1999–2000 WJs hold about 13 quarts of coolant, 2001–2004 hold about 15 quarts. Run HOAT-rated coolant (Mopar MS-9769 or Zerex G-05) at 50/50 with distilled water — not green ethylene glycol, and not Dex-Cool.
The WJ uses HOAT coolant (Hybrid Organic Acid Technology) from the factory — it's the amber/yellow stuff, not the green or orange. Mixing chemistries is what kills WJ cooling systems: pour Prestone universal into a HOAT system and the inhibitor package precipitates out, the radiator clogs, and you end up replacing a heater core 20,000 miles later. Stick to MS-9769 spec (Mopar HOAT, Zerex G-05, or Peak Final Charge Global) and use distilled water for the mix.
Drain the radiator at the petcock — bottom driver-side corner, white plastic, turn by hand (channel locks if it's stuck, but be gentle, the petcock plastic is brittle on these). Open the radiator cap (cold engine only) so it drains faster. The petcock alone gets ~6 quarts out. To get a real flush you also have to drain the block — there are two block drain plugs on the 4.7L (one per side of the block, hex head, 5/8") and one on the 4.0L (passenger side block, behind the exhaust manifold). Pulling block drains gets the rest of the old coolant out instead of diluting new coolant with old.
Close everything back up, fill with the recommended capacity (13 qt for 1999–2000, 15 qt for 2001–2004) of 50/50 HOAT and distilled water. Burp the air out: idle with the heater on full hot, watch the temp, top off the radiator as the air works out. The 4.7L has a known habit of holding an air pocket near the thermostat — drive the truck through a heat cycle and recheck the overflow bottle the next day.
If you're past the 100,000-mile mark on factory coolant or never know when the last flush was, this is overdue work. Old HOAT coolant turns acidic and eats the radiator from the inside.
| Part | Vendor | Est. price |
|---|---|---|
| Mopar HOAT coolant (MS-9769) — 2 gal | Mopar | ~$40 |
| Zerex G-05 HOAT coolant — 2 gal alternative | Valvoline / Zerex | ~$30 |
| Distilled water (1 gal) | any grocery | ~$2 |
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.