Classic Etha-Guard Plus from Castrol is a fuel additive designed to stabilise the Ethanol content found in E5 and E10 unleaded fuels. It offers the best protection against the damaging effects Ethanol can cause to older petrol powered vehicles.Protects against the damaging effects of Ethanol found in modern unleaded petrolIdeal for modern classics from the 80's and 90'sCompatible with catalytic convertersProtects fuel systems while vehicles are in use and also while in storageCan increase performance and fuel economy1 Bottle treats up to 250 litres of fuelCastrol Classic Etha-Guard works by counteracting Ethanols hygroscopic nature. Hygroscopic means it holds water which can then cause corrosion within the fuel system. Etha-Guard prevents this from happening even when if the vehicle is in storage. It also prevents acidity caused by Ethanol which can attack rubber fuel lines and other rubber fuel components such as carburettor or fuel pump seals.Classic Etha-Guard also includes an 'Opti