I have a 1997 with the 4.0. It has 196000 miles on it. I am using 10w30 synthetic oil.
When I first start it, the oil pressure is about 50 psi. When I start driving, it is about 45 psi. After about 15 minutes, it will drop to 20 psi and fluctuate between 15 and 30 psi.This is at about 1900 rpm...