Full system holds about 12 quarts (3 gallons) of a 50/50 mix. Use HOAT (Mopar G-05/Zerex G-05) for 1999+, IAT green for earlier years; never mix chemistries without a full flush.
XJ cooling systems hold roughly 12 quarts (11.4 L) including heater core and block. Drain points are the radiator petcock on the driver lower tank and the block drain on the passenger side rear of the block above the starter (often seized; many skip it). For 1984-1998, factory fill was conventional IAT green ethylene glycol. From 1999 onward, Mopar specified HOAT (G-05, sold as orange/amber by Zerex or Mopar). Mixing IAT and HOAT produces sludge that clogs heater cores; if switching chemistry, run two distilled-water flushes first. Mix 50/50 with distilled water only - tap water minerals precipitate on the head and form hot spots. After refill, run with the heater on full hot and the radiator cap off until the upper hose is warm and bubbles stop, then top off. The 4.0L has no bleed screw, so park nose-up on a ramp to burp air through the radiator neck. Watch the temp gauge for the next two heat cycles to confirm air is fully purged.
| Part | Vendor | Est. price |
|---|---|---|
| Coolant G-05 HOAT (2 gal) | Mopar | ~$30 |
| Distilled water (3 gal) | grocery | ~$5 |
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.