Hey guys, I have been lurking around this forum and found a lot of informative posts! Thanks. Question I have, I have a 98 Jeep Wrangler with 4.0L I6 with 73k on it. It takes 6qts of 10w-30. I have been using Castrol GTX and Quaker State 4x4 Synthetic blend. Now I think it is time for some upgrade, what should I use? and why(for learning purpose)? Thanks, Michael K.