Add a Hayden or B&M trans cooler in series with the OEM radiator cooler. Single best longevity mod for the AW4 in towed or lifted XJs.
The AW4 sheds heat through a small cooler integrated into the radiator end tank. Under load (towing, mud, lifted with big tires, slow trail crawling) that cooler can't keep up — trans temp climbs and oxidizes the fluid. Burned ATF kills clutches.
The fix: a stacked-plate auxiliary cooler plumbed in series after the radiator cooler. Hayden 679 or B&M 70268 are the canonical choices. Mount in front of the radiator on the passenger side using the included brackets and zip ties through the rad fins (don't punch them with the supplied screws — they crush the fins and break the rad).
Plumbing: radiator cooler outlet (lower fitting) -> aux cooler inlet -> aux cooler outlet -> trans return. Use 5/16" trans cooler line with worm clamps doubled at each junction. Run new line, don't reuse 25-year-old rubber.
For serious towing or wheeling, add a temp gauge (Auto Meter or B&M 80212) with the sender in the pan or in a tee fitting in the cooler line. Without a gauge you have no idea if the cooler is doing its job. Target temp: <200F under load. >240F is burning fluid.
The AW4 is bulletproof when kept cool. Most failures are heat-induced.
| Part | Vendor | Est. price |
|---|---|---|
| Hayden 679 transmission cooler | Hayden | ~$80 |
| B&M SuperCooler 70268 | B&M | ~$100 |
| 5/16 trans cooler hose 10ft | Gates | ~$25 |
| B&M trans temp gauge 80212 | B&M | ~$90 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.