Oil life?? Time vs. mileage ....

Any more it is not cheap insurance. Jiffy lube, cheap yes! But crappy oil with low dollar filter. Mobile 1 is not cheap by any standards. 2001 Dakota R/T I bought new and still drive. Changed intake manifold and was blown away inside of engine was brown. (58000 miles) No sludge, but my point is every person here is consistent with contaminents after oil is poured in. I compromise with 4000 mile oil changes and it is still working good so far. My 2 cents, I think there is a ton of good advice here. Thanks to all with sharing!