Adding an aux cooler in series with the radiator cooler is the single best AW4 longevity mod. See cooling section for cooler details.
See cool-trans-cooler entry for full cooler selection and install. The transmission-side notes:
The AW4 burns fluid above 240F. Stop-and-go traffic in summer with a 4.0 working hard (towing, lifted with big tires, A/C on) easily pushes the converter outlet temp to 240F+. The radiator-integrated cooler dumps heat into hot coolant on a hot day, which means it dumps little heat.
An auxiliary stacked-plate cooler in front of the radiator (Hayden 679, B&M 70268) keeps fluid temp 30-50F lower under load. The most expensive transmission failures are heat-related: a $100 cooler prevents a $2000 rebuild.
Installation order: trans -> radiator cooler -> aux cooler -> trans. The radiator cooler still helps by maintaining minimum operating temp in winter — don't bypass it.
Add a temp gauge if you wheel or tow. Knowing your trans is at 220F vs 280F is the difference between continuing and pulling over to cool down. Without a gauge, you'll find out about overheating from a slipping shift or a burned-clutch smell.
| Part | Vendor | Est. price |
|---|---|---|
| Hayden 679 cooler | Hayden | ~$80 |
| B&M 70268 SuperCooler | B&M | ~$100 |
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.