Ethanol
The Federation has identified three operational aspects relating to the addition of ethanol to petrol

Compatibility
Some elastomers, plastics and composite materials are not compatible with petrol containing ethanol

Corrosion
Long-term storage of petrol-ethanol mixtures (eg. over a winter period) can lead to corrosion in historic vehicle fuel systems. Following tests, a number of corrosion inhibitor additives which were effective at protecting fuel system metals were identified by the Federation and previously endorsed

Combustion
There is no evidence that the addition of ethanol to petrol directly affects combustion adversely, but ethanol does have a leaning effect; fuel mixture strength becomes slightly weaker, and this is particularly true for higher ethanol blends. Petrol containing 10% ethanol for example, would result in a mixture-leaning effect equivalent to approximately 2.6%, which may be felt as a power loss, but also could contribute to slightly hotter running, switching between ethanol containing petrol and non-ethanol containing petrol will result in the mixture in the fuel tank having a higher volatility, which may cause vapour locking problems and should be avoided if possible

The Federation therefore recommends that all vehicles produced before 2000 and some vehicles from the early 2000s that are considered non-compatible with E10 - should use the Super E5 Protection grade where the Ethanol content is limited to a maximum of 5%.