low oil pressure

i have plenty of oil, but my oil pressure is running about 20, it runs 40-50 withen the first 5 minutes of driving if it hasnt been driven for a few hours, but after that about 20, could it be an oil pump or what?

i had the same problem on my 90 xj but was lucky enough that it was only my oil sending unit....may want to check that out...

What year XJ, what engine, how many miles, and what type and weight of oil are you running?

1992, 4.0, 183k miles, 10w30

how do u check oil sending unit?

well, mine has been running kinda weird lately. It does something similar, up around 40-50 when i start but then when i stop and idle at a light it will drop down to 20 but when i start driving it will go back up to 40-50.

Don't know if this is normal or not but haven't though anything of it. 1999 4.0 66k miles 10w30

Hodge

Mine runs at 60 lbs @ highway speed..... around 35 idle. It used to run at 40 Highway and 15 to 20 idle. At the last oil change I ran some kerosene throught it (at idle speed for about 5 min) and my pressures have been great since!!!
--http://forums.vmag.com/cherokee199/messages/11840.html

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Interesting.. running kerosene through my engine kinda scares me though :firedevil mUhahahaha!

xjndmud said:

i have plenty of oil, but my oil pressure is running about 20, it runs 40-50 withen the first 5 minutes of driving if it hasnt been driven for a few hours, but after that about 20, could it be an oil pump or what?

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If it's running (not idling) at 20, there is a problem. Factory spec for a warm engine is a minimum of 13 psi at idle, and 37 to 75 psi above 1600 RPM. 10W30 is one of the specified oils for your year.

As already suggested, the oil pressure senders are notoriously inaccurate. I'm on the third or fourth in my '88, and it is now bad (40 psi idle, 42 psi highway -- don't think so). They're cheap, so step one is to change that. The sender is located just above the oil filter -- looks like a cigar with a wire stuck onto the end.

If that doesn't work, try using heavier oil. Some of the major companies offer 20W50 in conventional oils, and Mobil-1 has a 15W50 in synthetic if that's what you run.

If that still doesn't bring you within spec, it's either an oil pump or bearings. In the 4.0L engine, rod bearings seem to wear before main bearings. The bearings can be changed with the engine in the vehicle by dropping the oil pan, and it sounds like you should be preparing to do this. You could change the oil pump while the pan is down, but many folks find that's unnecessary. If the rod bearings are worn down to where the copper shows through, that's your problem.

When reassembling, get the one-piece pan gasket for a '94 or newer engine. You also might as well do the rear main seal while the pan is off.

thanks guys, i'll let you all know how it works out

I have a 92 as well with the same problem, only mine is also knocking in one of the first two cylinders. Is yours making noise as well?

I'm planning on replacing the rear main seal and the rod bearings as well. Hoping the bearings will stop the knock and the seal (right now better referred to as a seive) brings my pressure back up.

well my first 4.0 did the same and sounded like a rod was knocking, and one day one the interstate the oil pressure dropped to 0 and the temp when all the way up, and before i could do anything it cut off, i burnt the valves, but this new rebuilt one isnt knocking. i just changed my oil pressure sender, so now im goin to change the oil, and see what happens

You didn't mention that the engine doesn't have 183k miles on it. A fresh rebuilt should not have low oil pressure. Check it with a mechanical gauge and if it's out of spec I'd suspect that whoever rebuilt it didn't use the right bearings. In that case, I would check both the rods and mains with plasti-gage, and expect to have to replace them all.

u are correct, i failed to mention that

note to self. before adding oil because you think its low, pull the dipstick and check it. i changed my oil and let out dern near 15 quarts of oil that i thought i was burning. stupid me. i changed my oil sending unit and all seems to be well now. at idle it runs about 20psi and running it runs from 40-60. thanks guys

?

Cut an oil filter to see if there are any metal particles.

With that much oil in it, the rods were probably dipping into the oil and whipping it into a froth. You weren't pumping oil, you were pumping froth.

lol, probally so, it seems to be doing great now though, thanks for all the help guys, i got stuck yesterday, but "Where there's a winch, there's a way!"