Can You Add 95 Octane Gasoline After Using 98 Octane?
3 Answers
You cannot add 95 octane gasoline after using 98 octane gasoline. Here are some relevant details about gasoline: Characteristics of gasoline: Gasoline has properties such as volatility, stability, anti-knock quality, corrosiveness, and cleanliness. Engines with high compression ratios should use high-octane gasoline. If a high-compression engine uses low-octane gasoline, it can cause abnormal combustion, leading to knocking and reduced driving power. Hazards of mixing gasoline: Mixing different octane levels can disrupt normal engine operation, leading to increased noise, reduced driving power, and potential engine damage. Different gasoline octane ratings indicate varying levels of anti-knock performance—the higher the octane number, the better the anti-knock performance. Gasoline is a volatile, flammable hydrocarbon mixture liquid derived from petroleum through distillation, cracking, or pyrolysis, and is used as fuel.
I usually drive high-performance cars and always use 98-octane fuel. That time when the tank was almost empty, I could only find 95-octane at the gas station. I consulted the manufacturer's engineer, who said mixing once is not a big problem as the engine computer will adjust the ignition timing to avoid knocking. However, long-term mixing is not good for the engine, especially for turbocharged cars where pressing the throttle at low RPMs can easily produce metallic knocking sounds. It's recommended to switch back to 98-octane next time, and if it's an emergency, don't exceed one-quarter of the total fuel volume. Actually, choosing fuel mainly depends on the vehicle manual—my car's fuel cap clearly states that 98-octane should be used.
Just helped a friend deal with a mixed fuel issue a couple of days ago. His Porsche was supposed to use 98 octane, but he accidentally filled it with 95. The diagnostic computer showed the knock sensor working overtime to compensate ignition timing, with short-term fuel consumption increasing by 15%. Fortunately, no warning light came on. Different octane grades have significantly varying additive formulations, and the mixed octane rating isn't a simple average. It's advised that high-octane vehicle owners avoid fuel mixing whenever possible - engine knock during hill climbs or sudden acceleration could be dangerous.
