So I have replaced the oil pressure gauge, sending unit, and oil pump, yet my oil pressure is still goofy as hell. Start up is fine, it's at about 45-50psi at idle, but after my 15 mile ride to work it's at around 10psi. Mobil1 fully synthetic is in the crankcase with a bosch filter. There's no knocking, pinging or loss of power, so I am perplexed. Yes the oil pump was primed, tried 3 different sending unit and gauge combos. It's a high volume oil pump, factory gauge and aftermarket sender.

 

bump

 

done a fuel oil drain?
Pour some clean oil in with the drain out as well to get rid of as much old and dirt as possible. Maybe you got some gunk that is on the bottom that gets picked up and does some clogging?

 

It sounds like you have done a good job of "confirming" your oil pressure.

So, unfortunately that means that you most likely have an excessive clearance in the engine bearings.

If sending unit, gauge, pump are all confirmed, that is the only real answer here............

You may want to drop the oil pan and use some plastigage to measure some bearing clearances here.

I will tell you this. I've worked on a lot of 4.0s and I have seen quite a few that run for a long, long, long time with a confirmed 10 psi of pressure.

When you get below that, it gets dicy.

Drive it and keep an eye on it. At this point, I would consider this oil pressure to be more of a "characteristic" of an older engine, rather than a problem that needs attention.

 

what weight Mobil 1 are you using? It's available from 0W-20 up to 15W-50

http://www.mobiloil.com/usa-english/...s/mobil_1.aspx

 

You have to watch out for high volume pumps sometimes. Some of them will pump so much oil that the pan doesn't hold enough oil to keep up. Luckily the XJs have a fairly big pan but some of them your not so lucky with.

 

10w30 is all I use. heavier weight oil often causes more problems than it's worth