Low Oil Pressure (Not The Sensor)

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RedWranglerRedWrangler

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Found lots of threads about low oil pressure on the dash gauge. They all seemed to resolve with replacement of a new mopar oil pressure sender or the thread was abandoned. I may not be so lucky.

In my case:
  1. Red Check Gauges light at cold startup & 0 oil pressure on dash gauge. No weird engine sounds, driving characteristics, or engine codes
  2. I replaced the sensor with a new mopar sensor from Rock Auto.
  3. On cold start, dash gauge reported 30psi at idle. But, oil pressure fell as the car warmed up. Once at temp, oil pressure showed 0psi & check gauges at idle and 10-20psi when on the gas.
  4. Shop confirmed that a mechanical oil pressure gauge agreed with the dash gauge. They also said the valves, oil pan, and oil pickup screen were full of sludge. Thanks PO.
  5. Shop threw in a new oil pump, flushed the oil, and replaced with some sort of Liqui Moly 20w50 oil and an additive to help with the sludge.
  6. Now, dash gauge shows 40-50psi on cold start idle but once up to temp, it still falls back down to 0psi + check gauges and 10-20psi while on the gas. Still no unusual engine sounds, driving characteristics, or engine codes.
Shop said bearings are probably worn from lack of oil changes by PO. I might get a couple years out of it but then it'll be time for a new motor.

What say the brain trust?

Should I not sweat it since the car behaves fine otherwise? Am I good to stick with that 20w50 in there or is that an ill-conceived band-aid?

--One-thousand thanks from a Jeep newb.
 
In my exp rod and main bearings that are shot crate a pretty good rattle on cold starts for several seconds till oil is pumping good. Kinda of a stretch you get 50 at start now but still it drops to 0 at idle once warmed up. general rule of thumb is 10 psi per 1000 rpm. If it were mine Id be a tad Leary to venture in to the deserts or on a long trip with what you have for pressure.
 
Get some Plasti gauge...pull the oil pan...you can usually change the crank bearings by just rolling in the top one.

But yeah better off with a complete rebuild or replacement.

-Mac
 
Is there any chance my engine is ok and this is caused by something more minor? That there's no unusual noises or behavior is what's giving me mixed messages.

I wasn't originally planning to use this for road trips, but I don't want to worry about some catastrophic failure every time I take it out for a spin.
 
Always a chance but it's slim. Cold be that new oil pump is bad... wouldn't be the first new part that was bad out of the box...or died from all the crap in the engine.

No oil pressure is just that.

A compression test would be good at this point...borescope down the spark plug holes will tell you if the cylinder walls are scored.

I'd pull the oil pan and get a main bearing out...if you see copper you're in trouble.

Right now you have a chance to fix it...and I think you're going down the right track...but...no oil pressure is just that and oil sludge...all sounds bad.

-Mac
 
More info would be nice …. 4 liter? What kind of miles on it?

If a mechanical gauge is verifying your sending unit / electrical gauges then things not looking good. Seeing a couple bearings could confirm your suspicions.
 
Since you have replaced the oil pump (what manufacturer?) and have flushed the oil system to remove the sludge; as others have recommended.... remove the oil pan, pull several of the crankshaft main caps, do a visual of the crankshaft journal bearings and crankshaft; then have the journal measured and test with plastic gauge to get the clearances.
More than likely the journal bearings are worn.
 
You wont hear any engine noises until parts start to wear quite bad due to lack of oil. If your big end bearings start to wear they will knock quite loud as they get worse but usually you will experience lower oil pressure as you accelerate not at idle and then less PSI on acceleration/Revs? Yes the 20w 50 is a Bandaid fix unless you are running it for really high temperatures on a worn engine. Seems your oil pressure drops as the oil gets thinner. Once your big end bearings start to knock if they do you need to stop and rebuild.

Its pot luck at the moment because you have just been to a mechanic and they said you "could" be good for a few years but if they believe the bearings are worn due to sludge and lack of oil changes then it will only get worse. They tested the oil pressure so you know for sure you have zero pressure at hot idle therefore its not a sender, switch or computer problem.

Trying to get advise from a Forum is generally fruitless in this situation because you already have first hand mechanical advise from mechanics who have already worked on it and seen/ heard it running.

Peace of mind would be to start repairs now and don't delay because you will forever wonder if and when it will be too late. I had an oil pump fail on a freeway and it doesn't take long before those bearings start knocking loud. you need to weigh up the costs of fixing it now against possibly having it towed at the most inconvenient moment or being stranded without a vehicle when you least expect it!

