What happens if you fill a car designed for 92 octane with 95 octane gasoline?
2 Answers
If a car designed for 92 octane gasoline is filled with 95 octane gasoline for a long time, it may cause engine knocking, reduced power, increased water temperature, and metallic knocking sounds during operation. Gasoline is a mixture, and the octane rating refers to the anti-knock index of the gasoline. Strictly speaking, 92 octane and 95 octane gasoline should not be mixed. However, their chemical compositions are relatively similar, and both have strong anti-knock properties. Mixing lower octane gasoline with higher octane gasoline can lead to knocking, insufficient power, and may affect the lifespan of the spark plugs, as well as increase tailpipe emissions. Mixing different grades and types of gasoline may not cause obvious problems in the short term, but carbon buildup and fuel system blockages are long-term consequences of such mixing.
I also thought about this the last time I refueled. For a car that uses 92-octane fuel, filling up with 95-octane in the short term is definitely fine—the engine's computer will adjust the ignition timing to accommodate the higher octane. But doing this long-term is really unnecessary, as 95-octane fuel is significantly more expensive. Especially for older cars, higher octane can actually increase cylinder temperatures, which isn’t great for the gaskets. A friend who runs a repair shop mentioned they’ve seen several cases where long-term mixed fueling led to faster valve carbon buildup. Using it once in an emergency is fine, but it’s best not to make it a habit.
