Hello all. I have a 99 XJ and my wife has an 04 WJ, both have the 4.0 motor. The old XJ seems to need alot more work so i tend to hang out over in the XJ forums but..there's alot of talk over there of 2000/2001 XJ's with cracked heads, the 0331 heads with coil packs. I was wondering if the WJ's were having head cracking problems as well as i think i'd read that WJ had the 0331 head all the way thru 2004.

 

The XJ from 2000 to 2001 had the 0331 head, and the WJ from 99 to 04. Somewhere around the 2003 model year they changed where the head was cast at. 2003 and up should have the better head. Take off your oil cap and look straight down and the letters "TUPY" should be cast in the head. This is the better 0331 head. An older 4.0 with the early 0331 head could have already been changed in the past. Just pull the cap and check.

 

The '04 WJ should have a Tupy 0331 on it. The Tupy foundry in Brazil started supplying the 0331 heads in mid-2002 and added nickel to the alloy to prevent cracking. Although any head can crack if abused, the Tupy heads are not known to be susceptible to the spontaneous cracking of the original casting 0331. They are as durable as the 0630 and 7120 heads of earlier years.

You can verify that it has a Tupy head by looking for the word "TUPY" cast into the top of the head between the #3 and #4 cylinders. You can see it there by looking down through the oil filler hole. The only reason your '04 might not have a Tupy head on it is if the Jeep has had an engine or head swap from an earlier WJ. That's probably not very likely.

 

thank you very much for the info. Its our well maintained 2wd family vehicle. Not abused, no overheating issues or coolant loss problems. Was just wondering if it was something i needed to worry about and sounds like I'm safe with my stock unmolested original '04 motor.

 

This is the good one; replacement started during the 2002 production run.

 

The thing is jeep got a new head and put it on everything with a 4.0The xj was 00-01 the wj 99 to mid 02 and the tj its hard to get a straight answer but 00- mid 02 is about what i can find on them.Your wifes wj has the upgraded head id be more worried about the trans then the head.But if its well taken care of and drove normal it should last a long long time.

 

About the 42re, mine has 225K miles on it without any trouble, just with normal fluid and filter changes every 50K miles. It will decide to not move too well on cold startup unless you slip it into neutral for a minute or two and let it warm up a bit, especially in extreme cold. After that, shifts are on time and solid without any sign of slippage.

It's like me, I have to get the kinks out of my joints in the morning before I can do anything else, old fart that I am!

About the head. Been there, done it! Mine cracked into an exhaust port, not into the valve area, luckily. It was steaming heavily and coolant was dripping out of the exhaust pipe, but none got into the oil. I put a "Clearwater" head on it. $455 complete with valves and springs, including shipping both ways. This head is a heavy duty casting with more metal underneath the valve spring pockets. It weighs 7 lbs more than the stock 0331. Shipping weight was 85 lbs. Return shipping weight in the same packaging was 78 lbs.

What happened here is Chrysler redesigned the intake and exhaust passages for a smoother flow and in doing so, created weak spots in the head. They disavowed this and claimed the cracking was due to overheating or poor maintenance. BS! If that's the case, why did they fix the problem? The higher percentage of nickel makes it tougher and more flexible.

 

They also replaced the earlier one-piece steel exhaust manifold with a split, two-piece design made of cast iron. The crack usually happens between the #3 and #4 cylinders, right near the gap between the exhaust manifolds. That design must put different stresses on the head from earlier manifolds, both from the way the weight is slung and from uneven heating and cooling cycles. The material of the manifold will heat and cool differently, heat rising up from the exhaust will be distributed differently through the gap, and having two regions of stress with a potential relief gap in the middle between the manifolds seems like it would have a tendency to want to bend or warp the head there. I can't help but wonder whether the manifolds contribute to the problem, or could possibly be the actual cause.

 

Anything's possible. I do know the cast iron manifolds hold the heat longer and cause the fuel in the rail to boil after you shut it down and have no airflow to disperse the heat. My WJ was recalled for a heat shield for this reason. All it is is an aluminum wafer blanket that fits around the injectors and covers the area under the fuel rail.

The main reason for the iron manifolds is they get hotter because of the twin cats and steel headers would burn out easier.

 

Personally, my 42re scares the crap out of me. I'm a mopar fan, been drivin Dakota's since 1991, and my wifes 2001 Dakota with 198k miles was on it's 3rd 42re, even with routine fluid and filter changes. Knowing there's another one in the family worries me.

 

Don't get me wrong! I'm babying this one, letting it warm up in neutral, making sure it's stopped rolling before shifting to reverse or visa versa. I use engine braking in lower gears on hills or going up steep ones in lower gears. I also make sure it's engaged before stomping on the skinny pedal. I haven't used WOT more than a dozen times in the 5 years I've owned it, mostly to get out of trouble on on-ramps. Every Sunday she carries about 600 to 700 lbs of newspapers. But it's always in the back of my mind that she's on borrowed time. This Thanksgiving she'll have around 1500 lbs of papers aboard!

 

Just looked for the "0331" casting number on my 01 WJ because a buddy mentioned it's a common problem. It's not between 3 and 4 but further down around 5 and it's "236". Those are the only cast numbers on the head top rail, drivers side. Looking down into the oil fill there isn't a "TUPY casting. The engine overheated because the fan relay puked. The head was magna fluxed, good to go. GC was built 9/2000. I'll assume it's a replacement, has the bolt bosses for the COP/DIS mounting. Just another odd ball casting number to throw out there.

I'm a Land Rover/Binder/Jeep CJ guy, this is my first project Jeep in 24 years...... used to trouble. 205k on it and it rides like a tug boat.

 

I think you might need to look again. A 236 casting is a head for a big block Chevy.

 

The casting number appears in the "TUPY" identifier photo I posted. Upper left corner. If you don't have numbers there, it might be an aftermarket head of some sort. I have the Odessa "Clearwater" head on mine, but currently it's covered in snow and I ain't going out there and clean it off just to check for you! Sorry!