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Unread 12-19-2012, 10:55 AM   #1
Submariner
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I6 Head Problems on 1999 to 2001

I heard that cherokee's had problems with the I6 heads? something about they warped and were not that reliable.

Does the TJ's have the same problem with the I 6 engine?

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Unread 12-19-2012, 11:14 AM   #2
prjohnson
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Yes

They Crack. The 0331 heads crack on early TJ's. I think the main ones were 2000-2001. IDK for sure...If you search, you'll find more information.
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Unread 12-19-2012, 11:22 AM   #3
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yup.

the issue is around all 1999-2001 4.0L's that used 0331 non-TUPY revision heads. that's XJs, WJ's and TJ's.

The company that made the heads for Jeep didn't use enough nickel in the iron casting, so the metal turned out to have ductility problems.

The head usually starts cracking around cylinder 3-4 area, and you can't tell if its cracked unless you pull the valve cover off. If you think about it, as the head heats up during combustion, then cools down when you park it outside at -20F, the metal expands and contracts. You do this thousands of times over a few decades and you've got a whole bunch of expand/contract cycles. That's the cycling that causes a head that isn't ductile enough to crack.

TUPY revision heads fix the issue. If you crawl on top of the motor, take the fill cap off the valve cover, and look directly down with a flashlight, you want to see "TUPY" cast in the cylinder head. If it's a 00-01 TJ and it doesn't have that marking, it's a "bad" 0331 head.

It's also worth noting not all non-TUPY 0331 heads crack. Some are just fine, some a ticking time bomb. it all depends on the thickness of the casting in the problem areas...and theres really know way to test it...so it's just best to avoid the potential issue.
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Unread 12-21-2012, 08:59 AM   #4
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I had the same problem on my 99 TJ but it was not the 0331 head. But the problem was just as unlimited04 describes.
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Unread 12-21-2012, 09:13 AM   #5
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Any idea when in '99 they started with the bad head? Curious, as mine is an early '99 I believe.
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Unread 12-21-2012, 09:17 AM   #6
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Scratch that...my build date in Chrysler's computer is April 15th 1999. Crap!
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Unread 12-22-2012, 08:48 AM   #7
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My 2001 cylinder head cracked after about 8 years/100,000 miles. Now I have an aftermarket head (and new motor) and won't worry about it anymore.
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Unread 12-22-2012, 09:01 AM   #8
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OK I am looking for a "OH Sit" a 1997 to 2002 TJ.

How do I know if the head is cracked? What would be a good indication taht it is cracked?

White smoke out of the tail pipe! running rough!

or is there something else that is a telltale on it?
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Unread 12-22-2012, 09:08 AM   #9
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Quote:
Originally Posted by Submariner View Post
OK I am looking for a "OH Sit" a 1997 to 2002 TJ.

How do I know if the head is cracked? What would be a good indication taht it is cracked?

White smoke out of the tail pipe! running rough!

or is there something else that is a telltale on it?
as said earlier, you need to take the valve cover off.







http://www.jeepforum.com/forum/f11/0...advice-347035/
http://www.jeepsunlimited.com/forums...d.php?t=391831
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Unread 12-22-2012, 06:31 PM   #10
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Hmm, well, I have a 98 but they all run rough after a certain amount of time.
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Unread 12-22-2012, 09:08 PM   #11
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Or to avoid pulling the valve cover, just remove the oil cap and shine a flashlight down in it and look. The only good thing about the weak spot is it can be seen from the cap.

The head just cracked on my sons Cherokee about 2 weeks ago. I had checked it a few times in the past and it was fine but after driving it and it got a little hot on me that day I pulled the cap as it was running and could see water bubbling from the crack as the engine was running.
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Unread 12-22-2012, 10:46 PM   #12
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Quote:
Originally Posted by Submariner View Post
I heard that cherokee's had problems with the I6 heads? something about they warped and were not that reliable.

Does the TJ's have the same problem with the I 6 engine?
The #0331 head did have a slight tendency to crack sometime around 130-180Kmiles. This is the "early" head, through mid-2001 - the later head with the "TUPY" foundry mark is revised to correct this.

The crack, if it happens, can be seen merely by removing the oil fill cap and looking in - it usually cracked on the upper surface, between the #3 and #4 cylinders. I am not informed as to how well stop-drilling and welding works.

The "TUPY" mark may be found in the same location, it will be raised from the surface of the head.

The cylinder head casting ID number can be found outside the valve cover, top surface of the head, above and between the #3 and #4 exhaust ports.

The TUPY 0331 head is a direct replacement for the earlier 0331 head. Also, the 0630 and 7120 may be adapted to fit - the intake ports did not move or change very much, but the exhaust ports did reduce in size with each change. An adapter plate would be needed - use min. 1/8" thick steel (mild steel okeh,) and two exhaust gaskets - the one correct for the head goes on the head side, the one correct for the manifold on the manifold side. Open up the plate with ports matching the later gasket with the smaller ports. Use screws 1/4" longer, get flat washers to take up the difference (retain and reuse the bowl-shaped washers directly against the manifold flanges, or replace those with true Belleville spring washers - they're there for a reason!)

The reason for this is the reduction in port size - you can actually end up seeing inside the port if you put the later exhaust on the earlier head, as the primaries won't fully cover the port.
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Unread 12-22-2012, 10:53 PM   #13
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Quote:
Originally Posted by Submariner View Post
How do I know if the head is cracked? What would be a good indication that it is cracked?

White smoke out of the tail pipe! running rough!

or is there something else that is a telltale on it?
On my jeep, the exhaust was fine. When the heads crack on the 4.0s, the coolant doesn't get into the combustion chamber, so you won't see any changes in the exhaust.

The symptoms for mine were:

1. Mysteriously vanishing coolant.
2. Milky-looking oil under the valve cover and on the underside of the oil fill cap.
3. Low oil pressure
4. Clacking noises that I assume were coming from the lifters. Also, I assume the bearings in my motor were shot due to all the coolant mixing with the oil and the low oil pressure.

Here's what my leak looked like. If you look closely, the crack resembles an upside down "U".

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Unread 12-24-2012, 09:09 AM   #14
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OK, If I find a TJ with this crack in the head, what does it cost to replace it? Lets say that I replace the head myself. and then I have a dealer fix it. I am looking for negotiations on a bad TJ.....in case I find one.

and how long do you have before you really need to replace the head once it goes south.
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Unread 12-24-2012, 09:55 AM   #15
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You CAN wait, but its not recommended, change it as soon as possible because coolant and engine oil is a bad combo
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