Little to NO Oil Pressure

Hey guys, well my "trusty" 4.0 has developed what I think is a terminal illness.

About two weeks ago I was driving along, came to a stop light and noticed that my "check gauges" light was on. Some investigation has led to the discovery that at idle, my Jeep only has 5psi of oil pressure. Reved up to about 2K I am only running about 13psi. When the engine is cold, right after cranking it runs about 40psi, but as it warms up to 210 the oil pressure drops to the above figures.

This is what I have done thus far:
-tested the oil pressure with a manual gauge to rule out the sending unit
-replaced the oil pump
-changed the oil with a new filter (10w-30)
-new water pump and thermostat, along with radiator flush and new fluid at an attempt to lower the engine temp

While I had the oil pump out a quick glance up into the engine didnt reveal anything out of the ordinary, but I wasnt really looking very carefully.

I took it to a mechanic, who told me it was the sending unit until i told him to test it with a manual gauge, then he told me that it was something in the "crank" and that my best bet was to drive the engine until it blew and then to get a new engine.

Any ideas? At idle, when the engine is at its lowest oil pressure I do not get any bad engine noises, nothing sounds like it isnt getting lubed. I bought the jeep used with 60K on it and since I have owned it I changed the oil regularly. Any ways to increase the pressure a few PSI? One mechanic told me to try 20w-50 oil and the Jeep place told me 10w-30.

I searched and did not see anyone with this same problem. One of the mechanics that checked it out told me this was a first for him, 5psi and no noise.

I would pull the pan and plastigage the crank and journals to see if they are toast. If the crank is good but the bearings are getting worn, I would probably just put in a new set of bearings. This used to be a very common practice, but it didn't make as much $$$ for the mechanic, so the practice has pretty much gone away.

This is all getting alittle over my head probably.

At first I didnt know what a plastigauge was, but I pulled out the trusty haynes manual and did some research.

My question is, if it is my bearings...are there any specific gaps or over size or undersize bearings that i need? Or would that also all be determined by the plastigauge?


(and yes i have a more experienced friend that can help me out with this stuff, i just want to expand my knowledge)
thanks,
Aaron

First question, what brand oil filter ? I had Purolator Pure ones do that on my 2.5L TJ...almost gave me heart failure. Replaced it with a mobil-1 and pressure was back.
Now comes the interesting part, the TJ only gets used a couple times a week, I noticed the other day that the pressure was low at idle first thing in the morning, drove it for about 20 miles to the barber, it sat parked for about an hour as I waited my turn. When I got back in an drove home the pressure at idle was 20psi, it has done this a couple of times but has not dropped to -0- like it did with the purolator. The only difference was on the ride home I turned the key on and then plugged in the cell phone charger to charge up my blue tooth headset, made sure it was charging and then started the engine.
Someone here mentioned that if they put the key on and wait 20 seconds or so till the self testing is done THEN start the engine their engine runs better, so I tried it, pressure went to 60psi, warmed up and dropped to 20 at idle and would not go below 20 even after a 30 mile ride to a customer site, at 3k it stayed at around 50psi. On the ride home after being there for 5 hours I fired it right up and pressure went to 40 and would drop to 10.
I'm wondering if I am seeing the beginning of connector corrosion problems and increasing resistance in the harness at 9 and almost10 years old in the TJ.
To my way of thinkig if it was worn bearings or pump it would do it all the time, I wonder if the waiting lets the system reset to some kind of baseline during it's post before it actually starts getting live signals from the senders and sensors.

Probably just the gauge sender if you aren't getting any noises.

I will try that but i do not think it will make a difference.

If it is the bearings, wouldnt the colder oil possibly create more pressure than the oil that is heated up?? And once the oil is heated, it does this ALL of the time.

This Engine has 90K miles. Oh, and I had a fram oil filter, and once the problem started my original thought was the oil levels and filter (I have a real mail seal leak also). So i changed them, to Mobil 1 Synthetic and a Mobil 1 filter...with no changes.

