Is There Any Problem with Mixing 95 and 98 Octane Gasoline?

[Sadie]

Mixing 95 and 98 octane gasoline is problematic. If you occasionally fill up with the wrong gasoline grade, simply switch back to the correct one after using it up. However, long-term use of the wrong gasoline grade can have the following effects: For vehicles designed for lower octane gasoline, using a higher octane grade will not cause damage, but the increase in octane rating can alter the fuel's ignition point, leading to delayed combustion in the engine. This results in reduced engine power and thermal efficiency, with the actual driving experience being poorer performance. For vehicles designed for higher octane gasoline, using a lower octane grade can cause engine knocking. Because the octane rating is too low, the gasoline's ignition point decreases, causing it to ignite prematurely during the compression stroke. If combustion occurs before the spark plug fires during the compression stroke, resistance will arise during the upward stroke. This resistance makes the engine run very unevenly. If the knocking is mild, it may only increase noise without significant engine damage. However, noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, and in severe cases, cylinder scoring. In addition to checking the recommended gasoline grade in the car's manual, you can also find it on the fuel tank cap. Typically, the gasoline grade can also be determined based on the engine's compression ratio. Cars with a compression ratio between 8.6-9.9 should use 92 octane gasoline, those between 10.0-11.5 should use 95 octane, and those with higher compression ratios should use 98 octane. However, with the use of new technologies, the compression ratio alone cannot determine the appropriate gasoline grade. High-compression engines can also be tuned to use lower octane gasoline due to other influencing factors, such as ignition timing, turbocharging technology, and Atkinson cycle technology. Generally, the higher the gasoline grade, the higher the octane rating and the better the anti-knock performance. 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane.

[MacLaila]

I've driven several cars before and occasionally mixed fuel grades, like adding 95 and 98 together. From my experience, it's generally not a big issue. Modern engines have automatic adjustment functions that can adapt to octane variations. Mixing fuel results in an average octane rating within a mid-range, which may reduce knock risk and won't immediately damage the engine. However, each vehicle is designed differently. If your car recommends high-octane 98 fuel, forcibly mixing grades might lead to performance degradation or increased fuel consumption. I remember one instance when mixing caused slight engine vibration, but it didn't last. For occasional cost-saving, mixing once is acceptable, but habitual long-term practice may accumulate carbon deposit issues, affecting long-term engine health. I recommend consulting the manual to choose a single fuel grade, unless mixing temporarily in emergencies. This ensures more confident driving and avoids maintenance headaches.

[Matilda]

Speaking of mixing 95 and 98 gasoline, I think it's technically acceptable from an engineering perspective. The octane rating difference is key - 95 has weaker knock resistance while 98 is stronger, and mixing them yields a median value. The engine can automatically adjust ignition timing to compensate. During my car testing, I found mixed fuel has minimal impact on daily driving, with no noticeable changes in noise or power output. However, be cautious: if a vehicle specifies 98 as the minimum requirement, mixing with lower-grade 95 may cause combustion instability or fuel wastage. While cost-saving, mixed fuel doesn't improve efficiency and sometimes isn't worth it. I recommend only mixing within manufacturer specifications to maintain consistency and avoid sensor errors. Engine maintenance relies on stable fuel quality - don't recklessly push limits.

[LeHarrison]

I'm quite concerned about the economic aspect of mixing 95 and 98 gasoline. 98 is more expensive but efficient, while adding some 95 can save money in the short term without issues. The engine adapts to octane variations, with possible minor combustion changes but no damage. However, mixed fuel may not be as efficient or fuel-saving as a single type—for example, insufficient power at high speeds might require more throttle, costing more. I've seen fuel-saving enthusiasts mix long-term, only to end up with higher consumption and engine repairs. If your vehicle doesn't demand high octane, occasional mixing is fine to cut costs, but ensure the octane doesn't drop below recommended levels. Monitor your fuel gauge for actual effects, balancing wallet and vehicle health.