I just changed the oil pump and cleaned out about a 1 inch layer of sludge out of the bottom of the oil pan on my 96 GC and now it is doing the same thing again, just not as bad. I can crank it up after it has been sitting a little while and the oil pressure is great, about 50 psi, but after driving it will fall to 20 psi. Also if I run it wide open it will sometimes fall to 0 psi. Any suggestions on what to do? I really don't want to drop the oil pan again but I prob don't have any other choice.

 

It wasn't the pump. Did you check the oil pressure with a mechanical guage?

 

oil sending unit maybe?

 

I am going to check the pressure with a mechanical gauge when I get the chance but I am thinking there may have been some sludge up top that has made it to the bottom. If it is more sludge is there any good ways to go about flushing it out?

 

If you had a lot of sludge in the pan, you most likely have a bunch of sludge in the top end too. That sludge is keeping the oil from flowing back down to the sump fast enough to start the whole oiling process over again when you're really romping on the skinny pedal. You could try some sort of motor flush, Seafoam, or a quart of ATF in the crankcase for a couple hundred miles, then drain the oil and change the filter.You may have to do it a few times.

 

What would cause sludge build up? My uncle used to tell me to NEVER use products like STP because he showed me build up on valve covers caused by it.

 

Lack of regular oil changes.

 

Correct me if I am wrong but if the oil wasn't draining back from the top end fast enough then I could shut the engine off for a couple minutes to allow the oil to drain back down to the bottom end and then when I crank it back up it should have good oil pressure. That's not the case. It has to sit for probably at least 30 minutes before I can crank it up and have good oil pressure. I think that's how long it takes the sludge to settle to the bottom of the pan. Whats your thoughts on flushing with diesel or something like that.

 

I prefer a slow clean as opposed to a quick flush. Try 5 quarts of Rotella or a good synthetic oil and the last quart of Marvel Mystery Oil (or however many quarts your v8 uses...). I use it personally and it does a great job of cleaning things slowly, and once it's in good shape I just keep up with regular oil changes using full synthetic.

 

Well I pulled the oil pan for the second time and found a lot of carbon in the pickup tube and a little in the oil pan. Got everything cleaned out and put back together and guess what..... I drove about a mile down the road and the oil pressure dropped off again. HOW DO I GET ALL THE CARBON, SLUDGE OUT OF THE MOTOR???? And yes I did check the oil pressure with a mechanical gauge.

 

as someone else said, change the oil and for the last quart use ATF, its a much higher detergent than regular engine oil. run it around for a little bit, change it and repeat.

 

What weight oil are you using, and have you added any oil additives/stabilizer ?

I doubt its a carbon/sludge problem. If the build up is that bad, I bet damage has already been done to the internals, mainly bearings. If sludge or buildup was the issue then the oil pressure problem would be more constant and not follow a hot/warm type cycle, the sludge does not do much traveling around in the engine.

When your engine warms up, metal expands and bearing tolerances increase, this increase allows more room for oil flow and/or leak out of the bearing gaps. This is probably where your oil pressure is going. Sadly the remedy can be expensive, but you could try a heavier oil like a 30w or even one of them thick oil additives like Lucas or STP to buy you some time.

 

Right now I am running delo 15w40 with a quart of marvel mystery oil. Today i drove the jeep around taking it easy, not getting the rpm's above 2500, and the oil pressure was 25 psi at idle and 50 psi above idle so I believe the bearings are fine. Soon as i go WOT the pressure falls off and doesn't come back to normal. So I am thinking at WOT its sucking up the carbon in the pick up screen. I need something to break down the little pieces of carbon.

 

What I would worry about is how much of that other sludge and carbon are you going to break loose in the engine to try to clean the little amount that can stop up the pick up screen. Have you looked down in the valve cover yet, should be able to remove the oil cap and see a little bit down there. If you had heavy sludge in the pan, its probably uglier on the top of the engine.

If that gunk is stopping up the pick up screen, its more than likely going to be stuck on there. I just cant see it getting sucked up there at higher RPM and then fall back down at lower RPM.

 

Once it stops up at higher rpm's I have to shut the engine off for a couple minutes to let it settle back down and the oil pressure still doesn't quite go back to normal after that.