Does motor oil ever expire?
 

It may be somewhat of a noob question, but I've been wondering for quite some time now. Does engine oil, full synthetic to be precise, ever expire? If so, how long should it last? I have some left over from a few oil changes over the years and was wondering if its advisable to still use it.

it probably does. or at least has a "best by" date... but dont know to be honest....

If unopened, stored inside it can last a few years. The thing to look for is water being absorbed while its sitting. If its opened, its about 6 months to a year.

You can still use full synthetic left overs that are a few years old, as long as you kept it in a garage where too much moisture couldn't get at it. Synthetic oil never breaks down like dyno oil does, so as long as it doesn't get contaminated (hasn't been opened) it should in theory, last forever.

it doesn't really go bad. one thing you can do it cook it i guess lol. try mixing it with some you just bought.

Problem is, it HAS been opened. I have a 4 quart jug full of synthetic oil change leftovers. It's left over 15w 50 from my old Civic. Been saving it up for a couple years. So chances are it's not a good idea to use?

well like i said you can heat it up so most of the water evaporates and then it would be safe to use. also you should be able to see the water as oil and water are not soluble. i believe water should be on top, been a while since chemistry lol

Oil floats..

Heat it up? Like in a cooking pot? If I shake it up real well I should be able to see the water if it's there, right?

Just buy new oil. You dont want to risk anything. I dont think anything would actually happen, but its better safe then sorry.