Low Oil pressure at idle

First - yes, I've searched the posts and didn't see any that directly addressed this.

My '98, with 153K miles has about 10 PSI oil pressure at idle when fully warmed up.

When it is cold, it has about 50 PSI at idle, and it gets progressivley lower as is warms up - eventually down to 10 PSI after 20 miles or so. It kind of fluctuates between 10 and 13 PSI, actually. The idle speed is constant.

I've changed the oil, filter (not a Fram), and sending unit.

It consumes less than 1/2 quart between changes at 4000 miles, so I don't think the motor is very worn. Thanks.

What oil are you running?

Mobile 10-30. 10-30 what is recommended in the owner's manual, although I've considered going heavier.

I also have a '99 with 111K miles, I run the same oil and it never gets below 40 PSI.

I had the same problem. Try a K&N, Wix or Mobil 1 filter. It's amazing what a good quality filter will do. If that doesn't bring up the oil pressure at idle, replace your oil with a heavier weight (I use Mobil 1 15-w-50 weight oil in the summer). Early on I tried Lucas oil additive and 20-w-40 dino oil. It sure did bring up the oil pressure, but some of the folks on this board are adamant that Lucas oil additive is not good for an engine. Use the search function on Lucas oil additive and you should find those threads.

If none of the above works you will want to consider replacing the bearings on the crankshaft. Not an impossible job on an XJ for us amateur mechanics. And yeah, the oil pump, too, while you're in there. Again, use the search function to get more on this.

What you do NOT want to do is run the engine at low idle oil pressure.

Replace a quart of oil with Lucas synthetic oil additive until your next oil change. If the oil filter is not fairly new you should replace it just in case there is a problem with the filter itself. If the problem started right after an oil filter change, then replace the oil filter right away with a known high quality filter like K & N or Mobil 1.

If the oil pressure still drops below 13 psi after adding Lucas (and maybe the filter) then change the oil to a good quality 10W40 or 20W50 synthetic, with a new filter. If both of these fail then pull the oil pan, check the oil pump pick up tube and inlet screen for any problems, sludge or blockage. While in there you should check & inspect the main crank bearings and rod bearings for wear or damage. Unless you find an obvious problem you should replace the oil
pump with a high flow rate pump. Then seal her up, pray the force is with you and start it up.

x2 on using the lucas oil, I gained nearly 5lbs of pressure at hot idle.

I was also having low readings just like you, and the lucas oil definitely helped, so try it!

I'll give the Lucas a try and report the results.

pick up some main bearings, rod bearings, and a gasket while you're there-- if the pressure is good cold, your pump is working, but as it warms up, the clearances are growing beyond spec. Thicker oil (or Lucas) will band-aid the problem, but won't fix the bearings.
just my .02 worth

--Shortyeace:

Before you blow a lot of money, beg, borrow, or steal a mechanical oil pressure gauge. Dash gauges are notorious for being bad.

As for low pressure at an idle, thicker oil will help. Tons of vehicles run with that kind of pressure for years before any problems, if ever. Your ear is your best gauge. If it is making a knocking / rattling noise, its time to refresh the engine.