WJ, is that a grand Cherokee? Plenty of those POS laying around Pull My Part

 

Is this a good casting?

http://www.ebay.com/itm/Engine-Cylinder-Head-CYLINDER-HEAD-MOORES-Reman-fits-99-06-Jeep-Wrangler-4-0L-L6-/231167906335?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A2004%7CModel%3ATJ&hash=item35d2ae521f&vxp=mtr

 

The casting number is not visible or mentioned in the listing. I wouldn't buy a rebuilt one of these, after reading up on these bad heads. Usually when they try to fix the cracked ones, they break again from all I've read.

 

Ok, we have a winner here.
Friday I checked the oil cap before returning home. It had a jelly like substance in it and some drops of condensation. Still no coolant in the oil when checked.

I suspect I have a small crack in the top of the head exposing the coolant in the form of steam to the valve cover, thereby evaporating it. Sux but I was actually relieved to find it.

So, where can I get a head from a 04-06 TJ that does not have the 0331 casting?

 

All heads past mid year 99 are 0331 castings .... They updated the design in late 02 to the TUPY version which solved the issue.
So an 03 or newer head would be bolt in.
Or you can use an earlier head and make some exhaust changes.

 

What changes all of the sudden made these heads start cracking? Cats causing more back pressure/heat?

 

A complete redesign of the casting.... Port layout on the exhaust side, overall thicknesses, etc....
The TUPY casting merely added material back into the compromised section, so my guess is they cut too much fat off and were left with just bones and no meat so to speak.
The casting is exceptionally thin in the 3/4 area compared to previous castings. Weight saving to improve MPG most likely.
The Precats showed up mostly in mid 00, and we're standard after that. My 00 did not have them, but I know of other Canadian 00's that did.

 

There were two emissions versions of the XJ in 2000, a California version meant to comply with stricter CA law, and a 49-state EPA version that met the less stringent federal standards. The precats are on 2000 XJs with CA emissions. The EPA emissions vehicles did not have the precats. In 2001 Chrysler did away with the EPA version altogether and only sold the CA emissions vehicles, all of them with precats.

As Rockfrog said, it was a casting with a weak spot. It happens on some '99s as well, even though it still had the single downpipe with no precats. I have a 2000 EPA version with no precats, and mine cracked. Unfortunately the problem didn't usually make itself known until the trucks were well out of warranty, so Chrysler got away with turning a blind eye to it without issuing a recall. At least they fixed it on the later 4.0L engines, but that doesn't help the rest of us.