Stumped - Low oil pressure

[er0080]

Im about ready to drive my new XJ off a frickin cliff!!

Let me begin by saying I have been reading the numerous threads regarding low oil pressure, and there seems to be a serious issue with 2000 - 2001 low milage 4.0L XJ's that should have been addressed by DC long ago. I cannot determine wheter or not these camplaints regarding the "oil pressure dropping to near zero at warm idle" issue are indeed all the result of bearing damage caused by subsequent coolant leakages into the crankcase from a cracked/defective 0331 head. Out of the 5 - 6 cases of this I have seen posted here, the original poster never followed up with a solution or a diagnosis at that. I would seriously like to put this issue to bed because I'm guesing there are several others out there like me who want an answer.

That said, let me say that I recently bought a 2000 4.0L XJ w/ just under 50k miles. Driving around the first week I noticed the check gauges indicator lighting up at a warm idle, only to find my oil pressure burried at zero! Cold startup builds about 45psi. First though was the oil itself. I changed the oil with 5w30 and put in a new puralator and the problem persisted, so I swapped the sender with the same results. Crosschecked new sender with my mechanical gage simultaniuosly and the results were identical. Now I knew I had some serious problems. Pulled the oil pan, inspected the oil pump cover for excesive clearance - looked like it had been replaced recently. The shaft also engaged properly with the cam gear. Replaced the entire pump anyway cause I got one cheap. I dropped the mains and rod bearings next. Main bottoms .001 undersize/tops std.size both with little to no wear. plastigaged them all at .0015" oil clearance. The rod bearings were a bit worn: tops .001/bot. std size - is this a factory practice? raplaced rod bearings for shats and giggles with .001top/.001bot. - plastigaged at .0015. While under the lift I noticed quite a bit of water in the oil dripping down from the block. Searched the forum then came across the 0331 cracked head posts. Sure enough, between 3 and 4 exhaust ports was a gaping crack leaking coolant! wow what crap all in the first week of ownership!

So I replaced the head with a reman 0331 cast (why i chose to go with another 0331, I dont know!) Ironicly I noticed it was welded/reground in the exact same spot my old one had cracked! I was a bit hesitant about putting the new one back in, but the one year warantee gave me a bit of confidence....

Sunday I finished up and fired it up with no problems. Purred like a pussycat! Ran it at idle for 20 minutes then took it for a spin. Would you believe I have the exact same pressure problems - ~0 pounds at idle, <20 at 1600rpm with awful lifter noise - like as if i didn't "fix" a damn thing! Rechecked the new head for the crack and it looked like it was holding. I drove it it all sunday then today, dumped the oil and didnt detect any water but oil seemed a bit thin. Replaced oil with 20w50 and same thing! I haven't overheated it since I've had it, with coolant temps never exceeding ~205F.

So now my dilemma...where is the pressure (or should I say oil) going? severely worn cam bearings? Cracked block? What about the lifters? When I had the head off, I pulled all the lifters, inspected, cleaned and reprimed them. All were slightly worn (crown on camshaft mating surface were CONCAVE to about .001" - seen lifters much worse! I'm confident I did the bearings right because ive done probably 10 of these jobs before, although performed on engines removed from the vehicle. You would think pressure decreasing with coolant temp would be indicative of bad bearings - I'm at a complete loss.

Please, help me with your experiences. I am seriuously considering a complete rebuild at this point! Any info would just be great. BTW, i bought this vehicle at an auction with the assistance of a dealer friend who passed his wholesale savings on to me, so I can't really hold him resposible for repair costs. Well, i guess I could at the expense of the loss of a friend!

Thnks,
Eric from upstate NY

ps - things i havent done but I am considering:

compression test, but I have *plenty* of power
leakdown
coolant pressure loss
pulled the motor - next?

