Cherokee XJXJ 4.0 Head Gasket Failure: Signs, the 0331 Crack, and What It Really Costs
Your coolant keeps disappearing with no puddle on the driveway, the oil cap is wearing a milky tan film, or there is sweet white steam trailing the tailpipe. On a 4.0 Cherokee that pattern points to a failed head gasket — and if your XJ is a 2000 or 2001, there is a strong chance the head itself is cracked. Here is how to read the signs, how to confirm which one you have, and what the repair actually runs.
A failed head gasket on a 4.0 shows up as coolant vanishing with no external leak, milky oil on the dipstick or cap, white sweet-smelling steam from the exhaust, overheating, and bubbles in the radiator with the engine running. The cast-iron block almost never fails — the weak point is the aluminum head. On 2000–2001 XJs (and some early 2002s) the failure-prone head is the one cast 0331, which cracks between cylinders 3 and 4 where the casting walls were made too thin. Confirm gases in the coolant with a combustion leak test, then plan to pull the head: a good head gets a gasket and goes back on, a cracked 0331 gets replaced with a 2003-or-later casting. Parts run roughly $40–$120 for a gasket set; a remanufactured head adds $300–$600. Do not keep driving it — coolant in the cylinders or oil can turn a gasket job into a engine.
What head gasket failure feels like on a 4.0
The 4.0 rarely fails quietly. The most common first symptom is coolant loss with nothing on the ground — you top off the overflow, and a week later it is low again with no puddle, no hose weeping, no radiator stain. The coolant is going somewhere it should not: into a cylinder, where it burns off as steam, or into the oil. Pull the dipstick or pop the oil cap and look for a tan, milky, mayonnaise-like film. That is coolant emulsified into the oil, and it is one of the clearest tells that combustion and cooling have crossed paths.
From there the signs stack up. White steam from the tailpipe that smells faintly sweet is coolant burning in the chamber — not to be confused with the harmless water vapor every engine puffs on a cold morning, which clears once the engine warms. Persistent overheating, especially under load on a grade or on the highway, follows as the system loses coolant and traps combustion gas in the jacket. With the radiator cap off and the engine idling, bubbles rising steadily in the coolant are exhaust gas pushing past the failure. And the temperature gauge that climbs and then dumps coolant out the overflow on a hot run is the same story from the dash. Any one of these on its own is worth a closer look. Two or more together, and you are almost certainly there.
The 0331 head: why some XJs were built to crack
Not every 4.0 head gasket story is a gasket. On 2000–2001 Cherokees, and some built into the first half of 2002, the cylinder head itself is the problem. Those years used a head cast with the number 0331, and the casting walls between cylinders 3 and 4 were made too thin. Under repeated heat cycling those walls crack — sometimes between the combustion chamber and the water jacket, sometimes between an exhaust port and the jacket, sometimes only between the jacket and the crankcase. The symptoms mimic a blown gasket exactly, which is why so many owners replace a gasket, button it up, and watch the coolant vanish again a month later.
Where the crack sits decides what you feel. A crack into an exhaust port pushes steam out the tailpipe while the engine otherwise runs fine. A crack into an intake port or combustion chamber can make the engine stumble like it is down a cylinder. A crack that only reaches the crankcase gives you the mystery coolant loss with no other drama. To check your head, look on the driver's side casting between the spark plugs and the exhaust manifold for the raised number. If it reads 0331 and the Jeep is a 2000 or 2001, treat a coolant-loss problem as a cracked head until a teardown proves otherwise. Jeep recast the head for 2003 — often marked TUPY — and that revision fixed the issue, which is why the 2003-and-later head is the one you want as a replacement.
Head gasket or cracked head? Confirm it before you tear in
Here is the honest part: from the symptoms alone you usually cannot tell a blown gasket from a cracked head, because both do the same thing — they let exhaust gas into the coolant and let coolant into places it should not be. So before you order parts, confirm the failure is real. The fastest at-home test is a combustion leak test, sometimes called a block test. You add a test fluid to the radiator, draw air from above the coolant through it with the engine running, and watch the color: blue or fluorescent fluid that turns yellow means exhaust gases are in your coolant. It is a roughly $30 kit and it converts a guess into a yes-or-no. A combustion leak test kit is the single most useful thing to have on the bench before you commit to the job.
