Its not an exact science as it depends on conditions but after 12 months its considerably deteriorated.Will it be no good whatsoever then?
I am sure you will find some tight bleeder to give it a go.... the army keep it for longer... I have used stuff 2 years old in the landrover, I think the knowledge of Diesel and longevity has only recently came to light.Oh well. If nobody here wants it then it's safe to say nobody anywhere wants it
Never realised it would go off.