Drain the radiator, flush with distilled water until clear, then refill with the correct Mopar coolant for your year — HOAT for 2007–2012, OAT for 2013+. The two chemistries are not interchangeable.
The JK cooling system holds about 11.4 quarts when fully dry, but a drain-and-fill through the radiator petcock only swaps roughly 8 quarts. That is enough to refresh the chemistry on a healthy system every 5 years or 60,000 miles. If you are chasing a contamination problem — sludge, rust color, oil sheen — you need a full flush with distilled water, not a straightforward drain.
The single most important rule is matching coolant type to model year. 2007 through 2012 JKs were filled with HOAT (Hybrid Organic Additive Technology — Mopar's pink coolant). 2013 through 2018 JKs switched to OAT (Mopar MS-12106, purple). Chrysler says explicitly that mixing the two causes accelerated corrosion and seal failure. If you are not sure what is in the system, flush it completely with distilled water before adding new fluid.
A few JK-specific notes that catch people. The petcock on the lower radiator passenger side is plastic and brittle — turn it gently, replace it if it weeps after reinstall. The pressure cap sits on the coolant bottle, not the radiator. The 3.6L Pentastar (2012+) is fussy about air pockets — leave the cap off, run the engine to operating temperature with the heater on full hot, and top off the bottle as the level drops. Skipping the bleed step is how people end up with a hot gauge two days later.
For a full flush: drain at the petcock, then run a garden hose through the upper radiator hose port with the engine off and the lower hose disconnected. Flush until the water runs clear. Reconnect, refill with 50/50 premix to the MAX line on the bottle, run to temperature with heater on high, and top off again after cooldown.
| Part | Vendor | Est. price |
|---|---|---|
| Mopar HOAT (pink) 50/50 premix — 2007-2012 only | Mopar | ~$22 |
| Mopar OAT (purple/MS-12106) 50/50 premix — 2013+ | Mopar | ~$24 |
| Distilled water (1 gallon, for top-off and flush rinse) | 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.