I always keep a quart or two of oil in my trunk for "just in case" purposes. Currently, I have one sealed quart and one unsealed, half-used quart. Both Castrol 0w30 full synthetic.
I bought them both last year, they were in my trunk all (Canadian -30C) winter. Are they still okay to use for my next oil change?
Same question for a sealed (still in shrinkwrap) oil filter.
Unlike brake fluid, oil isn't hygroscopic (absorbs humidity) and is not capable of chemical dissolution with water, which produces new substances.
An added note: DOT 3 and DOT 4 are glycol based, which is hygroscopic; DOT 5 is silicone based, which is not hygroscopic. Hence why you should never mix the two, as it will become a kind of gel substance.
Sure, oil and water are capable of physical dissolution which is purely mechanical; an example would be shaking a bottle of Italian salad dressing. The different ingredients mix, but don't form a new substance.
You would be talking adding lot more water in the mix to even have any adverse affects (blown head gasket and such), than just a little bit of humidity which would most likely evaporate at running temperature anyway. And it would take a whole lot of water to have compression issues like hydrostatic lock and ruin your engine.
If it were me, I'd happily use what you've got for my next oil change.
