Jeep Keeps Blowing Heads

Hello everyone. In the summer of 2016 I rescued a mint 1998 Jeep Cherokee barn find. It was mint... looked like brand new but the engine was toast. I replaced it with an engine from New York. It is another 4.0 from an XJ of the same year. Within 6 months the head cracked. I replaced it with a special one custom made locally. Another 6 months passed and that one cracked as well. So I did this most recent head swap with the Jeeps headlights on just to warm my hands while doing so.
When I did all of these jobs I replaced:
O rings on both sides of injectors
Head gasket
Valve cover gasket
Intake gasket
Head bolts
Lubed rods and rocker arms with assy lube
Used correct pattern and torque specs for head
Bled cooling system
195 thermostat
16lb rad cap

For those of you if any that have seen me on youtube know I have done much more than that. But as far as the basic head swap goes id just like to know... Did I have bad luck? Or am I doing something wrong here.
Just trying to make sure this Jeep doesnt eat coolant again especially since its my daily.

Ok, that’s weird. Just the original engine dying is odd, 4.0 can take a lot of abuse including overheating. Putting a thing cylinder head on a 4.0 seems excessive.

Was it overheating? I’m thinking if the original engine died do to similar circumstances maybe there something wrong with the cooling system or possibly the PCM not activating the cooling fan properly.

Far as cooling radiator, water pump, mechanical fan, water passages and freeze plugs in the block, clogged heater core, come to mind. If the original engine or replacements sat for years with radiator fluid inside the engine all kinds of buildup can occur.

Unless the block mating surface is badly warped I wouldn’t think it would be the problem.

Clogged catalytic converters can cause the engine to run hot. I’ve know of people who swapped the engine to quickly burn up the next one because the cat converter was clogged.

You seem to know what you’re doing mechanically so my guess would be with the history as described is you stepped in to a bad situation that killed the original engine without being able to see the clues to the causes. I could be wrong about this, and it’s not connected to anything and limited to the second engine/block.


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Crap can’t edit my last post,
I was trying to say going through three cylinder heads seem excessive.


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Here is a list of everything I put in the Jeep when I restored it the first time :rtm:
Radiator
high flow cat back (so yes the original cat is still there)
two injectors
injector o rings
cylinder head
power steering
water pump
alternator
air conditioning
head gasket
valve cover gasket
push rods
rocker arms
harmonic balancer
belt
high performance fuel pump
upper radiator hose
brakes all around
thermostat
full tune up and using the appropriate copper plugs they run best with
turned the fan by hand and it was stiff so the clutch is good
blower resistor
actual blower motor
headlights
tires
rims
swapped the ac compressor bracket because that bearing was not good and I didnt have the proper press to remove and install a replacement. So I just pulled an entire bracket with bearing
and finally painted the undercarriage
Im sure theres some other things but im failing to remember at this exact moment.

I feel that I did everything I should have done even as a college student with a part time job. I never noticed the needle pushing even one notch over 210 on the gauge. It usually floats just a slight hair below the 210 on the gauge. Although my heat is weak so flushing the core definitely did not get everything out water did flow through it.
The one thing that I could try is a high flow cat and manifold. Just may have to stop trying to figure out what all would go into a 3 inch lift kit because a good cat and exhaust manifold is not cheap. You would think the gauge would read something other than normal operational temp though if overheating is the problem. But every head I have put on is an 0630 so its not prone to cracking.

Oh yeah and intake gasket as well as replaced those pesky inverse torx bolts on the bell housing with regular bolts

With replacing the head so many times without ever touching the block is asking for a problem. Do you chase/clean the threads and use something like "Ultra-torque" on the threads? I would also suggest some ARP head bolts.

I used fel pro head bolts which I have never heard a bad thing about. I did make sure the threads were clean and did use the appropriate thread locker for the bolt that requires it. Assembly lube was used but not on the head bolts themselves. I am confident that they are torqued down to the appropriate spec.

Also I would like to specify that I had the original head tested at a machine shop and they told me it was cracked. The second head I would assume is the same story because two of the head bolts had rust on them. I did not get that head tested because shops overprice that simple task its ridiculous.

Here is a link to my youtube video showing the damage from the most recent head blowing incident. If you want to see what I found just jump around in the video and see the bolts I was talking about and the head itself. https://youtu.be/zTAmSDXdFek

Again my goal is to make sure this third one does not blow. It has been running well so far.

