Can Different Grades of Gasoline Be Mixed?
3 Answers
92-octane gasoline and 95-octane gasoline cannot be mixed because they have different isooctane contents. 92-octane gasoline is suitable for engines with low compression ratios, while 95-octane gasoline is suitable for engines with high compression ratios. If 92-octane gasoline is added to a car that requires 95-octane gasoline, abnormal combustion may occur, leading to engine knocking. Knocking not only damages the combustion chamber but also directly affects the normal operation of the engine, and in severe cases, it may cause engine damage. If 95-octane gasoline is added to a car that requires 92-octane gasoline, although it will not damage the engine, 95-octane gasoline is more expensive than 92-octane gasoline, resulting in unnecessary costs. Differences between 92, 95, and 98-octane gasoline: Standard gasoline is composed of isooctane and n-heptane. Isooctane has good anti-knock properties, and its octane rating is set at 100; n-heptane has poor anti-knock properties and is prone to knocking in gasoline engines, so its octane rating is set at 0. If the gasoline is labeled as 92-octane, it means that the gasoline has the same anti-knock properties as standard gasoline containing 92% isooctane and 8% n-heptane. The same principle applies to 95 and 98-octane gasoline. What to do if the wrong gasoline is added: If a higher octane gasoline than required is added—for example, adding 95-octane gasoline when 92-octane is specified—simply use up the gasoline and then refill with 92-octane gasoline. If a lower octane gasoline than required is added—for example, adding 92-octane gasoline when 95-octane is specified—you can add a high anti-knock fuel additive. Alternatively, you can drain the gasoline and refill with 95-octane gasoline. To find out which gasoline grade your car requires, you can refer to the car's user manual or check the fuel grade labeled on the fuel tank cap.
When I ran a repair shop, I was often asked this question. Mixing 92 and 95 gasoline is completely fine for short-term emergencies, but don't do it long-term. The main issue is that different octane ratings have different anti-knock properties, and mixing them may cause engine knocking, especially in older cars or turbocharged models which are more sensitive. However, mixing when the tank is half full has less impact, as the ECU will adaptively adjust the ignition timing. I've seen people mix fuels for three years with no issues, but also cases where the check engine light came on after mixing—it really depends on the car's condition and driving habits. If you do mix fuels, don't panic; just switch back to the original octane rating at your next fill-up.
Just discussed this with my car-modifying buddies last week. Mixing gasoline octane ratings isn't forbidden—the key difference lies in their octane levels. Adding 92 to 95 is like diluting higher-octane fuel, potentially reducing knock resistance; mixing 95 with 92 might confuse the ECU's ignition timing. The real risk comes from frequently switching between high and low grades, forcing constant ECU recalibration that strains the engine. Our racing team's tests showed turbocharged cars exhibit more noticeable power lag than NA engines after mixing. In emergencies, half-tank mixtures are manageable, but performance cars should avoid it. Sticking to one consistent octane rating is always the safest bet.
