I have an 04 Wrangler with the classic inline 6. I have learned a ton from this website and I can say since I started changing my own oil I have seen an increase in its performance. My mechanic who changed the oil previously would put 10w40 assuming it was better, I am currently running QS Defy 10w30 and I definitely noticed a quieter engine once warm and definitely more power when I hit the gas pedal. I want a high mileage oil in 5w30 and here's why: After a bunch of research I realized 10w30 Defy oil has a significant higher viscosity then non high mileage oils. In fact both M1 High Mileage and QS Defy in 5w30 are still more viscous than a fully synthetic 10w30 (PP for example) with that being said I want to try 5w30 QS Defy or M1 HM (even though manual says 10w30) as I want easier cold start up since it's been quieter on thinner oil when hot so maybe it'll like it thinner cold too. Reason for wanting high mileage is mostly because I want to prevent any leaks I know this engine is nearly indestructible but I want to keep it happy and healthy and all I can see going wrong in the future is a leak so I think a HM oil can help prevent this. I am a SOPUS guy (my dad has a strong fleet with history on rotella)(no im not going to put T6 in, its too thick) but am considering M1 HM as I think it probably has more detergents and is fully synthetic? Rather than semi like Defy. When should I change my oil and filter? I am definitely a "severe condition" as over 90% of my driving is frequent short trips and stop and go traffic (city driving with occasional short trips on the highway). It is basically a weekend warrior so it will sit for days before it goes anywhere and I only put about 4000 miles on it per year. Should I change my oil every 6 Months or Every year? I'm thinking maybe 6 moths if I go with Defy or a year if I go with M1 High Mileage or stick to 6 Months regardless? For a filter I have seen great things on the royal purple filters ($11 on amazon) and want to give it a try. If I do decide to change my oil every 6 Months could I change the filter just once a year? (Every other) I don't really see why not since it's supposed to last longer and filter better than the standard filter plus I thought maybe a high end filter once a year is better than a cheapo paper filter every 6 Months and would make up for the cost. Thoughts? Opinions? Suggestions?