How bad is this likely to be? Engine oil situation

[Anak]

Vehicle in question is the '97 ZJ I picked up a month ago. I know there is a ZJ section, but no one goes there, and this is the 4.0L engine. I expect I will get better answers here.


Once I got this thing to the point I could drive it some distance (10 mile round trip) I discovered that once properly warmed up the oil pressure gauge reads "0" at idle. It picks up to maybe 10 or 15 when driving. Very low in my book.


Among other things, I have just done an oil change on the vehicle. I can't believe how small of a filter this thing was running. I thought maybe Jeep had changed the filter adapter for ZJs and picked up a filter from Napa. I now see I could run the same filters I usually run on my XJ. Here is the filter the ZJ came with, what Napa sells for it, and what I would ordinarily run:

Since oil pressure was bad I decided to cut into the old filter and see what I could find. Holy cow. Not much that looks like shiny metal, but what a bunch of sludge:

I couldn't believe how bad that was so I cut open some other filters I had sitting around waiting for me to deal with them. No XJ filters on hand, but the worst I have is the one from my Cummins (evil mechanical coal rolling gross polluter). Nowhere near as bad as what came off this ZJ:

For those who have more experience with these engines, what is going on with this ZJ?


The vehicle came with an oil change sticker on the windshield. Next service date of 12/8/19 (overdue on time) at 174917 miles (current mileage is 172839, so still short on miles). "Last oil used 1030" I assume means they put in 10w30.


Along with changing the oil I put in a replacement sending unit (Napa) and added in a "T" so that I can hook up a real gauge. Will be interesting to see what I find next time I take this for a drive, but it isn't looking good for the engine. Bummer, because the chassis is in excellent condition.

 

[Johnnie Walker]

How did the oil look?
I usually run the wix 51515, MC FL1A.

And, a replacement motor wouldn't cost very much if it ends that way.

 

[Agreen]

I wouldn't be surprised if the inside of the engine is horribly sludged. I once worked at a tire store where all I did all day was sling tires and oil. We used whatever the cheapest oil was, and the filters were the lowest quality I've ever seen. Fram makes filters 10x as good as the ones we put on. It was all in the name of selling a $14.99 oil change to get people in the door to tell them they needed more service. A real scumbag place that was. I worked there 3 months.

I also wouldn't be surprised if that oil filter had been on there for a few oil changes.

Keep checking the cut open oil filters. If you start getting glitter in the oil, get a new engine. Fortunately there are plenty of donors available. I'm also surprised you aren't hearing noises at 0-10 psi of oil pressure. That tells me that the sending unit is probably junk.

 

[Anak]

The lack of valvetrain noise is my ray of hope. I can't imagine I wouldn't be hearing a racket if oil pressure were really zero.

I am just wondering how this thing has gotten so much sludge. I thought that was a Quaker State thing from the '70s. I remember tearing down an engine from that era that looked like it was packed with asphalt, but I thought oil technology had improved since then. Could this result from additives, like STP? Just wondering if maybe someone was using something to thicken the oil. Would that lead to this picture?

 

[Runnin'OnEmpty]

I have never seen a filter that clogged!

My immediate concern would be the oil pump pick-up
screen. It could be as clogged as the filter. It might be
worthwhile to pull the pan and have a look. Cleaning the
screen might improve the oil pressure if you're lucky...

 

[Anak]

That is a good point. I hadn't thought about the pickup screen.

I don't think that would explain the low pressure when warm however.

Still probably worth pulling the pan to examine the situation. Which then begs the possibility of putting in a new pump. Which then begs the question of high volume or not. Hmm...

Thoughts on those possibilities are appreciated.

 

[8Mud]

That is a good point. I hadn't thought about the pickup screen.

I don't think that would explain the low pressure when warm however.

Still probably worth pulling the pan to examine the situation. Which then begs the possibility of putting in a new pump. Which then begs the question of high volume or not. Hmm...

Thoughts on those possibilities are appreciated.

Cleaning out the pan and pickup screen isn't a bad idea, at the same time you can check for a main seal leak. One thing that is often overlooked is the oil pump releif valve, they get really gunked up and can stick (closed or open, anybodies guess which). As long as you are in there might as well plastigauge a couple of connecting rod bearings (top and bottom).
Side note I've found a 15 PSI difference in the dash gauge pressure and a mechanical gauge on ocassion, Purge the air out of the mechanical gauge line to get the best reading.
I've cleaned up the pump releif valve, clearance the pump lid, replaced the connecting rod bearings and gained fifteen PSI at idle. Removing the pump cover and throwing away the gasket then using a light coat of silicon can help, the correct cearance is in the book. I've found the real deal Carb cleaner the only thing that actually loosens old oil varnish. Check the clearance with plastigauge before deleting the gasket, you don't want the clearance too tight.
I've used 10-40 in older motors, no reason not to. The only reason for the lighter oils is to improve fleet fuel consumption numers for the EPA or if you live in a really cold climate. Remember these are old school motors, designed a little on the loose side and designed for high mileage.

I lived overseas for decades and there was no corner parts store for Jeeps. Ordering parts could take weeks or months. I learned to make do.

 

[Rob Mayercik]

With all that sludge in the filter, I'm wondering if the oil feed to the pressure sender is restricted too, and preventing a true reading.

 

[Wayne Sihler]

While none of my XJ engines were that dirty, I used Rotella T 15- 40 oil in them.The additives in the desiel type oils helped slowly clean the engine...or so I thought. When valve covers were removed all was clean on top. YMMV

 

[cruiser54]

THIS^^^

You can assess the sludge buildup while shining a light into the oil filler hole.
Napa 1085 with 6 quarts of Rotella
and a quart of Marvel Mystery Oil and watch the sludge melt away.

