I've been having some sporadic problems with my oil pressure for quite a while. I replaced the sending unit last year and nothing changed at all. Here's what happens: About 20-30% of the timesI start my jeep, the oil pressure goes straight to max and stays there. When this happens, there is a LOT more clicking coming from the valve train, so I'm pretty confident it's not properly circulating oil. Now that I'm in the habit of watching my oil pressure gauge, I usually notice right away and shut it off, wait, and restart. Often, it goes back to normal after the first restart, and never takes more than three tries for it to start up and run normally.

Again, there is no doubt in my mind that it sounds different when the gauge is high (3rd-generation mechanic from mexico once stopped in his tracks while walking by me and told me my car was making the "chicken sound!") So I'm sure it's not a sensor issue (unless the feedback from the sensor somehow affects oil flow, but my understanding is that all it does is send current to the gauge).

Also, on very rare occasions, the oil pressure runs low at idle (around 20 psi, halfway to the middle of the gauge). "Normal" oil pressure for my jeep is ~40 at cold idle, 35 at hot idle, and ~50 when cruising, so something out of the ordinary is definitely happening that makes it drop.

Any thoughts? Sorry to type so much for such a simple question but I wanted to make it clear that my problem is a bit unusual. My uneducated opinion tells me something is physically blocking the flow of oil so it's getting backed up and reading high pressure before the blockage, but not getting enough flow after the blockage. But I have no idea what this "blockage" could be.

Thanks.

 

Remove the oil cap on the valve cover. Look in with a flashlight and see how sludged up it is.

 

Will do. If there's a lot of sludge there, does that tell me my engine as a whole is badly sludged, or just that it's not flowing properly up by the valves?

 

Shouldn't be as bad down below the head but would still need attention. What year xj and what motor?

 

2000, 4.0

 

If it is sludged, resist the temptation for a quick fix. First, fix the engine's breathing problem. Your CCV valve (valves? not sure on a 2000) isn't working. Fix it. (Replace it.)

Now, clean up the sludge. There are engine flushes you can get that will dissolve the sludge, but the problem is, you run the risk of it working too quickly, and breaking off chunks which can clog oil passages. Bad things happen.

Instead, start changing your oil every 500 or 1,000 miles. Instead of adding 5 quarts of oil, add 4 quarts and a quart of Rislone. Make sure you change your filter with every oil change.

That will clean things up slowly enough that there is no risk of breaking off chunks. Give it 5,000 miles or so and you'll be cleaned up.

BTDT.

 

Thanks for the tips. After other research I'm pretty sure it's sludged, so I'll take my time and try to work through it

 

I have a 95 XJ 4 liter,new engine about 7,300 miles on it, I heard noise so I pulled the valve cover did not see a lot of oil coming up the pushrods. I have some clattering going on below. So I pulled the head , cam and lfters. I found both the lifters and cam badly worn. So I change the cam and lifters. I still have noise, still have no flow I have plenty of pressure but no flow to the top.
I also had the valve springs checked, they are the right ones and are good.
I wonder if there's blockage in the oil galleys.
????