oil pressure??

[FlxnXJ]

last trip out in noticed my oil pressure had dropped, and on hills it would acually start ticking, untill I gave it gas, once warmed up and sitting at idle, I have about 12 lbs of pressure!

Anyone else have this happen?

Iam guessing I need a new oil pump?

 

[RichP]

What brand oil filter ?

 

[sgtmack]

Have you checked the oil level? Unless it's low, hills shouldn't make a difference.

In 20 years of wrenching, I can count the number of bad oil pumps I've seen on one hand. But I have made a pretty good living rebuilding engines. Normal symtems are lower oil pressure the warmer the engine is, and lifter noise at idle.

Have some one check it with a mechanical gauge, and if it's low warm, pull a bearing cap.

P. S. Sorry for the spelling, now you know why i work on cars, and not in an office.

 

[sgtmack]

I should have also asked how long it's been since you had an oil change?

 

[FUNKYTEE5]

last trip out in noticed my oil pressure had dropped, and on hills it would acually start ticking, untill I gave it gas, once warmed up and sitting at idle, I have about 12 lbs of pressure!

Anyone else have this happen?

Iam guessing I need a new oil pump?

I don't know the year of your XJ is, but my 93 4.0 had the same kind of issue. The factory oil pump in mine was aluminum which have been known to wear out at over 140k or so. My oil pressure started going up and down by 10-15 pounds at idle and sustained steady rpms. Idle pressure was erratic and down to 15psi with the valvetrain ticking loudly. I knew the bottom end was tight so I suspected the oil pump. I got a Sealed Power pump and it was cast iron. Now idle pressure is back to 40-50 warm and almost 80 cold. After inspecting the old pump I found that the drive gear was sloppy and eating into the housing. I would also suspect that the bypass spring was fatigued. But it's all good now with a new oil pump. Before you do anything, hook a analog gauge up to it where the pressure sender is and double check your pressure!

FUNKYTEE5

 

[Eagle]

last trip out in noticed my oil pressure had dropped, and on hills it would acually start ticking, untill I gave it gas, once warmed up and sitting at idle, I have about 12 lbs of pressure!

Anyone else have this happen?

Iam guessing I need a new oil pump?

12 psi is basically okay (almost) Factory spec is 13 psi at warm idle. Pressure when running under load is more critical. The factory service manuals say 13 psi minimum at idle, 37 to 75 psi above 1600 RPM. Most new XJs seemed to run about 50 to 55 psi at highway speed. For an older one, if you have 35 to 40 psi or better at highway speed you should be in good shape.

 

[FlxnXJ]

Well, I changed the oil about 60 miles ago. Iam running an STP filter. Iam on my 3rd 4.0L. They dont like to run upside down and This motor has about 40,000 miles on it I guess. I installed it when It was still a daily driver.
I guess Ill buy a pump, and check the rod bearings when I pull the pan. The engine has gotten hot a couple of times but not for a long period of time. No valvetrain or lower end noise, except on very steep hills, and it goes away as soon as I rev it up, to give it oil pressure.

 

[ZmOz]

I would start by changing the oil pressure sender. It is EXTREMELY common for them to cause false readings on a 4.0.

 

[FlxnXJ]

I have an aftermarket gauge, my XJ only has light gauges stock.

 

[FUNKYTEE5]

I have an aftermarket gauge, my XJ only has light gauges stock.

Try a new pump preferably cast iron Let us know what the deal was. I'm curious to see if it was the same issue as mine.

FUNKYTEE5

 

[Dr. Dyno]

I would start by changing the oil pressure sender. It is EXTREMELY common for them to cause false readings on a 4.0.

While it IS common for the sending unit to give false readings, I'd verify them with a mechanical gauge before rushing to spend lots of moolah to replace a sending unit that might turn out to be good. I think that applies especially in FlxnXJ's case because his engine starts ticking when his gauge reads low, and that indicates to me that the oil pressure really is low when that happens because the lifters are not staying pumped up (they need at least 13psi).
Since the ticking only happens on steep hills, that suggests that the oil pump pick up is being starved of oil (especially if the vehicle is facing steeply downhill because the sump and oil pump pick up are at the back of the engine). This can happen for three reasons; too little oil in the pan (did you check the dipstick?), blocked oil pump pick up screen, or defective oil pump.

 

[ZmOz]

I'd verify them with a mechanical gauge before rushing to spend lots of moolah to replace a sending unit that might turn out to be good.

New sending units are only about $15...cheaper than a mechanical gauge. (although it sounds like he already has a mechanical gauge)

 

[FlxnXJ]

Ya, the oil level is fine. Its only ticking on up hills, after hammering on it really hard, and letting off the gas, and I really dont think it was in a position to cavitate, so Iam going to put a new pump in it, and Ill let you guys know what happens, but I have to finish triangulating my front end and getting my hydro steering finished 1st. to many project at once :repair:

 

[Dr. Dyno]

New sending units are only about $15...cheaper than a mechanical gauge. (although it sounds like he already has a mechanical gauge)

I wish sending units were that cheap over here. I paid $50 to replace mine last time and that was at least five years ago.

 

[Pete M]

The last time I had low oil pressure problems it was due to collapsed oil filter innards (Fram). A new filter cured it.
Jeep on!
--Pete

ComancheClub.com

 

[FlxnXJ]

Well, I threw a set of rod bearings in the old 4.0L, and a new high Volume oil pump. Pressure is 40 psi at idle when warm, sure beats 12 psi :repair:

It went from 40 psi at startup to 60 psi, From 20psi to 50 psi at cold idle, and from 12 psi to 40 psi at warm idle!

 

[FUNKYTEE5]

Well, I threw a set of rod bearings in the old 4.0L, and a new high Volume oil pump. Pressure is 40 psi at idle when warm, sure beats 12 psi :repair:

It went from 40 psi at startup to 60 psi, From 20psi to 50 psi at cold idle, and from 12 psi to 40 psi at warm idle!

Were the old rod bearings sloppy? How'd the old oil pump look? Good to hear it's got good blood pressure

FUNKYTEE5

 

[FlxnXJ]

Bearings had wear, they were due to change. the pump wasnt really sloppy, but I figured change it whille its apart.