Can 95 and 98 Octane Gasoline Be Mixed?
3 Answers
95 octane and 98 octane gasoline should not be mixed. Here are the specific details about car refueling: 1. Gasoline grade explanation: Although 98 octane gasoline has higher anti-knock performance and power, vehicles designed for lower octane fuel should not blindly use higher octane gasoline. Higher octane numbers are more suitable for engines with larger compression ratios, while engines designed for 95 octane often have smaller compression ratios. Using 98 octane gasoline may increase engine knocking. 2. Avoid mixing: Different octane grades of gasoline should not be mixed, such as mixing 98 and 95 octane gasoline. Long-term use of mixed gasoline may have certain effects on the engine, including engine carbon deposits and increased fuel consumption.
I've been driving for over twenty years and have mixed 95 and 98 octane gasoline many times, usually in emergencies. The car won't break down immediately, but it depends on your car model. For family cars like Toyota and Volkswagen, which have lower compression ratios, mixing results in an octane rating around 96, and there's basically no difference in driving performance, though acceleration might feel a bit softer. However, long-term mixing can lead to engine knocking and faster wear, making repairs not worth it. I specifically asked a mechanic, and he said the ECU can adaptively adjust ignition timing, but don't make it a habit, especially during winter startups, as the impact is greater. Safety first—the fuel cap manual specifies 95 octane, so I try to stick to it to avoid severe engine shaking someday. If you do mix, driving one or two tanks won't cause issues, but switch back as soon as possible and regularly check spark plugs to prevent problems. Don't save a little money only to cause bigger trouble.
From a technical perspective, I've experimented with fuel mixing several times and monitored the data using an OBD scanner. 95-octane fuel has lower octane rating and poorer anti-knock performance, while 98-octane is higher. When mixed, the average comes out to about 96.5, which is theoretically sufficient for regular engines. However, for high-compression engines like BMW turbo models, mixing may reduce performance. Although the ECU can compensate, there's millisecond-level delay, increasing the risk of micro-knocking during acceleration. When I mixed half a tank, fuel consumption slightly increased by 5%, and CO2 emissions were also higher, which isn't ideal environmentally. It's acceptable for short-term emergencies but not recommended for long-term use. Always check the manual—if the engine is designed for 95-octane, don't arbitrarily upgrade. As for fuel pump contamination during mixing? Rare, but minor fuel quality variations have little impact. To be safe, I never mix higher-octane fuel when using 95.
