• I have a 99 xj 4.0 with 275k miles lifted on 35's, just got for cheap. Runs perfect with no noises. At cold start oil pressure is 45 psi. Great! However, at hot idle after about twenty mins when finally warm she reads 15 psi. When warm at 1.6k rpms she reads right about 35 psi plus or minus a hair or two. Oil Psi verified with manual guage. Replaced sending unit with mopar unit.Running 20w50 oil with Motorcraft filter.
• Just in case somehow related also have no ac or heat. Added freon, compress turns on, then psi drops and compressor clutch stops. Hot cold switch only works full blast not on low or medium fan. Heater lines not getting hot.
• Main concern is oil pressure. I know its right about at spec. Can I run her like this? Runs perfect. Thx in advance.

 

That's how mine runs.

 

I"d call that a hair low with 20w50, but not low enough to freak out about. Slightly related I've been running 20w50 and 10w40 mix about half and half in my Subaru for 50,000 miles. Pressure is the same as yours, but it hasn't dropped at all during that time even though I drive it like a race car all the time. I was worried at first, now I'm not. FWIW.