Old oil
 

I recently found a 4 litre container of un opened Rock oil 10/40 semi synthetic in the garage, its a few years old. Do you all think it will be OK to use?

old oil
 

Shake it to the right, shake it to the left - and pour it in.
Oil is essentially millions of years old, and although it might separate in layers it is still usable. Heat can cause some molecular breakdown, but I assume you don't have a nuclear reactor in your garage.
Best of luck, just think how much your four liters has appreciated compared to bank interest rates!
Peter, in Oslo

Yes, as long as it is sealed !!!

Liquid gold... It's like finding £30 in an old coat pocket :D