I have a 2001 Jeep Cherokee with a 4.0L inline 6. My oil pressure always read at 80 for over a year. That is the highest pressure it will read and then one day my jeep tripped out on me and my pressure reads anywhere from 40-60 driving. At idle it drops to 20-30 but the gadge starts off at 0 then goes to 40(middle) and ends at 80.