Why ethanol blended petrol is not recommended for use in some older vehicles
The following information outlines the key reasons why vehicle manufacturers do not recommend the use of any ethanol/petrol blended fuels in vehicles made before 1986. This information is also applicable to post-1986 vehicles listed as unsuitable to use ethanol blended petrol.
Ethanol has a number of important chemical and physical properties that need to be considered in a vehicle’s design.
Carburettor Equipped Engines
Vehicles made before 1986 vehicles were predominantly equipped with carburettors and steel fuel tanks.
The use of ethanol blended petrol in engines impacts the air/fuel ratio because of the additional oxygen molecules within the ethanol’s chemical structure.
Vehicles with carburettor fuel systems may experience hot fuel handling concerns. This is because the vapour pressure of fuel with ethanol will be greater (if the base fuel is not chemically adjusted) and probability of vapour lock or hot restartability problems will be increased.
As a solvent, ethanol attacks both the metallic and rubber based fuels lines, and other fuel system components.
Ethanol also has an affinity to water that can result in corrosion of fuel tanks and fuel lines. Rust resulting from this corrosion can ultimately block the fuel supply rendering the engine inoperable. Water in the fuel system can also result in the engine hesitating and running roughly.
Fuel Injected Engines
In addition to the issues mentioned above for carburettor equipped engines, the use of ethanol blended petrol in fuel injection systems will result in early deterioration of components such as injector seals, delivery pipes, and fuel pump and regulator.
Mechanical fuel injection systems and earlier electronic systems may not be able to fully compensate for the lean-out effect of ethanol blended petrol, resulting in hesitation or flat-spots during acceleration.
Difficulty in starting and engine hesitation after cold start can also result.
Exhaust And Evaporative Emission Levels
Lean-out resulting from the oxygenating effect of ethanol in the fuel may affect exhaust emissions.
Of more concern is that fuel containing ethanol can increase permeation emissions from fuel system components, particularly those that have aged for nearly 20 years. Therefore the increased vapour pressure of fuel with ethanol (if the base fuel is not chemically adjusted at the refining stage) will lead to increased evaporative emissions.