I get the 5-qt Mobil 1 synthetic stuff from Wallyworld to do my oil changes, and leave just about half a quart each time when it's all done. After 3 or 4 times, I've accumulated quite a bit of never used oil. The problem is, parts of it (I pour the leftovers into the same container) may be 6~9 months old.
Is this oil still safe to use? It'd seem like such a waste just pouring it out, it's like $5 a quart!
I was thinking about using up the old stuff for my next oil change. What do you think?