Originally Posted By: ChrisD46
For Lex94 & others - I'm assuming from your comments that the 10W30 Penzoil HM oil is more sheer stable in higher temps then say the 5W30 with more VI's added ? To date , I just never bothered to try a 5W30 HM oil in the 4.0L yet - perhaps others have and it worked fine ... I just stayed with what the old 1995 OM suggested which was 10W30 .
I've run HM 5w30's and they work/run great, as long as you stay with the thicker ones like Defy, PHM or Castrol.
I tried regular 5w30 (Castrol) in my old Jeep and it sounded like a brass band, I drained it out and went back to regular 10w30 problem solved. This Jeep the only standard 5w30 I've run is PYB and it runs great but I only do that in the winter months.