Have you check the deck of the block? Where the gasket and cylinderhead mate.


I agree ARP bolts and studs are great, I used them on some of the Toyota engines I build up, but they are pricy for a student’s budget.

When you get the jeep running again might want connect to the computer to see if the temperatures on the gauge is correct.



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Um, I’m going to guess cylinder three was where you had the problem before. I think the block was a warp there or the head does. I’m not even sure your current cylinder head is had. From what I saw the gasket didn’t blow. With those bolts like that I don’t think it was flat and the seal was made correctly.

Unless you see a crack I’d take that head and get it checked. I wouldn’t be surprised if it’s ok.



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Paul (Green Mesa) Thank you for the private message. The head you saw in that video was 6 months old. Was the second cylinder head I went through. It was custom made by a machine shop locally. I think they did a bad job on it or something but im here because two cracked heads in a two years seems like more than bad luck. I put the most recent head on a few months back and its running well as my daily. I had checked the block before applying the new head I ordered and it was strait and true. Im sure my tools are not as good as yours but they are pretty good. I did buy a thicker gasket just for safe measures. I have had the XJ running for a few months now with the new head and working well so far. There was another video on my channel about putting it all back together. I will have to find a way to access the temp from the computer to be sure its accurate but thank you for your help.

Something you mentioned earlier did get me thinking. You mentioned something about bad caddies causing problems like this? I could see bad o2's fouling up plugs. Or bad caddies causing a restriction and the engine running rough. But to fathom something like it causing a head to crack makes no sense to me. Have you experienced this yourself? I do have the original caddie on there so this is something im curious about.

My autocorrect may have changed a few words before I posted.
A clogged catalytic converter can cause overheating.
Running to lean can cause over heating too. Which O2 sensor change the mixture.


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I will plug in a scanner and see if I can access the temps to find out for sure. However im confident its running at proper temp. I think the torque converter rubs very, very slightly. And I do mean extremely slightly on the bell housing someplace so that could be generating some heat as well

I have heard recently of a possible rare block issue that lets coolant get to the threads of the second front bolt, drivers side, and that would use copper silicone sealant on both front bolts on the driver's side in the future. Rust on the bolts and coolants leaks into the exhaust manifold, that is never seen, is what happens if the threads on those two (or the one) front bolts are not sealed with sealant (not thread locker or lube, but copper silicone sealant) is not used.

Now onto the head issue, I would use an IR temp gauge to look for hot spots, on the head, block, etc.

You could have a bad connection to an injector making one cyl run lean enough to crack the head. A warped Block surface. But that would show up in periodic spark plug color, and fouling inspections!!!

Are you inspecting the spark plugs????

How do you know all the heads cracked if they were not inspected???

What happened that caused you to pull the head the last time???

Why have you not tested and replaced as needed a single sensor, like O2 sensors???? Or tested the Cat converters for excess back pressure???

Since you have not had a cooling leak, blown up radiator to report, ??? etc, I am wondering where the head crack was and what leaked to where??? and which head???

Either the bolt tension is failing somehow, or the Block is not 100% flat, or part of the head is running too lean.

Have you tested the fuel pressure, at idle and at say 3500 rpm??? And during acceleration????


I have never had a cracked head, or even heard of one on anything but 2001 heads that have the known defect

All plugs looked good and the same apart from plug in cylinder 3 which was wet. The head was pulled because of large amounts of white, sweet exhaust and a miss that appeared out of nowhere. I checked the flatness of the block it was strait and true. The only sensor that seemed to be not working properly was the o2 on the exhaust manifold so that is what I changed but the others seem to be working as they should. Checking for hotspots is a good idea I do have someone with one of those guns to check it with

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is that a crack in your cylinder wall i am seeing at 8:23 ?

alwayzAMC said:

is that a crack in your cylinder wall i am seeing at 8:23 ?

Click to expand...

I cleaned everything up with seafoam. That was just a mark from something. Coolant or whatever. No crack

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Here's a thought. The connector that connects to the o2 sensor got damaged while restoring the vehicle. Not the part of it where the pins connect or the wiring. Just the end of the plastic where it makes sure you don't put it in the wrong way. I had someone else look at this after I bought a new o2 to help make sure it was connected the right way. So it should be connected as it should. But if anyone has any wizardry as to how to be sure it's connected correctly next warm dry day ill take a look

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