fuels damaging rubber components?
Following the release of a note
setting out his concern
that modern fuels containing bio ethanol appear to be attacking the
rubber components in the carburetters and fuel pumps of our MGs,
Barrie Jones has provided the briefing note below with useful
background information and reports of known problems on this
of known problems
Details of all known problems from either publicly available technical
sources or from the comments and views sent in by members of the T
and V8 Registers and other Club members will be published on this
Last update: 11.1.08
Ethanol in Petrol
Ethanol is also known as Ethyl Alcohol and petrol containing
10% Ethanol is commonly referred to within the industry as
an E10 blend.
On 10th November 2005 Alistair Darling announced that the
UK Government's main support for biofuels will come in the
form of a Renewable Transport Fuels Obligation (RTFO) which
requires all transport fuel suppliers to ensure that, by 2010,
5% of their total aggregate fuel sales is made up of biofuels.
Octane Rating Increase
The octane rating of a petrol fuel is defined as a measure
of the resistance of the fuel to abnormal combustion - known
as "knocking". The higher the octane rating, then
the less likely it becomes that the engine will be susceptible
to "knock". By adding 10% ethanol to petrol (E10),
we can increase the octane rating of the petrol fuel by two
points. Therefore bio-ethanol is classed as an "octane
Air Fuel Ratio
The air/fuel mixing ratio that is required for 100% petrol
in order to achieve complete combustion is about 14.6 parts
of air to 1 of fuel by weight. This means that 14.6 Kg of
air is required for the complete combustion of 1 Kg of non-oxygenated
An ethanol E10 blend of fuel will normally have an oxygen
content of about 3.5% oxygen. Therefore, it is usually necessary
for car engines to have the air/fuel ratio reduced in order
to take into account the oxygen that is present in the ethanol
blend. The air/fuel ratio for a VW Golf running on 22% ethanol
is 12.7:1, which is significantly less than the 14.6:1 air
/ fuel ratio that is used for conventional fuels.
The engine management systems that are fitted to most modern
motor vehicles will electronically sense and change the air/fuel
mixing ratio in order to maintain the correct mixture when
ethanol (oxygenated) fuels are used. In most current vehicles,
the maximum oxygen content that the system can compensate
for is 3.5% oxygen (i.e. E10 ethanol fuel blends).
Older vehicles with carburettors are not normally fitted with
engine management systems. In such cases the carburettor air/fuel
mixture will have to be adjusted manually in order to compensate
for the increased oxygen content that is present in ethanol
. . .
Engine Modifications for Ethanol blends of 14% to 24%
The following engine modifications were found to be necessary
by car companies in Brazil in the 1970s, when vehicles were
operating on E20, a blend of between 14% and 24% ethanol:
> Changes to cylinder walls, cylinder heads, valves
and valve seats.
> Changes to pistons, piston rings, intake manifolds
> Nickel plating of steel fuel lines and fuel tanks
to prevent ethanol E20 corrosion.
> Higher flow rate fuel injectors to compensate
for oxygenate qualities of ethanol.
Vehicle owners running their cars on ethanol blends should
adhere to the recommendations of the individual car manufacturers.
In the UK, nearly all vehicle manufacturers specify that the
maximum ethanol blend in petrol should be no more than 5%
ethanol by volume. In the USA, nearly all vehicle manufacturers
specify that the maximum ethanol blend in petrol should be
no more than 10% ethanol by volume. Therefore, should a vehicle
owner choose to use a higher ethanol blend that the manufacturer
recommends, then normally the vehicle's warranty would become
null and void. Most vehicle manufacturers also state that
vehicle damage and driveability problems would occur by using
higher ethanol blends that those recommended by the manufacturers.
Ethanol blends have a higher latent heat of evaporation than
100% petrol and thus ethanol blends have a poorer cold start
ability in Winter. Some vehicles may require a small petrol
tank to be fitted containing 100% petrol just to start the
vehicle in cold weather.
Rubber and Plastic
For the past few decades automotive fuel system plastics and
rubber have been designed to tolerate up to 10% ethanol (E10)
without problem. In very old engines Ethanol may degrade some
compositions of plastic or rubber fuel delivery components
designed for conventional petrol.
It may be necessary to change the fuel filters more often,
as ethanol blends can loosen solid deposits that are present
in vehicle fuel tanks and fuel lines.