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.

  • As long as you will live. Google says 5 years but I think that is BS.
    – Moab
    Commented Apr 18, 2018 at 19:57
  • I'm really not sure about the oil, but the filter, as long as it stays dry and wrapped, will last indefinitely. Commented Apr 18, 2018 at 21:31

1 Answer 1


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.


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