Low oil pressure caused by sludge in oil?

CODE5

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Brief backstory: I had a blown head gasket and cracked head on my 02' 4.0L. The engine was VERY sludgy when I opened the valve cover, not black sludge — more like chocolate milkshake sludge. I got most of it out that I could but I know there are remnants in the engine. When it came time to add oil I did 6 quarts of 5w-30 conventional and a bottle of MMO (hoping to clean out the crud) I went with a new WIX oil filter as well.

On my first drive I noticed good oil pressure (40 psi) until the engine temp reached 210F. The psi was fine while driving but when I stopped at a red light it quickly went down to 10 and then 0 down to the "CHECK GAUGES". As soon as I started driving again the psi went up to about 20.

As for "did you check the sending unit?" Yes, I installed a new Mopar one back before I did the head job.

So I've been reading various threads about low oil pressure but I haven't exactly found the answer to my question. So my question, is this low oil from all the nasty crud I'm trying to flush out and it will get better once I do a flush? OR are the bearings / camshaft / engine internals on their way out the door? And I'm better off saving up for a used engine?

Thanks - I am new to working on Jeeps and engines in general... I downloaded the FSM and watched lots of YouTube videos to get the head cylinder installed in my driveway so I'm trying to learn along the way :)
 

97JadeTJ

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The older TJ‘s had a real oil pressure gauge which fluctuated with rpm’s… general rule of thumb is 10 psi per 1000 rpm… that choc milkshake was probably water mixed with the oil from the blown head gasket…that being said a quick replacement of that oil filter will tell you If it’s clogging up… My 2.5L hovers around 40psi while moving and drops way down when stopped…if it were me and I had a lot of that sludge in the motor I’d do another oil and filter change after a couple hundred miles…
 
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JKP

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Your pump screen may be clogged by the sludge. I'd drop the oil pan and clean it out.

Depending on how long it ran with antifreeze in the oil, your bearings may have been wiped out.

You might try a high mileage oil as well to help clean it out.
 
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CODE5

CODE5

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The older TJ‘s had a real oil pressure gauge which fluctuated with rpm’s… general rule of thumb is 10 psi per 1000 rpm… that being said a quick replacement of that oil filter will tell you If it’s clogging up… My 2.5L hovers around 40psi while moving and drops way down when stopped…if it were me and you had a lot of sludge in the motor I’d do another oil change after a couple hundred miles…

That is my plan - I'm thinking if I can get a couple hundred miles on this oil I'll replace it with 10w-30 and a new filter.

Your pump screen may be clogged by the sludge. I'd drop the oil pan and clean it out.

Depending on how long it ran with antifreeze in the oil, your bearings may have been wiped out.

You might try a high mileage oil as well to help clean it out.

It ran for about 100-200 miles before I found the milkshake oil so it wasn't too long I don't think. If I had not found the nasty oil and noticed the coolant loss I'd have assumed the engine was fine it ran so well honestly...
 

macleanflood

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I had really sludgey oil in my 97. When I changed the oil the oil pressure sender failed. You might just need a new Mopar sender.

You might want to pull the pressure sender and run a pipe cleaner down the orifice. I've heard of folks loading up a sprayer with ATF and hosing out oil passages too...but have not and did not need to do that on mine.

Verifying the pressure with a manual gauge would be good.

And then there's the ignore it... assume you have some pressure since it's not making valve noises/upper end noises and run it a bit...get it good and hot...and do a couple of oil changes and see what happens over the next couple hundred miles.

-Mac
 
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CODE5

CODE5

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I had really sludgey oil in my 97. When I changed the oil the oil pressure sender failed. You might just need a new Mopar sender.

You might want to pull the pressure sender and run a pipe cleaner down the orifice. I've heard of folks loading up a sprayer with ATF and hosing out oil passages too...but have not and did not need to do that on mine.

Verifying the pressure with a manual gauge would be good.

And then there's the ignore it... assume you have some pressure since it's not making valve noises/upper end noises and run it a bit...get it good and hot...and do a couple of oil changes and see what happens over the next couple hundred miles.

-Mac

This is the noise it is making 😬 however I think it is an exhaust leak from my poor job of bolting the manifolds back on when I did the head job.

 

hear

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I guess I'm a little surprised you had sludge on the top end but didn't remove the pan to see what you had on the bottom end. At the very least I would have wanted to see what was on the pump screen.
 
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CODE5

CODE5

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I guess I'm a little surprised you had sludge on the top end but didn't remove the pan to see what you had on the bottom end. At the very least I would have wanted to see what was on the pump screen.

Contents inside the valve cover… head clearly had a crack between cylinders 3/4. Will be unbolting the exhaust so I can drop the pan to see what is inside when I drain the oil here soon.

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Akitadog

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They make a flush to use before an oil change.

My father being a mechanic new little tricks he learned at the Postal Garage.
He would add about a half a quart of automatic transmission fluid just before an oil change, I would be amazed how it would clean up under the valve cover.

I would not use AT fluid today, since there are flush products available for this now.
 
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RMETeeJay

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Agree to using a motor flush before draining. I wouldn’t normally recommend it, but in your case it should help suspend additional crap so it will drain out. Post some photos of the pan and screen if you think of it.
 
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CODE5

CODE5

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So… I get home from work and go to crank up. Immediately I have 0 oil pressure “Check Gauges” I cut the Jeep off and walk over to the oil sending unit. I figure why not unplug the electrical and when I do it makes a gushing sound and oil comes out. Guessing that unit is TOAST?
 
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CODE5

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Least you got it before it pumped the ECU full of oil. Happened to someone on here.

-Mac

Yeah, I saw that. Still hard to believe but I don't want it to happen to me - yikes. I'm going to at least try and clean that port first while I'm waiting on another unit.
 
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CODE5

CODE5

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Also a great time to get a oil pressure test gauge and get the actual oil pressure.

Another trip to the local parts house! Not a bad idea though. I’m going to check and see if a few local friends of mine have one first.
 
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