludge or friction material. A worn unit needs attention first; our AW4 overhaul gasket and seal kit and AW4 lockup solenoid are the usual starting points when heat has caused problems.

Fitment

The listing covers 1984-2001, but the AW4 itself arrived for the 1987 model year in the Cherokee XJ and Comanche, so this cooler applies to AW4-equipped Jeeps from 1987 through 2001. Earlier XJs used different transmissions. Brackets and line ends changed over that long run, and Jeep listed separate cooler lines for 1987-1996 4.0L XJs with the auxiliary cooler, so compare the bracket holes and fitting ends on your old cooler with the photo before you order. If you are not sure, send us your year and VIN and we will check it. Our Aisin transmission parts page lists the other AW4 parts we carry, including the AW4 valve body.

Install notes

• On the 1997 XJ, Jeep's procedure removes the front bumper and the radiator support to reach the cooler lines and the attaching bracket. Plan your time around that.
• This is a used part. Reverse flush it before installing, and flush the radiator cooler and lines too if the old fluid carried debris.
• Keep the factory flow order: from the transmission to the radiator cooler, then through this cooler, then back to the AW4.
• Use new hose clamps on any rubber sections and start each fitting by hand.
• Refill with Dexron IIE/Mercon-type ATF, the fluid Jeep specified for the AW4, and check the level hot with the engine running.

If the transmission ran hot long enough to firm up the shifts or slow the engagement, a AW4 shift kit reduces clutch slip and the heat that comes with it.

Will this fit my 1985 Cherokee?

Only if it has been converted to an AW4. The AW4 was introduced for the 1987 model year, so this cooler is meant for 1987-2001 AW4 Jeeps.

Is this the cooler inside the radiator?

No. This is the separate auxiliary air-to-oil cooler mounted in front of the radiator. The main cooler is built into the radiator tank and is replaced with the radiator.

Is the cooler new?

No, it is a used factory-style cooler, shown with its brackets and line ends. Flush it before installing it.

What fluid does the AW4 take?

Jeep specified Mopar Dexron IIE/Mercon for the AW4. The 1997 manual lists an approximate refill capacity of 8.0 liters for an overhaul, but always set the final level on the dipstick with the transmission hot.

My Jeep never had an auxiliary cooler. Can I add this one?

Yes, but you will need lines to route fluid from the radiator cooler outlet through this cooler and back to the transmission, plus a mounting spot ahead of the radiator. Send us your VIN and we can help match the parts.