Oil - does it deteriorate?

[barryjwoo]

Hopefully an easy question, does semi-synthetic or synthetic oil deteriorate with age. I've some Mobil 1 in my garage that I reckon is about 6-7 years old. Should I use it or is the risk too high for the sake of saving a few quid?

[wildoliver]

Provided it isn't sat in an engine it will be fine, oil deteriorates when its been used as the ash content turns it acidic, plus all the other nasties your engine produces.

I've got oil older than that btw!

[zcacogp]

... sounds silly, but if it is in a metal tin, check that the tin hasn't rusted and dropped bits of debris into the oil. (Yes, it shouldn't happen, but I have seen it!)


Oli.

[willdew]

A mineral oil, almost by nature, doesn't degrade over time (being formed from decaying organic matter over hundreds of thousands of years). I presume the hydrocarbon chains in synthetic oils to be very stable, especially when sat in a bottle on a shelf (rather than at 140 degrees or whatever when in an engine).

Don't know what additives are might be in the oil that might break down, but my guess is even if there are some that aren't as good as they were when manufactured, they won't do any harm. Might just behave like a slightly less sophisticated oil.

[james_j]

I doubt it will deteriorate. However, maybe Mobil have a 'phone or e_Mail helpline.

[supermono]

Dear Mobil, I have some old oil should I use it or should I buy some more off you?

Ohhhhh, let me think

SM