MajorCommonEngine

Jeep Wrangler: Cracked 0331 cylinder head between cylinders 3 and 4 (4.0 inline-six)

Cracked 0331 cylinder head between cylinders 3 and 4 (4.0 inline-six) is a common engine fault on the Jeep Wrangler on the 2000–2002 cars, and we rate it major. Putting it right costs $3,000 to $5,500 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 24 documented faults on the Jeep Wrangler.

Vehicle: Jeep Wrangler
Engine: 4.0L
Years: 2000–2002
Fuel: petrol
System: Engine

This page covers the Jeep Wrangler as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Jeep Wrangler faults24 documented faults on this model

What you are looking at

What goes wrong

The 4.0 inline-six in 2000 to 2002 TJs used a redesigned cylinder head (casting number 0331) with thin walls between cylinders 3 and 4, and early castings are widely reported to crack there, usually after 200,000 km or more. The first sign is unexplained coolant loss with no visible external leak; left alone, coolant gets into the oil and the engine can overheat or suffer bearing damage. The casting was improved during 2002 (the later heads still carry the 0331 number), so 2003 to 2006 cars are much less affected. There was never a recall or extended warranty; the usual fix is a new redesigned aftermarket head.

What you would notice

Coolant level keeps dropping with no puddle under the car
Milky or light brown sludge under the oil filler cap
Sweet coolant smell or white exhaust smoke after warm-up
Temperature gauge creeping up on long climbs
Oil pressure gauge reading lower than normal once warm

How to check it

Where to look. Top of the engine under the valve cover, in the middle of the cylinder head between cylinders 3 and 4

With the engine cold, open the bonnet and check the coolant level in the overflow bottle and, if the seller allows, in the radiator itself. A bottle that is low or recently topped up is a warning sign. Pull the oil dipstick and remove the oil filler cap and look for milky or mayonnaise-like residue. Start the engine and watch the exhaust for white, sweet-smelling smoke once warm. On the test drive, watch the temperature and oil pressure gauges on the dash; they should stay steady. Ask how often coolant is topped up and whether the head has been replaced, and ask for the invoice. If a workshop inspection is possible: have the cooling system pressure tested and a combustion gas (block) test done on the coolant, and have the head checked for the crack between cylinders 3 and 4.

Parts involved: Cylinder head.

What it costs to put right

$3,000 to $5,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“How often do you need to top up the coolant?”
“Has the cylinder head been replaced, and was it a new redesigned head?”
“Has it ever overheated?”

Now check the Jeep Wrangler you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

WranglerTJForum: Newbie doing the 0331 cracked cylinder head replacement
WranglerTJForum: How can I tell if I have the cylinder head that is prone to cracking?
WranglerForum: FYI checking when buying a used TJ for cracked head, coolant leak
JeepForum: Early 0331 Heads (TJ 2000 and 2001)

Jeep Wrangler buyer questions

Is cracked 0331 cylinder head between cylinders 3 and 4 (4.0 inline-six) serious on a Jeep Wrangler?

We rate it major and common on the Jeep Wrangler. The 4.0 inline-six in 2000 to 2002 TJs used a redesigned cylinder head (casting number 0331) with thin walls between cylinders 3 and 4, and early castings are widely reported to crack there, usually after 200,000 km or more. The first sign is unexplained coolant loss with no visible external leak; left alone, coolant gets into the oil and the engine can overheat or suffer bearing damage. The casting was improved during 2002 (the later heads still carry the 0331 number), so 2003 to 2006 cars are much less affected. There was never a recall or extended warranty; the usual fix is a new redesigned aftermarket head.

How much does it cost to fix on a Jeep Wrangler?

$3,000 to $5,500 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Jeep Wrangler years are affected?

Our research records this fault on the 2000–2002 Jeep Wrangler. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.