Are all 0331 heads bad for all year 4.0's

xjtrailrider · Nov 17, 2008

I just picked up a "free" low mileage 4.0 that is obviously from a WJ or TJ due to the oil filter being screwed directly into the block. I only hear of the 00' XJ 0331 being bad but not other models.

So my question is are all 0331's supposedly time bombs.

Also can someone cross these numbers from the block and tell me exactly what year 4.0 this is

810MX21

xjtrailrider · Nov 17, 2008

I forgot to add that is a "distributor less" model and has the screw holes for the coil packs in the head. I didn't get the intake or TB with the long block, but hey it was free so who was I to argue!

5-90 · Nov 17, 2008

If it's an 0331 head, it's got COP/DIS from the factory (that was the only head that had the bosses for it.)

I'm wanting to think that the problems were ironed out around the end of 2001 or so, and I'd like to get castings on both sides of that line to section and check out. I don't know how to tell them apart - except for a possible "time-date clock casting" you sometimes see, but I've not had any later heads handy to look at.

The going consensus is that the 2000/2001 XJ w/0331 and the 1999-2001 TJ/WJ heads have about a fifty-fifty shot at cracking between the #3 and #4 cylinders - they're fine after that (and it was the #0630 head before that, which is generally regarded as acceptable.)

xjtrailrider · Nov 17, 2008

5-90 said:
If it's an 0331 head, it's got COP/DIS from the factory (that was the only head that had the bosses for it.)

I'm wanting to think that the problems were ironed out around the end of 2001 or so, and I'd like to get castings on both sides of that line to section and check out. I don't know how to tell them apart - except for a possible "time-date clock casting" you sometimes see, but I've not had any later heads handy to look at.

The going consensus is that the 2000/2001 XJ w/0331 and the 1999-2001 TJ/WJ heads have about a fifty-fifty shot at cracking between the #3 and #4 cylinders - they're fine after that (and it was the #0630 head before that, which is generally regarded as acceptable.)

Thanks 5-90. I just found the casting date on the block, 9-10-99, so its a early model for the COP/DIS.

I'm going to pull the head/pan and check everything over good but this engine is very clean, looks hardly run. It has been in storage for several years.

5-90 · Nov 17, 2008

xjtrailrider said:
Thanks 5-90. I just found the casting date on the block, 9-10-99, so its a early model for the COP/DIS.

I'm going to pull the head/pan and check everything over good but this engine is very clean, looks hardly run. It has been in storage for several years.

If it's the head that came on that block, then you've still got a 50/50 shot at having it crack on you. Good news? You can still switch to an 0630 or a 7120 - it takes a little doing (fab bracketry for the coil rail and you'll want an adapter plate for the exhaust ports,) but it's doable.

Are all 0331 heads bad for all year 4.0's

xjtrailrider

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xjtrailrider

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5-90

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xjtrailrider

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5-90

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