You may not realise it, but fuel ‘goes off’. Some fuels expire faster than others. Many of you will have experienced or heard of cars refusing to start after being left motionless for long periods of time. In most cases, this is because octane levels in the old fuel have dramatically dropped.
Generally speaking, due to the evaporation of the chemicals used in them, higher octane fuels lose their potency faster than lower octane fuels. Even premium unleaded pump gas is said to be past its best if left in a car’s fuel cell for more than a fortnight!
When dealing with an engine operating near its detonation threshold, running old fuel can be a serious problem, so try not to leave petrol in hibernating cars.