0331 Cylinder Head Crack Diagnosis and Remedies
2000-2001 XJ 4.0L heads with casting number 0331 (non-TUPY) crack between cylinders 3 and 4. Symptoms: coolant loss with no external leak, white exhaust, overheat.
The infamous 0331 head casting was used on Jeep 4.0L engines from 2000 through 2006 (TJ and WJ also affected). The specific 'pre-TUPY' versions cracked predictably between the #3 and #4 exhaust valve seats, dumping coolant into the cylinders and onto the exhaust valves. Diagnosis: chronic mild overheating, coolant level drops with no puddle, sweet exhaust smell, white smoke especially on cold start. A compression test may pass while a cooling-system pressure test shows pressurization in the radiator after shutdown. Pull the oil fill cap and look down between the exhaust rockers of cylinders 3 and 4: cast text 'TUPY' visible means a later improved casting (safer); no TUPY text means original 0331 (high failure risk). Remedies in increasing cost: 1) live with frequent coolant top-ups (not a fix); 2) head gasket replacement with a new TUPY 0331 head from rockauto or salvage; 3) swap to an earlier (1991-1999) 7120 casting head, which is the gold standard for non-cracking; 4) head replacement combined with a full rebuild. Always replace head bolts (they are torque-to-yield) and run a fresh coolant fill.
Why it works
- Permanent fix with TUPY or 7120 head
Trade-offs
- Major job
- Some salvage heads also cracked
Tools required
- torque wrench (large)
- head stand
- engine hoist or strong back
- FSM
Parts
| Part | Vendor | Est. price |
|---|---|---|
| Cylinder head (TUPY 0331 or 7120) | Mopar/RockAuto | ~$400 |
| Head gasket Fel-Pro | RockAuto | ~$60 |
| Head bolt set | Fel-Pro | ~$50 |
Sources
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