It was time to change the oil in my Jeep today. I went to Autozone on the way home from work and got 6qts of Mobil 1 and a filter, but when I looked at the shelf-of-partial-bottles-of-oil in the garage, I saw several 5w-20 bottles in there.
I opted to use the old bottles. The color startled me a little bit in them though. Instead of a conventional amber, they had shifted to red a little bit. I ended up using 1qt of brand new oil but the rest was this older red shifted Mobil 1. They'd been sitting in my Arizona garage for a couple of summers at this point... I'm long between oil changes since I ride a motorcycle most of the time. I'd guess the bottles were between 12 and 18 months old.
Anyone ever seen that? Jeep seems to run fine. I think this will end up being a short oil cycle with this oil just to appease any concerns I have with the quality of older oil.
I ended up returning my 5qt jug of new Mobil 1 for a refund since I didn't want it to sit in my garage for a long time and turn dubious like the last batch.