Straight from the HGV drivers mouth

[OwlHoot]

Got a couple of big cans of gas oil, AKA red diesel, from my old heating system in my shed. Illegal to use though and not sure it it wouldn't damage me little van's engine.

Diesel and other high-energy fuels degrade over time.

Not sure what timescales that is, but probably after a year or two it will reduce by a few RONs and may be unusable.

edit: Here we are