With many months between changes at the 10,000 mile interval, and the fact that it takes 4.5 quarts, I called Mobil to see what the shelf life is on an opened quart. I was told it is 1 year. He also said, you can pour it into a glass jar before use and if it is separated like vinegar and water, don't use it. He also said storing it in a climate controlled area like a basement rather than the garage would extend the shelf life.
Wow interesting. Suprising answers. Given we are talking about a synthetic oil that is designed to protect your engine and exist in the internal operating enviroment of a functioning engine, I find it suprising that an untouched opened quart could separate like vinegar and water and be so strongly affected by such enviromental differences as basement or garage. I mean it goes into your engine and potentially from very low tempatures to very high tempatures and yet storing it opened and untouched in your garage could cause it to separate? Those were not answers I'd expect.
I also am surprised to hear this. If true, I am surprised that 1) there is no date code on the bottle and 2) there is no warning advising the user to use or recycle the contents within one year after opening the bottle.
I was also surprised that it is this short. I remember asking Castrol the shelf of an unopened quart of "real" oil as I have in my garage for my generator and I think they said 4-5 years. The guy from Mobil that I spoke to today gave the answers right away without looking anything up, or he made it up. Maybe a 2nd call with the same questions would be interesting.
I have a few cans of Valvoline 20W50 oil stored in my garage for 25+ years, which I opened a can of it a few months ago. it still looks like brand new oil, no separation like OP described which I never heard of.
Mobil says 5 years for unopened Mobil 1 Shelf Life of Unopened Mobil 1 Quarts I suspect that is a very conservative answer, it will probably last several times that long if stored between 45 and 80 degrees F (temperatures from Amsoil site). I would think an open container that is kept clean and recapped right away would last just as long. If in doubt shake before use.
I remember my auto shop teacher in high school told us that gasoline turns into gel after a few decades of storage.
I just emailed them the same question that I asked on the phone so we will see if I get the same answer.
I don't buy it. First of all, the oil may already be significantly old by the time its put into the car. Oil is not "sealed", its in a bottle but its not a sealer bottle like would be used for some food item. As long as its capped...an opened bottle of oil should last as long as an unopened bottle...