new XJ - oil pressure problem

So, I picked up a '98 classic, up country suspension, and 84,400 miles. It is in great condition, an old couple owned it before, and garage kept, blah, blah, blah. Anyway, I thought it was a good deal until I brought it home. I think I could shoot myself for missing a couple of things while rushing through checking it out.

1) Noticed it had a tc drop, but after some searching, it seems to be normal for an XJ with the UC package. No big deal.

2) Didn't really inspect the rear main. Looks like it may have a very slow leak.

3) When I got back from the test drive, I noticed the oil gauge went down to 10 psi. Revved the motor, and the pressure goes up to 45. So, I thought I'd just replace the sending unit. Replaced the unit the next morning, and no change,so I decide to do an oil change. I put in mobil 1 oil and a napa gold filter. Nope...nothing. 40 psi while driving, and 10 psi at idle.

My next step is to get a mechanical gauge to check. If it reads good, no problem, but what if it doesn't? Should I drop the oil pan to check the pickup? Drop the pan, replace pickup, oil pump, and rear main while I'm there? I'm kind of at a loss. Other than these couple of issues, it is a great new addition.

Any other viable tests for the oil pump? Would it be a good idea to run some Seafoam through, or some other cleaner?

What do you think? TIA

How does the pressure behave when cold? If it's good when cold, bad when hot, then it's probably either the pressure regulating spring gone soft, or the pickup tube is loose where it goes into the pump body. It needs to be really tight to keep from sucking air in when the oil thins out. Had that with my pickup.
Wayne

when it is hot, does it knock when you start it after it has sat for awile?

XJ Jammer said:

How does the pressure behave when cold? If it's good when cold, bad when hot, then it's probably either the pressure regulating spring gone soft, or the pickup tube is loose where it goes into the pump body. It needs to be really tight to keep from sucking air in when the oil thins out. Had that with my pickup.
Wayne

Click to expand...

When cold, at startup it is around 50, and idle 25.

scottmcneal said:

when it is hot, does it knock when you start it after it has sat for awile?

Click to expand...

I forgot to check that. My wife drives it, so I'll have to check that one. What can that indicate?

not an expert by any means, but seems fairly normal to me...