 

[75SV1]

I too run Rotella. I am running the T6. I use NAPA Gold or Platinum Filters. WIX are good too. I do try and run the oversized filters. I forget the numbers. I would try running some Marvel Mystery Oil for a change. I did replace an oil pump and I run at 50 PSI and probably 20-30 PSI at idle and warm. I would go with a stock oil pump. Check the trust bearing if you pull the pan. Also, I'd recommend changing the harmonic balancer.

Edit: Rotella does make a 10W-30. I have run it in my XJs and my MB 240D.

 

[cruiser54]

With all that sludge in the filter, I'm wondering if the oil feed to the pressure sender is restricted too, and preventing a true reading.

Yes!!

Remove the oil sender and run a piece of wire or a ziptie through the opening into the engine.

 

[Anak]

Things do not appear to be as bad as I feared. Here is the rear main bearing:

And here is the corresponding journal on the crank:

There is the one scratch down the middle, but no major wear. Nothing like the bearings I have seen that show copper over 10% of their area. This is consistent with the lack of metal showing in the oil filter pleats.


It still begs the question of why no oil pressure.


The oil pickup screen does not appear to be plugged. A bit of sludge in a several spots, but by no means enough to substantially affect pressure (sorry for the fuzzy focus) :

The internals are all pretty black however:

This is just how far we managed to get into it this evening. Tomorrow I will pull the pickup and clean it up. I don't expect to get a bunch of sludge out of it, but we will see what happens. I will also pull the cotter pin and see about cleaning up the pressure relief valve. I would prefer not to drop the pump so I don't have to worry about its gasket, but if the situation requires it I will do so.



Plan is to replace the rear main oil seal, clean things up and put it back together. I am thinking MMO and Rotella look like a good prescription. And I want to slap on a real gauge and see what pressure readings look like that way.

 

[Wayne Sihler]

I think that will be good, the Rotella and MMO will clean that up over time, But what do I know

 

[cruiser54]

I think that will be good, the Rotella and MMO will clean that up over time, But what do I know

That woulda been my starting point. Monitor the cleanliness through the oil filler. We're both in the dark, I guess........

 

[Anak]

My fear is that the Rotella and MMO will do too good of a job too quickly and a bunch of sludge will plug up the pump inlet or the filter and then create a real problem.


And I also wanted to make sure the bearings in this thing were still in good enough shape for it to have a future.


Plus, this is a good way for The Varmints to learn to work on a vehicle and to take an interest in the care of the vehicle.

Cleaning out the pan and pickup screen isn't a bad idea, at the same time you can check for a main seal leak. One thing that is often overlooked is the oil pump releif valve, they get really gunked up and can stick (closed or open, anybodies guess which).


Thank you for the suggestion about the relief valve. I didn't think much of that at first, but decided to go ahead and look into it. If anything makes a difference in oil pressure it is likely to be that.


I had thought the relief valve was a ball and spring arrangement, but it is not. It is actually a piston in a bore. These are the components:

Getting that piston to come all the way out of its bore took a lot of cleaning, and once I got it out there was more cleaning to be done. I can easily imagine that thing getting bound up in its bore.


In case anybody else goes down this road, one detail that might be nice to know is that the roll pin is 5/32" diameter:

Note that life is much easier if you don't drive the roll pin all the way out. If you just drive it far enough to let everything past and then leave the roll pin in its bore while you clean things up then reassembly is going to be more graceful. And you don't run the risk of losing the little pin in the first place.

 

[cruiser54]

Absolutely not. Rotella and MMO melts the gunk away. as said before, you can observing it working by peering into the oil filler hole. Done it numerous times.

 

[Runnin'OnEmpty]

You don't need to worry about the oil filter getting clogged.
They have a pressure relief valve that activates if the filter
element gets obstructed.

Changing the oil filter every 500 miles or so would give you
peace of mind that you're getting the sludge out...

 

[cruiser54]

The filter won't clog simply because the combo of Rotella and MMO melts the sludge away.
I changed the filter at 1000 miles and added a quart of Rotella. Went another 1000 miles.
Monitor the sludge through the oil filler. Probably be clean as a whistle in 2000 total miles.

 

[RCP Phx]

My fear is that the Rotella and MMO will do too good of a job too quickly and a bunch of sludge will plug up the pump inlet or the filter and then create a real problem.


And I also wanted to make sure the bearings in this thing were still in good enough shape for it to have a future.


Plus, this is a good way for The Varmints to learn to work on a vehicle and to take an interest in the care of the vehicle.

Cleaning out the pan and pickup screen isn't a bad idea, at the same time you can check for a main seal leak. One thing that is often overlooked is the oil pump releif valve, they get really gunked up and can stick (closed or open, anybodies guess which).


Thank you for the suggestion about the relief valve. I didn't think much of that at first, but decided to go ahead and look into it. If anything makes a difference in oil pressure it is likely to be that.


I had thought the relief valve was a ball and spring arrangement, but it is not. It is actually a piston in a bore. These are the components:

Getting that piston to come all the way out of its bore took a lot of cleaning, and once I got it out there was more cleaning to be done. I can easily imagine that thing getting bound up in its bore.


In case anybody else goes down this road, one detail that might be nice to know is that the roll pin is 5/32" diameter:

Note that life is much easier if you don't drive the roll pin all the way out. If you just drive it far enough to let everything past and then leave the roll pin in its bore while you clean things up then reassembly is going to be more graceful. And you don't run the risk of losing the little pin in the first place.

The Melling pumps just use a cotter key to retain the relief valve in.