I have almost 5 quarts of left over oil mixed in a container. My car takes 4.5 quarts and I always dump the other half quart into a container. Now it's almost full. It's all M1 with a mix of 5w30 and 10w30 and has been sitting there for a couple years now since I change every 6 months. Would it be ok to use this oil the next time with it being mixed and for how long it has been sitting there?