Thanks though

RichP said:

First question, what brand oil filter ? I had Purolator Pure ones do that on my 2.5L TJ...almost gave me heart failure. Replaced it with a mobil-1 and pressure was back.
Now comes the interesting part, the TJ only gets used a couple times a week, I noticed the other day that the pressure was low at idle first thing in the morning, drove it for about 20 miles to the barber, it sat parked for about an hour as I waited my turn. When I got back in an drove home the pressure at idle was 20psi, it has done this a couple of times but has not dropped to -0- like it did with the purolator. The only difference was on the ride home I turned the key on and then plugged in the cell phone charger to charge up my blue tooth headset, made sure it was charging and then started the engine.
Someone here mentioned that if they put the key on and wait 20 seconds or so till the self testing is done THEN start the engine their engine runs better, so I tried it, pressure went to 60psi, warmed up and dropped to 20 at idle and would not go below 20 even after a 30 mile ride to a customer site, at 3k it stayed at around 50psi. On the ride home after being there for 5 hours I fired it right up and pressure went to 40 and would drop to 10.
I'm wondering if I am seeing the beginning of connector corrosion problems and increasing resistance in the harness at 9 and almost10 years old in the TJ.
To my way of thinkig if it was worn bearings or pump it would do it all the time, I wonder if the waiting lets the system reset to some kind of baseline during it's post before it actually starts getting live signals from the senders and sensors.

Click to expand...

Good thought on replacing the Fram. I heard a few negative stories w/ Fram.

That is what the guy at the Jeep dealership said...but i dont think he really looked into my problem.
I said:
"This is what I have done thus far:
-tested the oil pressure with a manual gauge to rule out the sending unit"

I think that it is something internal...but it doesnt make much sense to me because the engine isnt making any bad im going to blow up noises.
I took the gauge sender off and put a manual gauge on there. I know that most people's problems is the sender, but i am not that lucky.

thanks though

Blaine B. said:

Probably just the gauge sender if you aren't getting any noises.

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Ok, was the manual gauge saying the same as the cluster?

what year is it?

Sorry, yes the manual gauge was saying the same as the cluster. 6PSI at idle and about 13 at 2K RPM

Sorry, it is a 2000, 4.0, auto

If i remember the diagram correctly, wouldnt the manual gauge be measuring the oil pressure pretty much straight from the pump. Could possibly the connecting rod that is supposed to turn the pump not turning it effectively?

JeepinAaron said:

Sorry, it is a 2000, 4.0, auto

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It's probably sender failure; seems to be semi-common on later XJs. Mine does this from time to time as well as pegging the needle at 80psi - and in the absence of oil spraying everywhere, the sounds of the vehicle disintegrating its engine internals, or chunks of metal in the oil at changes, I'm pretty much ignoring it for now.

FWIW, both my current 2000 and past 2001 liked to have the pressure sender fail after water crossings or heavy rains, showing 0psi.

I'd be concerned given what the manual gauge is showing, though. Idle's usually in the 20-25psi range, with 40-50psi normal when running. Did he check with the manual gauge under real-world running, or was he just operating the throttle to get the readings while sitting still?

JeepinAaron said:

Sorry, it is a 2000, 4.0, auto

Click to expand...

ahhhh ha. SOME of the 2000's and 2001's seem to have an issue with the heads cracking and letting coolant mix in with the oil,....ESPECIALLY if the engine has overheated in the past, and one of the first signs is crap for oil pressure.

It's looking to be somewhat hit and miss as to if you got a bad head or not....it only affects the 0331 castings (which began in all 2000 variations of the 4.0 (i.e. XJ, TJ, WJ)). However i'm beginning to think along the same lines as casm, and that it was just a "bad batch" of 0331's, and they're not all doomed to crack.

I don't recall this issue making any unusual engine noises...and I could be wrong there, but like I said one sure sign is significant drop in oil pressure, along with loss of coolant. Take the oil cap off and shine a flash light down in there and you should be able to see the crack, if there is one....they like to crack right there below the oil cap. Another sign is your oil will begin to look real creamy, or like a chocolate milkshake

Search on here for "0331" or "Cracked Head" or something like that and you'll see a lifetime supply of threads to further your knowledge.

Again this may not be the case for you, but the fact that it appears that you're sender is working properly, and you're still getting crap for oil pressure, this was the first thing that came to my mind.

Oh, and where in NC are you?

99XJSPORT06 said:

It's looking to be somewhat hit and miss as to if you got a bad head or not....it only affects the 0331 castings (which began in all 2000 variations of the 4.0 (i.e. XJ, TJ, WJ)). However i'm beginning to think along the same lines as casm, and that it was just a "bad batch" of 0331's, and they're not all doomed to crack.

Click to expand...

