New issue, low to no oil pressure!

[JohnX]

From an economic standpoint, that doesn't make sense, but have fun.

 

[old_man]

If you are going to pull the pan to swap the oil pump, pull a couple of rod and main bearing caps and take a look at the bearings. Ideally, use some plastigage to see what the clearances are.

 

[RCP Phx]

From an economic standpoint, that doesn't make sense, but have fun.

The cost of build, no, but the info gained would be priceless!

I plan to replace the pump this weekend, that will give me a spare pump to evaluate!

 

[Ecomike]

If you are going to pull the pan to swap the oil pump, pull a couple of rod and main bearing caps and take a look at the bearings. Ideally, use some plastigage to see what the clearances are.

Can you pull and replace piston rings from just the bottom side?

 

[Overland]

Can you pull and replace piston rings from just the bottom side?

While I haven't had a 4.0 apart, most engines I've been into have wide main bearing bosses which would prohibit you from dropping a piston out of the bottom. You could pull the head, hone the suspect cylinders, and to an extent, go back with oversize rings on the original pistons without removing the crank, but it's messy and chances are it won't last that long.

On low speed engines, it ain't no thing.

 

[RCP Phx]

Can you pull and replace piston rings from just the bottom side?

No, but piston/rings/cylinders are not even in question at this time. I keep forgetting to drop a scope in there! The oil pump will hopefully buy me some time and help diagnose the real issue.

I am somewhat looking for a core motor if I determine this needs rebuilt.
But finding a 2000 isn't going to be easy!

 

[JohnX]

Is the 2000 block special? COP mounts on the head, but any other differences?

 

[old_man]

Can you pull and replace piston rings from just the bottom side?

You wouldn't want to do that anyway. If you are going to re-ring due to wear, you need to pull the head and use a ring land remover to take off the lip at the top of the cylinder, then hone the bore. It is normally not a good idea to just slap a new/oversized set of rings in an engine. I used to be done years ago if you were broke, but it really does not provide a long term solution.

If money is an issue, you can save a ton by pulling the engine and tearing it down and cleaning it before taking it to the machine shop yourself. But first, see if it is necessary. Measure the compression, wet/dry, pull the crank and rod bearings and do a visual along with plastigage check. It seems you have one idea stuck in your head and don't want to even diagnose the problem before throwing money at it.

 

[RCP Phx]

Is the 2000 block special? COP mounts on the head, but any other differences?

Not that I know of, the only difference is that it doesn't have a distributor.
The big issue would be the 0331 head, I'm unclear about Mopars website because they require a core?

 

[Overland]

I just bought a complete 01 which really only needed a rear end for $300 and they said the engine had been rebuilt two years prior. I drilled the head for the temp sensor, changed the alternator bracket, and put it in a 96 using its original manifolds. It was really easy to line up the indicator in the cam sensor and stab a distributor back in. The difference in head porting is minimal, and I can't tell any difference from the previous engine other than it's a lot quieter. I even left the motor mounts bolted to it.

It would be just as easy to go the other way, and there's brackets to fit the coil pack on an earlier head.

 

[Devilfrog]

The XJ blocks still used a distributor boss, but in 2000 the distributor was replaced with a Cam sensor.
Hell, my 2000 XJ has a stock block with a 98 casting number on it. I also suspect most 99 and up XJ blocks will show the same casting date as the 4.0 was redesigned in 99 for the TJ and WJ platforms. While the XJ retained the earlier legacy platform.
As for the COP issue, easy simple straps hung off the valve cover bolts solves that concern. Been done for years and well documented here. My own has had a strap hung COP since 2005 (hanging off a 93 cylinder head on my stock block).

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[RCP Phx]

Well I got the pump changed out(Melling HV). It did bring my pressures overall, but it's still different from the last 15yrs! I think this will buy me the time to sit back and plan a build! I plan to check the radiator today for "combustion leaks", I'm assuming now that I have a cracked head!

 

[Green Mesa XJ]

It hopefully gets you the time you need. I bought a junk yard 4.0 cheap to rebuild if i get time. Meant to do it already but life came up, I can see the compression getting weaker as I test it during maintenance.

Just a thought but you've got a new sender now so you may never see the same numbers


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[gradon]

That's what I said. Massive overheat of a 0331 head and then oil pressure loss sounds about right.


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[RCP Phx]

Well I'm chasing Ghost's right now. The Combustion gas check showed nothing, so I'm at a total loss as to what's going on?

 

[Green Mesa XJ]

Well I'm chasing Ghost's right now. The Combustion gas check showed nothing, so I'm at a total loss as to what's going on?

That combustion test only shows results in certain situations. Seeping leaks will not be caught.
Are you losing fluid?


Chasing phantoms you think you have is maddening. my Toyota engine is known for BHG, every minor indication I think it's gone. Why because I've owned a car with that motor since I was a teen and replaced several headgasket and rebuilt the knocking bottom end on several jap cut out motors.
The motor I have now is fine, good on all the tests, with a headgasket that should never blow, but it's in the back of my mind.


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[RCP Phx]

Yes, I've been losing/using coolant when this all started!

 

[Green Mesa XJ]

Yes, I've been losing/using coolant when this all started!

Ugh. that sucks.
If it is seeping it will just be enough to get in to the combustion chamber but not blow exhaust gas back into the radiator fluid. You could also have a heater core or something else leaking.

A leak down test would tell you if the motor is the cause and possibly where. Radiator pressure test might help too. It's a difficult call, I'd bet with the history of that cylinder head number (overheat and oil pressure) it is gone and plan on a rebuild. Just depends how much work diagnosing you are willing to put in. I'd hate to waste a perfectly good motor, on the other hand doing a ton of work diagnosing could be a waste of time.

I've just pulled motor I was sure the headgaskets would be seeping, take it apart to find the head gaskets were ok, it was the neglect of the previous owner not changing oil for 50k that killed it. Either way the motor had to come out, but I've had two modern motors I did a lot of work diagnosing to have to pull them any way.

 

[gradon]

The coolant seeps out of the cracked head into the valve train area and then drains down to the bottom end and then gets sloshed around and pumped back up and then destroys the bearings. Coolant loss and higher than normal oil level(if yours doesn't leak like most of ours), and maybe milkshake on oil fill cap are the norm. Combustion gasses in coolant will not be unless headgasket breach.


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[RCP Phx]

Been watching the oil constantly! I bought a new reservoir today along with a radiator cap and oil fill cap!

Shoot me if this was it, but I noticed that the reservoir hose was loose at the factory clamp !!! There was a trail down behind the bottle, never know!

If it was my new Griffin radiator, you'd could hear me screaming in Maine!!