 

[Dr. Dyno]

You've confirmed one thing that I already knew; that the 0331 heads are junk. It's time for everyone who's had this problem to take a class action suit against DC to get this problem solved. The same problem seems to be endemic here in Saudi Arabia as well so we are not talking about one or two isolated cases.
I think the only solution to your low oil pressure problem is to tear down the engine again. I suspect that the cam bearings are worn in which case, you'll need to have new ones pressed into the block. Since you'll be rebuilding the engine anyway, you could consider converting it into a stroker.
I strongly advise that you ditch your 0331 head and replace it with a 7120 ('91-'95) or 0630 ('96-'98) head. It'll be an opportunity to do a port job on it to gain a few ponies.

 

[Creighton]

You have basically wrote every issue i've had since I bought my 2000 XJ. I bought it and w/in a week of purchase (bone stock) I noticed the lifters making a lot more noise than I was used to. (I've been a import guy my whole life) and I took it to the dealership and they said "Its a straight 6, they make racket. But its nothing out of the ordinary for the 4.0". My oil pressure drops off exactly as you say... i'm having the oil pump replaced as I type... last week I had the dealership do a leak down test and compression check and the numbers were good across the board. They told me the oil pump was failing... so i'll let you know if that solves my issue.

 

[RichP]

This oil pump failing business has me nervous, anybody know when they changed to the aluminum pump ?

 

[Creighton]

Just drove the jeep around w/ the new oil pump and its still doing the same thing. I'll be replacing the sender unit tonight as well just for shits and giggles even though I'm sure it won't be fixing the problem. Just want to eliminate one more variable.

I always have the worst luck with cars... won't be purchasing a used vehicle ever again. Soon as I get rid of this credit card debt I think i'm gonna scoop a jasper.

 

[er0080]

thanks for the replies guys. Creighton - sorry to hear you are having problems. Before you change to sender, I'd strongly recommend going to home depot and buying a cheap water pressure gage and swapping it in where the sender fits. They carry one that has a standard thread which you can easily screw in temporarily. Although I now have a "professional" grade oil presure tester, I have found that for $8 you can use the water gage with exactly the same results w/o the cost, provided it can handle up to ~100 psi. I garantee you will find that your sender is fine. Did you mention if your cylinder head was cracked? Pull your oil filler cap and shine a flashlite down in there, you will easily see the crack leaking coolant if the crack is there.

Dyno - thanks for the advice. I dont have the extra cash right now to build a stroker, so the engine will probably remain stock at this point. Those cam bearings mut be toast for 20w50 to idle at 5psi!!!! I wonder if there's a crack in the crankcase somewhere causing an internal oil leakage? At this point, I wouldn't be surprised. I just hope I haven't overlooked something blatantly obvious...

Eric

 

[MAP]

Way back about 10 years ago, my dad helped me rebuild my first pushrod engine on an old econo front wheel drive Chevy(guess what it was).
Anyway, we put the thing together, turn it on and notice it has very low oil pressure. We took off the oil pan and check all the bearings and oil pump..everything looked OK.

After replacing the oil pump, bearings and closing it up again, the problem persisted. Finally we pulled the engine and disassembled it.
Guess what, the guys at the machine shop that installed the cam bearings didn't install one very well. He didn't push the bearing in all the way such that the oil channel under the bearing was exposed... all the oil was escaping through there. We were pissed..

My dad has rebuilt several engine since then and that's the first thing he looks at when he gets an engine back from a machine shop.

MAP

 

[Creighton]

er0080: I took the valve cover off and looked in and I did not notice any cracks anywhere? Is the crack to the left or right ony our head? I'm so confused and iritated at this point I don't know what to try other than paying someone to completely rebuild the motor... but at that cost I don't know if it would be justifyable to just get a whole new motor.

 

[RichP]

I wonder if the bypass could be fubared up.....

 

[Creighton]

I wonder if the bypass could be fubared up.....

Do you mean the bypass valve?

 

[RichP]

Do you mean the bypass valve?