My oil pump failure (not TJ) happened on the way to a long weekend camp with many friends and It was ruined!
 
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Reactions: flyinfish and CharlesHS
A motor swap might be the quickest and cheapest option. No oil pressure is like your heart stopping, it doesn't end well! Use the little time you have left to formulate a plan to rebuild or replace short block, long block or complete engine.
 
I'd buy or rent a mechanical oil pressure gauge. Change the 20w-50 a few times withing a month. Maybe 200 miles between, you don't need additives, cheap store brand oil will do a good job cleaning out the crud. With 20w-50 oil running in the engine if you get a few psi at idle and the engine is fairly quiet just run it. It'll get noisy when the bearings continue to wear, you are still going to have a good core when it does. It might last another 10 years running like that, just go easy on it. There is no reason to pull the pan and check a thing unless you personally are going to replace the bearings. Most people don't rebuild their own engines so that's really why I'm suggesting this route.
 
I would check yourself with a mechanical gauge. Mine has done it, every time I drive over 20 mins, for 2 years, but I really have between 10-14 psi at idle. The factory sensors say 8-14 psi on them, so I'm guessing its due to that. I keep a separate mechanical gauge at all times. See if the shop wasn't just making money... I've replaced the sensor repeatedly and with a Mopar the last time.
 
Thanks all. With a new engine on the line I'm going to rent a mechanical oil pressure tester to confirm for myself.

If I do in fact need and decide to go the rebuild / replacement route, what are my best options? My priorities would be cost, reliability, resale value, fun factor in that order, and it needs to meet California SMOG certification.

I certainly didn't expect this much heartburn from this thing. Maybe I should just sell it as-is and try again.
 
Basically you rebuild yours...find a used replacement...find a new replacement...4.2 stroker motor...5.2 v-8...Cummins crate diesel...VW diesel...LS swap...

Lots of options. Lots of forum posts covering them.

Hard decisions to make...good luck!

-Mac
 
How many miles on your engine? If it was poorly maintained for a very long time, a rebuilt engine with a warranty is not a big job or that costly. Half of the fun of a TJ is lovingly refurbishing them.
 
RedWranglerRedWrangler said:
Found posts on other forums about those with the same symptoms which were resolved by cleaning the oil pressure sensor port with a pipe-cleaner and trying to blast out any blockages so going to try that as well. https://www.jeepforum.com/threads/4-0-low-oil-pressure-at-idle-fixed.1304679/

Never say die!
Click to expand...
Running ATF instead of engine oil...or a mixture thereof for a couple of minutes can clean things up. ATF is thin and has a lot of detergents.

-Mac
 
RedWranglerRedWrangler said:
160K and the more I learn about it the more it appears to have been poorly maintained.
Click to expand...
These engines are reasonably forgiving and some here have some incredible amounts of miles on them. 160K is nothing. I wouldn't run ATF in it, but there are additives like Mystery oil which can help clean things up. Notice I said additive. If it is not knocking or protesting, it may not be as bad as you fear. I assume your TJ is an older model as the gauge on the later ones is more for show.
 
Flivver250 said:
These engines are reasonably forgiving and some here have some incredible amounts of miles on them. 160K is nothing.
Click to expand...

That's what I keep hearing 🤞

Flivver250 said:
I assume your TJ is an older model as the gauge on the later ones is more for show.
Click to expand...
Yea 2000 with the "real" oil pressure gauge.

Another data point I just realized may be connected — when I took it to Shop #1 to hunt a coolant leak, they detected a very low level (60 or 90.. ppm I think) of hydrocarbons in the cooling system (radiator I think) using a digital gas analyzer, indicative of cracked head / gasket. Although there were no other symptoms of that (clean oil, clean coolant, no exhaust smoke, no codes, etc.. etc..). Radiator was cracked so we chalked up the coolant leak to just that and the low-level hydrocarbons to test contamination.

Fast forward and now I'm wondering if there is in fact a small crack in the head / gasket leaking coolant into the engine and wearing things down causing low oil pressure. Pretty sure I do have the infamous 0331 head, and the PO did an oil change a couple weeks before I bought it so maybe that's why the oil appeared clean.

On the flip side of the coin, Shop #2 who found the sludge and replaced the oil pump also performed a chemical block test which came back negative for hydrocarbons...

I got a mechanical oil pressure tester and pipe brushes en route to clean the oil pressure sensor port and test the pressure for myself. Holding out a sliver of hope that clears things up.
 
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