i had some pennzoil (unopened) sitting in a warm garage for a couple years and used it on the last oil change. it was the same stuff as the stuff i bought the other day as far as container style and labeling. i was curious to know whether oil breaks down with time, heat, light, etc and the effects of using old oil. anyway, i finished pouring in the "old" stuff and there was sort of a black line of "dirt" resting on the bottom of the container. i shook it up before even opening it and it was still there but it otherwise looked ok. thoughts? thanks
