There are three key areas of concern with ethanol compatibility with historic and classic vehicle fuel systems:
1. Corrosion of metal components
Ethanol has increased acidity, conductivity and inorganic chloride content when compared with conventional
petrol and can cause corrosion and tarnishing of metal components under certain conditions. These
characteristics are controlled in the ethanol used to blend E5 and E10 European and UK petrol by the ethanol
fuel specification BS EN15376 to help limit corrosion.
It is not clear if corrosion inhibitors are universally added to ethanol for E5 and E10 blending so, as an
additional precaution, it is recommended that aftermarket corrosion inhibitor additives are added to E5 and
Aftermarket ethanol corrosion inhibitor additives, often called ethanol compatibility additives, are usually
combined with a metallic valve recession additive (VSR) and sometimes an octane booster and have been
found to provide good protection against metal corrosion in historic and classic vehicle fuel systems.
2. Elastomer compatibility
As the ethanol molecule is smaller and more polar than conventional petrol components, there is a lower
energy barrier for ethanol to diffuse into elastomer materials. When exposed to petrol/ethanol blends these
materials will swell and soften, resulting in a weakening of the elastomer structure. On drying out they can
shrink and crack resulting in fuel leaks.
Some aftermarket ethanol compatibility additives claim complete protection for operating historic and classic
vehicles on E10 petrol. The FBHVC is not aware of or has tested any additives that claim complete fuel
system protection with respect to elastomer and gasket materials for use with E10 petrol. Therefore, the
FBHVC recommends that elastomer and gasket materials are replaced with ethanol compatible materials
before operation on E10 petrol.
3. Air/fuel ratio enleanment
Ethanol contains approximately 35% oxygen by weight and will therefore result in fuel mixture enleanment
when blended into petrol. 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, driveability issues (hesitations, flat
spots, stalling), but also could contribute to slightly hotter running. Adjusting mixture strength (enrichment) to
counter this problem is advised to maintain performance, driveability and protect the engine from overheating
and knocking at high loads.
Modern 3-way catalyst equipped vehicles do not require mixture adjustment to operate on E10 petrol
because they are equipped with oxygen (lambda) sensors that detect lean operation and the engine
management system automatically corrects the fuel mixture for optimum catalyst and vehicle operation.
Operating classic and historic vehicles on E10 petrol
If you should decide to run your historic vehicle on E10 petrol, the FBHVC strongly recommends that you
check the condition of the vehicle fuel system regularly for elastomer and gasket material deterioration and
metallic components such as fuel tanks, fuel lines and carburettors for corrosion.
Ethanol is a good solvent and can remove historic fuel system deposits from fuel tanks and lines and it is
advisable to check fuel filters regularly after the switch to E10 petrol as they may become blocked or
restricted. If your vehicle is to be laid up for an extended period of time, it is recommended that the E10 petrol
be replaced with ethanol free petrol which is available from some fuel suppliers. Do not leave fuel systems
dry, as this can result in corrosion and the shrinking and cracking of elastomers and gaskets as they dry out.
Concerns were expressed about the loss of low octane fuels with, in the view of some, “too much” octane for
old engines. Study has shown that this concern is baseless. In effect, it is impossible to have too much
octane quality, and older engines can operate very satisfactorily on a fuel with octane quality greatly
exceeding their natural requirement.
John Turley, FBHVC Rep