Had a shop replace my rear main seal recently.

My oil pressure before the replacement was always 60lbs cold, 50lbs hot.

After the replacement my oil pressure is now 20lbs.

What happened?

 

You could coincidentally be having a problem with the oil pressure sending unit. It is located directly above the oil filter. It is not at all uncommon for them to fail.

I'm not saying that is what your problem is but it is the first thing I would rule in or out. You have two options. Temporarily install a "mechanical" oil pressure gauge where that sending unit resides and then you'll know for sure what your oil pressure is. This is what a shop technician would likely do. Or roll the dice and install a new genuine Mopar oil pressure sending unit and hope that resolves it. Your dash oil pressure gauge itself is also in play here, but the sending unit fails way more often.

The oil pressure spec for the 4.0 is as follows:

*Between 37-75 psi OVER 1600 rpms
*Not less than 13 psi at HOT idle

Good luck and keep us updated!

 

What oil did they use ? if they used a 0w-20 you would have low oil pressure .

 

It was 10w-30 oil and the oil pressure gauge is confirmed accurate.

The reason why I asked this question is because shortly after replacing the RMS and getting low oil pressure the connecting rod bearing on cyl #2 fried and wore out the crankshaft.

I suspect that they did something when replacing the RMS that caused the low oil pressure and resulting damage.

Would incorrectly installing the RMS cause a failure of oil delivery to the bearings?

 

It wouldn't have to be just a RMS that would cause other issues. Internally, if you have lower than required oil pressure, you're not going to get oil up/to all of the critical components and that will give you issues. Are there any leaks that there weren't before the RMS change?
Also, have you already discussed this issue with the shop that you had do the work? What were their thoughts?

 

To me it sounds like they forgot to put oil in it after they swapped the seal and then fired it up.

 

X2

 

Sounds suspiciously like they ran it dry and fried the bearing. I'm with 5-Speed on this...