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KJ question sorry.

Something is off. Those 3.7 are do not like getting too hot so head gaskets can be common (like every aluminum head engine). I’ve heard about those engines dropping a valves but I’m not sure how common or what the cause is. I think it was more common 2002-2004 but don’t know for sure.

My guess is the head the put back on was not from that under 100k motor, they probably either farmed the job out locally for a rebuild and that local machine swapped it for one already the shelf or got a national rebuild company’s garbage head off a very abused motor. Other than that the damage to that head makes no sense unless the rebuild was out of spec and the damages followed.

Injectors can cause misses with no CEL, upto a outright fail the computer ignores it if it’s more mechanical and the injector is electronically responding correctly. Coil packs can cause issues I believe that design is three coil packs with a spark plug wire going to the other sides cylinder. Anything but mopar coil packs are prone to early failure.

I’d pull compression on that motor just to see what the hells going on. BTW that motor likes to be high compression.


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All the work was done by a very old established motor rebuilder (with a not so good reputation in the old days). They replaced the Cam with a used one. They did NOT swap heads, they just cleaned/serviced the valves only on the heads (My guess is that means they cleaned it and replaced the valve stem seals). They said nothing about resurfacing the heads or block, but in answer to my questions he said the heads themselves were fine, no cracks. My son had the jeep all over the country last year, 10 months many miles with only one part replaced, the oil pressure sender went bad, and one coil pack replaced to solve a specific cyl miss fire code, that was done about 2-3 months before the head gasket failed. It was leaking/loosing coolant very slowly about 8 weeks before the head gasket job. Lost maybe 2 gallons of 50/50 blend in weeks, about 2000 miles. He also replaced 5 spark plugs when he replaced the coil pack. Could not access the 6th spark plug.

The motor shop guy told me all 6 cylinders have 155 psig compression.

I did not realize the Liberty engine was over head Cam. Until last night when I went to the shop with my son to pick up, I had been told they were replacing the crank shaft, :laugh2: LOLOL. So at least I now have that part of the story straight from the horses mouth LOL.

But now I am wondering how you bend a steel valve stem, in an aluminum head, with out damaging the head???? And the piston???



Something is off. Those 3.7 are do not like getting too hot so head gaskets can be common (like every aluminum head engine). I’ve heard about those engines dropping a valves but I’m not sure how common or what the cause is. I think it was more common 2002-2004 but don’t know for sure.

My guess is the head they put back on was not from that under 100k motor, they probably either farmed the job out locally for a rebuild and that local machine swapped it for one already the shelf or got a national rebuild company’s garbage head off a very abused motor. Other than that the damage to that head makes no sense unless the rebuild was out of spec and the damages followed.

Injectors can cause misses with no CEL, upto a outright fail the computer ignores it if it’s more mechanical and the injector is electronically responding correctly. Coil packs can cause issues I believe that design is three coil packs with a spark plug wire going to the other sides cylinder. Anything but mopar coil packs are prone to early failure.

I’d pull compression on that motor just to see what the hells going on. BTW that motor likes to be high compression.


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That’s fairly low compression, for a 3.7 Spec is 170-225. my 2006 3.7 gunked to death by the previous owner had cold compression of 165-175 with like 150k miles on it. Actually that engine was ok except for the gunk, it got to the pan and pickup tube. Swaped it out anyway with a low milage 2012, to get the pan off in the vehicle was half the job of removing it, figured we were better off grabbing a low milage JY engine.

3.7 is not a bad motor over all, but because it has aluminum heads it’s prone to failures the 4.0 never had.

How did the headgasket fail and not warp the aluminum? I’ve done jobs on cars where I know they never reached operating temperature let alone overheating and the head was not warped, that was because the material Toyota use for headgasket was the weak link, as I recall the 3.7 is a metal gasket. I’m curious how the gasket went bad if it didn’t overheat. If it did overheat I’d think there should be warping.
The timing chain shouldn’t have much stretching at that milage and tensioner shouldn’t have failed either.
Dunno something seems off about the repairs being done.

The miss could be whatever brand coil pack was used, the cheap Chinese packs tend to fail. Or spark plugs/ old spark plug, it’s another jeep that doesn’t like anything but oem plugs. I think they are 35-45k replacement schedule. Getting to the spark plugs on the Commander isn’t tough, but we have 6 coils, maybe they had more room to get the coil pack out.


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I've had head gaskets fail and not cause issues with the head/block.
The issue was over pressuring of the cooling system, quite common on early 70's Renaults due to a sticking release valve.

In the locally remaned head dept, I've had valve jobs done by supposedly experienced machinists that came back with the valve stems looking like crooked teeth with their acceptable tolerance being +/- 1/8" at the stem.
 
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