I had a loss of coolant problem with my 95ZJ, I was worried about all of the usual big ticket items that could be causing the problem. Then I noticed once the coolant gets to a certain level in the resrvoir I would not lose any more no matter how long it had been. I was happy to find it was only a crack in the resrvoir that would let coolant spill out a little on left turns.

I have an update for everyone about where the coolant was going. I sent an engine oil sample to Blackstone Labs in Fort Wayne, and it tested positive for coolant. The good news is that the level of metals in the oil from bearing wear was low, so we caught the problem early. Now the question is whether the head is cracked or the head gasket is bad. (I suspect the cracked 0331 head.) I will keep you posted. Props to TJWalker and TruckD for their insights. The Blackstone Labs recommendation was particularly helpful! What a great company. -LFH

i just sent my own oil sample to blackstone labs for the same diagnosis....


at least you caught it early!

i have had this issue alot i found it to be the heater core and where it goes is in dash and on windshield or into truck. everytime early in the morning when its cold out i start truck and if its on deforest from the night befor i can smell it sweat smell for a second and then its gone sometimes u can take your fingure and feel the base of the windshield and notice a film! thats the coolant there

Update: The pressure test revealed that the 0331 head was indeed cracked. For the record, this crack happened without an overheat. The design flaw in the OEM 0331 head is frustrating, to say the least. I am ordering an aftermarket head with a 5 year, unlimited mileage warranty. I never want to have to do this repair again.

and people thought i was crazy when i said this when i first came on this site.

Well, it's time to bring some closure to this ordeal. The new aftermarket cylinder head is on, the Jeep is happy, and the pockets are empty! :-) The old cylinder head had a hairline crack between cylinders 3 and 4, just where the 0331's always fail. The crack was small enough that I couldn't see it with the naked eye and the pressure test was needed in order to find it. I hope they recycle that lump of iron and make it into something useful!
For those people searching the topic in the future, here's a summary of what happened:
- The jeep suddenly developed a slow coolant loss, about a quart ("full" down to "add") for every 300-400 miles.
- Careful inspection of the radiator, hoses, t-stat, water pump etc. showed no external leak.
- Oil level did not rise, as the coolant seeped very slowly into the oil and probably evaporated off.
- The Jeep never overheated, as I was careful to keep the coolant level above "add."
- An engine oil test by Blackstone Labs revealed coolant residue in the oil. Coolant in the oil will cause your oil not to work properly, so that your bearings wear out very quickly. I had gone about a month, or 3000 miles or so, since the coolant began to leak.
- I searched for a 2003-6 "TUPY" head, but not finding one I ordered an aftermarket cylinder head instead.
- After replacement, everything seems fine. Oil pressure is on the low side of normal, but still above 13 at hot idle, which is the minimum specified in the factory service manual.
K&J Tire in Jackson, MI, did the work and deserve lots of good karma. They have awesome customer service and did an excellent job.
Hope this thread helps someone save their 2000-2001 4.0 before catastrophe strikes! Cheers, - LFH

Just wondering if you have any news to report since you replaced your head. I fear that I might be headed down the same road and I'm torn between keeping the jeep or selling it so I don't have to worry about the cracked head.

I've put a decent amount of money into it (compressor, shocks, brakes, tires, water pump) since I got it in January so I'd like to get some value out of it, and I love the truck, but I'm thinking of just cutting my losses and selling it.

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Sorry for the month-late reply, grantman and Turbo! I only visit CherokeeForum intermittently now, since my Jeep actually got side-swiped into a cement barrier on I-76 back in April. For the record, she was totaled 10 days after getting the brand new cylinder head, and 6 months after a new rear suspension. The other driver left the scene, but at least we were ok. The good old XJ was made of solid American steel, and the airbags deployed as they should. Such a good vehicle! I will miss it. If Jeep still made them, I would have gotten another. I just couldn't justify buying a 10 year old vehicle (the 2001 being their newest year) with all the repairs I'd already invested. I now drive a 2008 Liberty. She's the boxy style like the XJ, which I like. The KK is a totally different creature from the XJ, though. Both have their good points, but the new KK has yet to cut her teeth on the trail. I hope she'll be as capable on those washed-out Forest Service roads as my old XJ was. And I hope the cylinder heads never crack! (it's a V-6) Cheers, --LFH