Modern 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 topic.
Reports 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 webpage.

Last update: 11.1.08
Briefing Note
Bio 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.

UK
Government Policy
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 enhancer".

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 petrol fuel.

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).

Carburetters
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 blended fuels.
continued . . .

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 and carburettors.
> 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 Warranties
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.

Cold Starting
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.

Fuel Filters
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.

Posted: 11.1.08

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