A stock TJ 4.0 radiator lasts 10–15 years before internal corrosion or plastic-end cracking becomes the failure mode. The replacement is a straightforward 2-hour job — budget aluminum upgrades from Mishimoto are worth the price on any TJ seeing trail or tow use.
The TJ 4.0L runs a two-row aluminum core with plastic end tanks from the factory. The end tanks crack at the crimp joint — usually the lower tank, often after 10+ years or 120,000+ miles. Signs of failure: coolant dripping from the lower radiator area, slow coolant loss with no leak visible until the engine is running, or visible green or orange staining on the lower hose fittings. A pressure test will confirm it.
Aftermarket aluminum radiators (both end tanks and core are aluminum) cost $90 to $120 for standard replacements — essentially the same price as OEM-spec units. The plastic-tank failure mode goes away entirely. For a TJ used for towing, off-road summer use in hot climates, or with an engine that runs warm, the Mishimoto Performance unit ($280) has a 3-row core that noticeably drops operating temps. Unless you're tracking temps and finding headroom, the standard replacement unit is fine.
Don't chase overheating with a new radiator if you haven't verified the thermostat, water pump, and fan clutch are working properly. A failing fan clutch causes overheating at idle and slow-speed crawling on hot days — the symptom pattern the TJ is famous for.
1. **Let the engine cool completely.** Never open a hot cooling system — the pressurized coolant will cause burns.
2. **Drain the coolant.** Open the petcock at the lower driver's side of the radiator and drain into a clean pan. Dispose of coolant properly — don't pour it on the ground. Coolant is toxic to animals.
3. **Disconnect the upper and lower hoses.** Loosen clamps, twist and pull — a strap wrench helps on stubborn hoses. Have rags ready.
4. **Disconnect the transmission cooler lines (if automatic).** Use a flare-nut wrench if possible to avoid rounding the fittings. Cap the lines.
5. **Remove radiator shroud bolts and upper mount bolts.** The shroud (fan surround) typically lifts off with the radiator. The radiator mounts to a top bracket with two 10mm bolts and sits in rubber lower cushions.
6. **Lift the radiator out.** Watch the fan blades — they're close. Tilting the top toward you clears the fan.
7. **Install the new radiator.** Seat in the lower cushions first, then bolt the upper bracket. Reconnect transmission cooler lines if applicable.
8. **Reinstall hoses and fill with coolant.** Fill slowly — the 4.0 system holds about 11 quarts. Fill, run to operating temp, check level after bleeding any trapped air pockets.
9. **Pressure check.** Use a radiator pressure tester to confirm no leaks before driving.
OEM-spec replacement radiator: $90–$120. Performance aluminum (Mishimoto): $275–$300. Coolant: $22–$28 for premixed. Full cooling system service (radiator + hoses + thermostat + flush): $150–$200 in parts — a reasonable 3-hour Saturday job on a high-mileage TJ.
| Part | Vendor | Est. price |
|---|---|---|
| OSC Radiator — 4.0L TJ (4-cylinder models use different part) | OSC Automotive | ~$90 |
| Spectra Premium CU2521 aluminum radiator | Spectra Premium | ~$105 |
| Mishimoto Performance aluminum radiator — TJ 4.0 | Mishimoto | ~$280 |
| Prestone 50/50 premixed coolant | Prestone | ~$22 |
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.