I've been a follower of this site for some time and am on my 3rd jeep, a 2000 Cherokee sport. I've owned this one for about 3 months now and noticed my coolant overflow resovoir to have quite discolored fluid. This is after a recent coolant flush. Oil in the coolant is my thought. After reading much about the infamous cylinder head scandal plaguing us 00-03 4.0 owners, my thoughts are head related. Oil in the coolant but no coolant in the oil that i can tell. Oil level stays good and no milky appearance. Oil pressures are good. In an attempt to verify an obvious crack, i looked under the fill cap. No obvious crack, but obvious coolant. The coolant was sitting atop the rocker arms and most flat surfaces i could see. Time for action. In searching for new heads, the questions by many of the companies was to verify a 0331 or 0630 casting. My question are they interchangable? According to National Cylinder Head, both have the mounting bosses for the coil pack and from what the computer told them, the only difference being port exhaust port size. My gut says they are not swappable as everyone would just put on a 630 versus sourcing a special year 331. I plan to verify the casting before ordering, just wondering if a 630 is an option for a current 331 if that is what i have. Thanks all in advance.

 

Only the 0331 heads have all the bolt holes for the coil pack.Late 1999-mid 2001 all have the 0331 head, yes you can physically swap them but why start niger-rigging all the parts that would bolt up neatly to a new 0331 head which will be fine cause they have fixed the bad area between clyinders 3 and 4 on the old casting.Good luck I hope you chose to fix it right the first time. but only late 1999-mid 2001 have the bad casting, they started to reproduce a good head casting in 2001 FYI.

 

I have found no confirmation of any 99's with the 0331 head and I have followed up on a few leads. There were a few anecdotal reports, but I don't think they were true.

My understanding is that all 00-01 XJs have the suspect 0331 head.

The fix for the bad 0331 head did not come until late 02 at the earliest. That was when Jeep started to source TUPY heads (brazilian foundry). All 03 and newer 0331 heads for sure are good.

The way to know for sure is to verify. The "fixed" 0331 head has the word TUPY between cylinders 3-4 on the head. If it doesn't say TUPY, you don't want it.

For more information on the 0331, read this thread.

http://www.jeepsunlimited.com/forums...d.php?t=391831

 

I highly doubt that oil in coolant is from the 0331 "normal" head crack.

Where the head cracks is on the coolant galley (pressurized) and goes into the top of the head (not pressurized) where the oil pools and runs across.
The chances of non pressurized oil getting back into a pressurized system is very small.

Describe discolored fluid.... is it just off colored completely? If it has oil contamination the oil will separate from the coolant and float on top.

If it is oily in there I would suspect the internal tranny cooler in the radiator is leaking into the coolant.

Over the years ive had a few different vehicles that no matter what the coolant would stay discolored no matter how well flushed and refilled.


I have never seen a 630 with coil mounts.

 

My 99 has the 0331 head with the mounting bosses for the coil packs. It's been repaired from the PO so I don't really know how it was fixed.
I'm not worried. If it goes I'll get an Alabama head.

 

As you mentioned, it was repaired by the previous owner, who put the 0331 head on it. That 99 originally came with the 0630 head from the factory.

 

I've read repeatedly on this forum and others that the late 99's had the 0331 head and the build date on mine is september of 99. I'm pretty sure it came that way and it was probably a head gasket they changed.
But then again considering how everything else was f'd up on this who knows. How hard do you have to hit the front axle to rip off the lower control arm mounts?

 

RSMART i like your thought on the tranny cooler being suspect as there aren't some of the typical symptoms. Coolant temps, oil pressures, things like this all seem normal. Truck has no power issues and motor runs good. It currently has 108,000 miles. As i mentioned before i got it used from a 1 owner carfax report. When i got it i did the typical fluid/filter changes and noticed the coolant to be an ugly brown color. When the oil was changed i kept the oil in the drain pan to check for seperation of coolant and there was none. Did the coolant flush about 1000 miles ago and noticed some coolant loss that i attributed to air in the system as i added small amounts for the first 500-750 and the level stabilized and held. The current resovoir has brownish coolant with a definite layer of something on top. I had called around the usual vendors i.e. Coldwater and Alabama. I called National Cylinder Head and they quoted a price of about $100 less. At this point i am waiting for some better weather and with the noted symptoms feel ok. Just want to get my ducks in a row while i wait. I am currently having trouble verifying the casting number as 331. What yoga like position is needed to see this under/over the engine?

 

It's right below the fuel rail somewhere between 3 and 5 I think. It's on the casting just off where the valve cover sits.
It's also not stamped but cast right onto the head during manufacture.

 

Jamie, thank you. Thats what i thought. This area is covered with the foil covered insulation and i pulled it aside as best as i could without destroying it. Ill get more in depth. This site is such a wealth of information ranging from the guy who struggles with changing oil to the folks who teardown/rebuild often. I consider myself a competant mechanic and a head swap is not off the radar. Inconvenient? yes! Insurmountable? No!. Just might need an extra beer or so on standby. I'm sure during this job i'll run into another ? and i'm sure ill refer back quite often for input. Thanks again to all for your help.