Both AMC engines in the CJ-7 hold around 11 quarts (258) to 14 quarts (304) of coolant total — and the radiator drain only pulls about half of that. To do a real flush, you have to drain the engine block too.
The mistake most owners make is opening the radiator petcock, letting two gallons run out, refilling, and calling it done. The radiator on a CJ holds maybe 5 quarts. The rest sits in the engine block, the heater core, and the hoses. If you only drain the radiator, you're diluting old coolant with new — not flushing.
A real flush means opening the block drains on both sides of the engine (under the exhaust manifolds, straightforward to miss) or pulling the lower radiator hose. With the block open, you can run a garden hose into the radiator filler neck and watch the rusty water come out the bottom until it runs clear. Then you close everything up and refill with 50/50 distilled water and concentrated antifreeze.
Coolant chemistry on these engines is forgiving. Stock spec was green ethylene glycol. Universal "compatible with any color" formulations (Prestone AF2100, Peak Long Life) are fine. Avoid mixing Dex-Cool (orange, GM) with green in the same system — the byproducts can clog the heater core. If you're not sure what's in there, drain everything and start with one type.
Thermostat: stock is 195°F. If your engine runs hot in summer Phoenix-style heat, a 180°F thermostat (Stant 13558) buys 15°F of headroom — but a thermostat doesn't fix a clogged radiator or a worn water pump. Diagnose the cause first.
Distilled water matters. Tap water leaves mineral deposits in the radiator core that build up over years. If you're spending $40 on antifreeze, spend $4 on distilled water — don't undo the work.
| Part | Vendor | Est. price |
|---|---|---|
| Prestone DEX-COOL 50/50 Premixed Antifreeze (universal green-compatible) | Prestone | ~$18 |
| Stant 195°F thermostat (AMC 258 / 304) | Stant | ~$12 |
| Gates upper radiator hose (CJ-7 258) | Gates | ~$25 |
| Distilled water (mix at 50/50 with concentrate) | any grocery store | ~$4 |
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.