Yes, I have to wonder if it is stuck open ? I've not looked at one real close but the ones I have looked at have a reducer of some sort. I'm just trying to come up with ideas before you tear into the block to get at the cam and those bearings.

 

[Creighton]

Hmmm. I'll mention that to my mechanic for sure, thanks for the input. Whatever it is, I can notice it getting worse and worse as the days go by. It used to take a few seconds for the pressure to fall off now its just dumping to 0 psi almost instantly. AND when I am driving under normal conditions (about 50mph and 1.8k rpms) I used to sit about 20-25 psi now its right at 15psi. And never gets above 30psi.

 

[Creighton]

also a tid bit.. if it were mains and such wouldn't the motor idle extremely rough and make some good amount of racket? I just did a quick test.. let it run at 0psi for about 5 minutes just to see how the motor reacted and all it did was go up in temp from 215 to maybe 218 or 19 or so. Ran just fine.. no hesitation or knocking or abnormal sounds.

 

[RichP]

Hmmm. I'll mention that to my mechanic for sure, thanks for the input. Whatever it is, I can notice it getting worse and worse as the days go by. It used to take a few seconds for the pressure to fall off now its just dumping to 0 psi almost instantly. AND when I am driving under normal conditions (about 50mph and 1.8k rpms) I used to sit about 20-25 psi now its right at 15psi. And never gets above 30psi.

The other thing that just came to mind, could there be a restriction in that oil filter mounting setup. It is possible that there is some stuck in there and blocking flow, easy enough to remove the one bolt holding it in and take a look see...could be some crud broke loose and was pushed thru the pump into that area and never made it to the filter and got lodged in there...

 

[Creighton]

ALSO! Another bit of trivia to my similar symptoms was I bought the vehicle and it ran fine for 3k miles w/ no problems. I changed the oil over to synthetic (93k Miles) and thats when I started having all the oil pressure problems...

 

[RichP]

The synthetic would have started breaking down any sludge in there after a couple hundred miles. Could be that mounting system where the filter is needs to be cleaned out. One bolt to check it and run a brass brush thru the passages and a new set of O rings..
I had shot mains on my 82 S-10, other than low oil pressure it ran fine, no noise or other notable noises or issues, that engine had over 680,000mi on it.

 

[er0080]

any restriction in flow would certainly cause a pressure *increase*, assuming the pump is doing its job, which i'm fairly certain it is. Furthermore, if the bypass valve were stuck open, this would actually help the situation because the pressure drop associated with the flow through the oil filter would be then be negated. Basic fluid mechanics, really. That being said, I have already removed and inspected every part of the oil system from the filter down to the pickup. I would not recommend tearing into the filter housing if you have these pressure symtoms.


Eric

 

[er0080]

creighton, If you have the valve cover off, the crack should be quite easy to see if it is in fact there. Look along the base of the number 4 exhaust port rocker arm boss. You should see a fine crack crusted over w/coolant. One other thing I noticed - don't wipe off the head near the crack because the crack is much easier to detect with coolant in it. When I wiped mine with a rag the crack all but disappeared unless I stuck my face right in there for a close look!

 

[Creighton]

creighton, If you have the valve cover off, the crack should be quite easy to see if it is in fact there. Look along the base of the number 4 exhaust port rocker arm boss. You should see a fine crack crusted over w/coolant. One other thing I noticed - don't wipe off the head near the crack because the crack is much easier to detect with coolant in it. When I wiped mine with a rag the crack all but disappeared unless I stuck my face right in there for a close look!

ya, i looked around inside there when i had it off at the time (the dealership i bought it from had basically no RTV on and it was leaking.) and i didnt notice any coolant lines or drips or cracks.. but i coulda missed something, who knows.

 

[er0080]

well it just so happens that the crack occurs directly under the oil filler cap, so to see if its there, you don't even have to remove the valve cover. Just remove the cap and shine a flashlite down there.