A cooling system pressure test is the useful companion. Pump the system to the cap's rated 14–16 psi and watch for ten minutes: pressure that bleeds off with no external leak points at an internal one. What neither test does is tell you the source — gasket or head. That answer only comes once the head is off and a machine shop checks it for flatness and Magnafluxes it for cracks. This is why the 0331 detail matters so much: if your casting is a 0331 and the Jeep is a 2000–2001, the smart money assumes the head is cracked, and you plan to replace it rather than reuse it. Spending a weekend installing a fresh gasket under the same cracked head is the most common way XJ owners do this job twice.
What the fix actually costs
If the head is good and only the gasket failed, this is one of the better-value repairs on the platform, because the 4.0 block underneath is famously durable. A complete head gasket set with the new gasket, intake and exhaust manifold gaskets, and seals runs roughly $40 to $120 depending on brand. The widely used set for this engine is the Fel-Pro HS 26224 PT head gasket set, which comes coated for a dry install. Add a set of fresh head bolts, since the factory torque-to-yield approach means reused bolts are a gamble. Plan on new coolant and an oil-and-filter change after, because the contaminated oil has to go.
If the head is cracked — or warped from the overheating that caused the failure — the math changes. A remanufactured or known-good replacement head adds roughly $300 to $600, and a 2003-or-later casting is worth seeking out over another 0331. A machine shop checking and resurfacing your existing head, if it is salvageable, is cheaper but only makes sense on a head that is not a 0331. Done in a home garage over a weekend, the whole job is parts and your labor. Farmed out to a shop, expect the labor alone to run several hundred dollars on top. The deciding factor is almost always the head, not the gasket — which is exactly why confirming the casting number before you buy anything saves the most money.
If you do the job: the torque sequence that matters
The 4.0 head gasket installs dry — no sealer on the gasket face, because the coating is already there to do that work. The part people get wrong is the bolt torque, and getting it wrong is how a fresh gasket leaks again. There are 14 head bolts, tightened in the factory sequence in three passes: first every bolt to 22 ft-lb, then every bolt to 45 ft-lb, then the final pass. On that final pass bolts 1 through 10 and 12 through 14 go to 110 ft-lb. Bolt number 11 — the short one — is the exception: it torques to about 100 in-lb, which is only a fraction of the others. Pull bolt 11 to 110 ft-lb like its neighbors and you will strip or crack something, so set your wrench down and use the right value for that one. Coat bolt 11's threads with thread sealant, since it enters a coolant passage.
Always work the sequence, never a circle, and bring every bolt up evenly across the passes so the head seats flat. Confirm the deck surface is clean and the head checked flat before it goes on — a warped head will leak no matter how perfectly you torque it. None of this is beyond a capable home mechanic with a torque wrench and a service manual, but it rewards patience over speed. The reason this engine has a reputation for going 300,000 miles is that the people who rebuild the top end take the bolt sequence seriously.
- Signs: coolant loss with no puddle · milky oil · sweet white tailpipe steam · overheating · bubbles in the radiator
- Weak point: the aluminum head, not the cast-iron block
- The bad head: casting 0331, 2000–early 2002 — cracks between cylinders 3 and 4
- Replacement head: 2003-or-later casting (often marked TUPY)
- Confirm with: combustion leak (block) test for gases in coolant; pressure test for internal leaks
- Parts cost: gasket set ~$40–$120; reman head adds ~$300–$600
- Torque: 22 → 45 → 110 ft-lb in sequence; bolt 11 only ~100 in-lb — do not overtighten it
The honest verdict
A head gasket failure on a 4.0 is not the end of the Jeep — it is one of the most worthwhile repairs the platform asks for, because the block underneath is built to outlast almost everything bolted to it. The trap is not the gasket; it is the 0331 head. Replace a gasket without checking the casting on a 2000–2001 XJ and you stand a real chance of doing the whole job again. Pull the head, have it checked, and if it is a cracked 0331, put a 2003-or-later head on instead of feeding the same flaw back into the engine.
Two rules will save you the most grief. Stop driving once you suspect it — coolant entering a cylinder or diluting the oil can score a bore or wipe a bearing, and that turns a parts-and-a-weekend job into an engine. And confirm before you spend: a $30 block test and a two-minute look at the casting number decide whether you are buying a gasket set or a head. Get those two things right and a 4.0 with a blown gasket has a very long road left in it.