Will mixing 95-octane gasoline with a car designed for 92-octane have any impact?
2 Answers
According to the "Motor Vehicle Gasoline" (GB17930-2016), using 95-octane gasoline in a car designed for 92-octane does have an impact. Long-term mixing of different octane ratings will affect the service life of the car's ignition system, fuel injectors, and spark plugs, leading to an earlier need for major repairs. The appropriate gasoline grade can be determined based on the engine's compression ratio. Cars with an engine compression ratio between 8.6-9.9 should use 92-octane gasoline, while those with a compression ratio between 10.0-11.5 should use 95-octane gasoline. If the compression ratio is even higher, 98-octane gasoline is recommended. However, with the application of new technologies, the compression ratio alone cannot determine the required gasoline grade. High compression ratio engines can be tuned to use lower-octane gasoline because other factors, such as ignition timing, turbocharging technology, and Atkinson cycle technology, also play a role. Generally, the higher the gasoline octane rating, the higher the octane number 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. According to "Motor Vehicle Gasoline" (GB17930-2016), occasional use of the wrong gasoline grade only requires switching back to the correct grade after consumption. However, long-term use of the wrong gasoline grade can have the following effects: Using a higher-octane gasoline in a car designed for a lower octane rating will not cause damage, but the increased octane number may alter the fuel's ignition point, leading to delayed combustion in the engine. This reduces the engine's power output and thermal efficiency, resulting in poorer performance. Using a lower-octane gasoline in a car designed for a higher octane rating can cause engine knocking. The significantly lower octane number reduces the fuel's ignition point, causing premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance is created during the upward stroke, making the engine run very unstably. Mild knocking may only increase noise without obvious engine damage, but severe knocking indicates serious engine conditions, affecting driving stability and causing abnormal wear on pistons and cylinders, potentially leading to severe damage like cylinder scoring. Notes on gasoline selection: Choose gasoline with appropriate volatility based on the car's operating temperature. Gasoline with good volatility facilitates cold starts and ensures smooth engine warm-up. However, excessive volatility can easily cause vapor lock in the fuel lines, preventing the fuel pump from delivering gasoline properly and leading to engine stalling. Select gasoline based on its lead content.
I've found that mixing 92 and 95 octane gasoline in regular family cars isn't really a big issue. My car usually runs on 92 octane, but when the gas station only has 95 octane, I'll mix some in. The engine still runs smoothly without any noticeable problems. Having driven for ten years, occasional mixing doesn't harm the engine because higher-octane fuel just burns more stably and won't cause any car troubles. However, frequent mixing is a bit of a waste of money since 95 octane is more expensive without improving the car's performance. I recommend sticking with 92 octane for daily use—it's economical and worry-free. If you're really concerned, try taking a long drive after refueling or regularly maintain and check the fuel filter to prevent impurities from causing issues. In short, this isn't a major problem, so drive with peace of mind!
