The Effect of the Addition of Ethanol to Petrol

At the recent club meeting Peter Crowther commented on the addition of

Ethanol to petrol and the effects on seals and hoses in the bikes fuel systems

particularly during periods of storage or lay up as over the winter period.

A campaign document prepared by MAG,, gives a comprehensive summary of the

background to the reason for the addition of ethanol to petrol and the

corrosive effects on materials used in the fuel systems.

The greater solvent effects of ethanol and the higher capacity to absorb

moisture make petrol containing ethanol more corrosive, loosening abrasive

deposits and leading to increased wear and fuel system blockages.

Material incompatibility with Ethanol can result in, swelling, softening and

embrittlement of materials leading to reduced structural integrity. In some

cases failure of sealants, hoses and glass fibre components have led to

catastrophic leaks in fuel systems and failure of petrol tanks.

Ethanol contains more oxygen than petrol so that the air/fuel balance is

altered leading to a lean mix and problems with overheating and driveability

problems. The problems will obviously increase with additions upto 10%


Modern engines have been developed to cope with Ethanol but the effect on

older ‘vintage’ bikes is causing considerable concern. [Don’t forget your lawn

mower and garden equipment!]

Premium 95 unleaded grades contain a maximum of 5% Ethanol, but there

are plans for this to be increased to a maximum of 10%. Currently, most

Super 98 unleaded such as BP Ultimate has no Ethanol added, so that

provides an alternative for winter use. [apparently it is difficult to maintain the

performance with added Ethanol!]. There are some regional variations particularly in the South West and North West.

The standard for petrol with added Ethanol is En228 E5 and E10 but there is no requirement for pumps to be labelled.

Changes are planned so watch this space.

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