What is the primary cause of driveability problems when alcohol is mixed with gasoline?

The primary cause of driveability problems when alcohol is mixed with gasoline is excessive amounts of alcohol degrading fuel system components. Alcohols, such as ethanol or methanol, can be corrosive and may cause degradation of certain materials used in fuel system components, including rubber seals, gaskets, and plastics. This degradation can lead to fuel leaks, blockages, or increased wear on components, ultimately impacting engine performance and driveability.

While alcohol can increase the octane rating, which is considered beneficial for performance, the degradation of fuel system parts has a more direct and serious impact on how the vehicle operates. Similarly, improved carbon monoxide emissions due to alcohol blending are not a direct cause of driveability problems; instead, they may be seen as an environmental benefit. Lastly, while compatibility with vehicle fuel systems is an important consideration, the excessive degradation of materials from alcohol exposure is a more significant issue that directly affects the vehicle's performance and reliability.