Diesel engines use compression ignition — fuel ignites from the heat of highly compressed air alone, with no spark plug. Gasoline requires a spark to ignite and has a much lower flash point than diesel, meaning it can combust prematurely or unpredictably under diesel compression ratios, which typically run between 14:1 and 25:1.
The incompatibility goes beyond combustion chemistry. Diesel fuel also acts as a lubricant for the fuel pump and injectors. Gasoline lacks this lubricating property, so running it through a diesel system rapidly accelerates wear and can destroy high-pressure fuel components. A misfueling incident can result in thousands of dollars in repairs.
This technical reality became relevant when a viral March 2026 claim — traced by Snopes to the satire site Fazzler.com — falsely attributed to President Trump a suggestion that truckers switch from diesel to gasoline to cut fuel costs. Beyond being a fabricated quote, the suggestion would be mechanically impossible to act on without completely replacing the engine and drivetrain of a commercial truck.