And on that note, a quick digression:

A friend of mine has a '99 WJ with the 4.0. AFAIK, this was the first year and vehicle to have the distributorless 4.0 - which means there's a strong possibility of it having 0331 heads. That thing has to have close to if not actually over 200,000 miles on it by now and I know he's needed ZERO work on it other than regular maintenance and a blown A/C compressor. In any event, next time I see him I'll try to get a look at the casting number and see if this is indeed the case; if so, it'd lend some more credence to the 'bad batch' theory.

Back to the regularly-scheduled thread

Ok this is something to check. I looked in the oil fill and didnt see any cracks. I suppose that step 2 would be to remove the valve cover and check. I'll try and do that tomorrow or something.

I am still interested in what people thinks about the bearings.

-Aaron

99XJSPORT06 said:

ahhhh ha. SOME of the 2000's and 2001's seem to have an issue with the heads cracking and letting coolant mix in with the oil,....ESPECIALLY if the engine has overheated in the past, and one of the first signs is crap for oil pressure.

It's looking to be somewhat hit and miss as to if you got a bad head or not....it only affects the 0331 castings (which began in all 2000 variations of the 4.0 (i.e. XJ, TJ, WJ)). However i'm beginning to think along the same lines as casm, and that it was just a "bad batch" of 0331's, and they're not all doomed to crack.

I don't recall this issue making any unusual engine noises...and I could be wrong there, but like I said one sure sign is significant drop in oil pressure, along with loss of coolant. Take the oil cap off and shine a flash light down in there and you should be able to see the crack, if there is one....they like to crack right there below the oil cap. Another sign is your oil will begin to look real creamy, or like a chocolate milkshake

Search on here for "0331" or "Cracked Head" or something like that and you'll see a lifetime supply of threads to further your knowledge.

Again this may not be the case for you, but the fact that it appears that you're sender is working properly, and you're still getting crap for oil pressure, this was the first thing that came to my mind.

Oh, and where in NC are you?

Click to expand...

I have a 2001 that I had to put a head on,had 0331 casting head.Had 62,000 miles on it when I lost oil pressure,changed sending units, oil filters, even changed oil pump to no avail.Found head cracked on the top surface between #3&#4exhuast valves.Pull valve cover and look for coolant leaking in that area. GOOD LUCK! DAVID

SlimsXJ said:

I have a 2001 that I had to put a head on,had 0331 casting head.Had 62,000 miles on it when I lost oil pressure,changed sending units, oil filters, even changed oil pump to no avail.Found head cracked on the top surface between #3&#4exhuast valves.Pull valve cover and look for coolant leaking in that area. GOOD LUCK! DAVID

Click to expand...

Thats what i was referring to.

Interesting you had to pull your valve cover off to see it. I've seen a couple with cracked heads and I was able to see it by just taking the oil cap off, and many others on here have said the same.

Cool thanks. I'll check on it tomorrow.

-Aaron

SlimsXJ said:

I have a 2001 that I had to put a head on,had 0331 casting head.Had 62,000 miles on it when I lost oil pressure,changed sending units, oil filters, even changed oil pump to no avail.Found head cracked on the top surface between #3&#4exhuast valves.Pull valve cover and look for coolant leaking in that area. GOOD LUCK! DAVID

Click to expand...

Forgot to mention, The reason for low or no oil pressure is the coolant that gets into the oil pretty much takes out the crank and other bearings !My crank had to be turned and polished,new cam and bearings,everything is new but pistons and rods!

Sorry to butt in guys,
I was wondering where on the head is the #'s 0331 found. I have the 2000 4.0 distributorless eng. I took that 2" round cap off to see what might happen when I was going to steam clean the eng. Wanted to know if I was going to create a condensation problem like the dist caps give when steam cleaned.
It looked similar to a pickup coil inside.
I replaced the cap and as a precaution, I wrapped a plastic baggie over it and fastened it with a zip tie and headed for the car wash.
I always let the instrument lights go out and buzzers stop before I crank the engine.
It started fine but 1/4 mi down the road, it stuttered a bit then went on with no more stuttering.
The little 2" cap had a bunch of wires to it, and I DID NOT turn it upside down to see what it looked like inside. But I think I like that setup better than the dist, cap and spark plug wires. No incidents after the steam and pressure wash.
After reading this thread, I'm really curious to know if I have the 0331 head, because I'm trying to find that elusive oil leak that drips slightly on my garage floor. NO water in the oil YET!