Is it harmful to mix 92 and 95 gasoline in a car?
2 Answers
Mixing 95 and 92 gasoline is harmful to the car. Occasionally using the wrong gasoline grade only requires switching back to the correct grade after use, but long-term use of the wrong gasoline grade can have the following effects: For vehicles recommended to use lower-grade gasoline, accidentally using higher-grade gasoline will not cause damage, but the increase in octane number will change the fuel's ignition point, leading to delayed combustion in the engine. This means the engine's power output and thermal efficiency will decrease, resulting in poorer performance. For vehicles recommended to use higher-grade gasoline, using lower-grade gasoline can cause engine knocking. Because the octane number is too low, the gasoline's ignition point decreases, causing it to ignite prematurely during the compression stroke. If the gasoline ignites before the spark plug fires during the compression stroke, resistance will occur during the upward stroke. This resistance makes the engine run very unstable. If the knocking is mild, it only increases noise and does not significantly damage the engine. However, if the knocking is severe, it indicates the engine's condition is very serious. The vibration not only affects driving stability but also causes abnormal wear on the pistons and cylinders, and in severe cases, can lead to cylinder scoring. In addition to checking the appropriate gasoline grade in the car's manual, you can also find it on the fuel tank cap. Usually, the gasoline grade can also be determined based on the engine's compression ratio. Cars with an engine compression ratio between 8.6-9.9 should use 92 gasoline, those between 10.0-11.5 should use 95 gasoline, and those with higher compression ratios should use 98 gasoline. However, with the use of new technologies, the compression ratio alone cannot determine the gasoline grade. Engines with high compression ratios can also be tuned to use lower-grade gasoline. Besides the compression ratio, other factors such as ignition timing, turbocharging technology, and Atkinson cycle technology also play a role. Generally, the higher the gasoline grade, the higher the octane number and the better the anti-knock performance. 92 gasoline contains 92% isooctane and 8% n-heptane, while 95 gasoline contains 95% isooctane and 5% n-heptane.
I've also researched the situation of mixing 92 and 95 gasoline. It mainly depends on what octane rating your car recommends. 92 has a slightly lower octane rating, while 95 is higher. A higher octane rating can prevent engine knocking under high temperature and pressure, avoiding engine damage. If the car requires 95 octane, mixing 92 might lower the overall octane rating, leading to incomplete combustion, knocking, or abnormal vibrations, which could damage the pistons over time. However, occasionally mixing once, such as half a tank of 92 and half of 95, with a low proportion, the engine's ECU control system will adjust the ignition timing to adapt to the fuel, and most of the time, it won't cause major issues. You can dilute it when the fuel runs low or during the next refill. It's recommended to use the specified octane rating as much as possible to maintain stable performance and avoid unnecessary repair costs. In short, don't stress too much about this. If you accidentally mix it once, don't worry—just drive for a while and observe if everything is fine. However, making it a habit could increase risks, affecting the car's lifespan and fuel efficiency.
