danw77

I was given 1999 XJ with 240k miles that the previous owner gave up on due to a low oil pressure issue. It shows about 40 psi on cold start and gradually drops to near zero. I replaced the sending unit and there was no change. I pulled the valve cover and oil pan and the engine is full of sludge. There was about an inch in the bottom of the pan and the pickup was near completely clogged. I thought for sure that was the problem - or maybe the pump was bad - so I replaced both, as well as cleaned out as much sludge as I could. I put the whole thing back together and the oil pressure is still the same. It will idle anywhere between 2-5 psi, and will be between 20-30 when cruising.

Is there anything I'm missing? At this point I'm assuming the engine is on it's last legs.

My plan is to throw in some 50w and hope itakes it until spring when I can swap a new engine into it. I don't have a garage and don't feel like pulling an engine in my driveway in the middle of winter. This is not my DD - it will be a winter beater and my daughter planned to use it to get to work in the snow (she's a nurse - not her DD either). It's not the end of the world if the engine blows, but I'd prefer it not leave her stranded. What do you think the chances are it will last until spring? Maybe another 1k-2k miles?​​​​

tjwalker

It certainly could be the engine itself, but if I were you, I'd seek confirmation of your oil pressure by temporarily installing a "mechanical oil pressure gauge" where your oil pressure sending unit resides.

This won't take long and will give you clear confirmation of your true oil pressure. This gauge can be rented inexpensively from some parts stores; call around for availability. You have not yet ruled out a fault in the dash oil pressure gauge itself. Doesn't happen a lot but it is a variable that you do not want to ignore, otherwise you might be chasing your tail.

Get some hard data with that mechanical gauge to help make your decision. Good luck and keep us updated!

danw77

Sorry, I forgot to mention that. I did verify the pressure with a mechanical guage. The guage on the dash seems to cut out around 5 psi and drop right to zero (like it can't register low pressure), while the mechanical guage will read 2-5 psi, but otherwise it seems fairly accurate.

00t444e

What oil and filter are you using? My oil pressure was about like yours so I switched from 10w30 to 15w40 and it increased it by 10 psi. I always use either a Mopar or Motorcraft filter.

cruiser54

You have little to lose now.

As stated, a good oil filter for sure. Are you driving it regularly? Marvel Mystery Oil will melt the sludge away and you can hope that helps with oil pressure. Factory spec is 13 PSI at idle. You are only 8 PSI away from that.

danw77

I'm running 10w-30 with a quart of MMO and a Mopar filter.

EZEARL

With that must sludge I wonder if the sending unit orifice on the oil filter adapter maybe be partially blocked. You could try removing the unit and crank the engine over to try and clear it. Just remove the coil wire so it won't start and have someone watch.

Any blow by from the valve cover with the oil cap off?

00t444e

So 5 quarts of 10w30 and 1 quart of MMO? That would make the oil thinner, maybe closer to 25 weight or so. Next time try 6 quarts of 15w40 Diesel oil, the higher viscosity will increase your oil pressure, and the extra detergents that are in diesel oil will help clean the sludge out of your engine.

cruiser54

Earl, as always, thanks for the memory trigger!!!

Read this!! https://www.jeepforum.com/forum/f19/...fixed-1304679/

danw77

Hmmm, that makes sense. I was already thinking along those lines, hoping that the somewhat thinner oil with the MMO in it would have a better chance of getting into those narrow passage ways. THe old sending unit I pulled off did look like it was completely plugged.

cruiser54

Do it.

dave1123

I just recently purchased a 2000 Cherokee Sport with the same problem. 125K miles on it. Cold startup showed 40 psi, dropping down to 10 psi at idle after reaching 210*. Engine was totally quiet without even valve clatter. There was no sludge in the valve cover when looking down the oil filler cap, so I took a change and bought it. The oil pressure sender had some oil in the electrical connector, so I assumed it was bad. I bought a new OEM sensor from a dealer for $78 and did an oil change with Rotella T6 5W-40 and a Mopar filter. Now it shows 45 psi on cold startup and 30 at idle hot. I have NOT cleaned out the elbow yet, but that's my next strategy. Thanks for the insight!

When I drained the original oil, it was black and "chunky" as in some globs of thicker stuff splashing on the drain funnel. This XJ has a history of sitting all summer and only being used for winter transportation in the Adirondacks. 125K in 18 years. After 2K miles since I changed the oil, it's getting dark so I think I'll change it again soon. I'll be cleaning out that elbow then. Funny that when the downstream converter and muffler fell off, it was parked since June after passing inspection in February. It still passed inspection without the downstream converter because it's CA emissions. When I cleaned out the interior, I found a Haynes manual with notes in the margin on the pages about R&Ring the oil pan. I'll bet the PO replaced the oil pump!

cruiser54

You can monitor the progress by shining a light into the oil filler hole.

Has it used any oil? If you can put a quart of MMO in there before the next change at like 3000 miles, it would be good.

dave1123

Mind like a steel trap! I've noticed a rainbow of oil sheen on slush under the jeep after coming out of a store. In 2K miles the oil level has only dropped 1/4 quart and the filter adapter is leaking. Something else to fix! I'm 74 yo and have no garage. Working in the cold numbs my fingers very quickly. I haven't completely finished cleaning up my electrical problems and putting the panels back on yet. My WJ's cracked piston skirt is starting to get noticeably noisy under load so I may be addressing that real soon.

Happy New Year! Then comes the IRS! I have the self employment penalty to pay because my employer won't give me a 1099misc. It's always something cleaning out my wallet!

Shining a light down the oil filler hole was the FIRST thing I did before I bought it! 0331 head on this thing!

cruiser54

Sonsa*****es!!!