I am running 20W-50 in my Jimmy right now. I run it in the AZ summers. I haven't run it very long yet. I just started running it on suggestion by DesertDueler. I listened to all the arguements on running heavy oil, but in the AZ heat, I figured that 20W-50 wouldn't be bad for the motor at all, and might last longer between changes. Right now I change oil about every 2K in the summer with 10W-30. Maybe I will get 2.5K now.