Can 95 Gasoline Be Mixed with 98 Gasoline?

[AlinaFitz]

Occasionally mixing 95-octane gasoline with 98-octane gasoline is acceptable, but long-term use of different octane ratings can affect the car's engine, leading to delayed combustion. This means the engine's power output and thermal efficiency will both decrease, resulting in poorer performance and potentially advancing the vehicle's major maintenance schedule. You can choose the appropriate gasoline grade based on the engine's compression ratio. Cars with an engine compression ratio between 10.0 and 11.5 should use 95-octane gasoline, while those with a higher compression ratio should opt for 98-octane gasoline. However, with the application of new technologies, the compression ratio alone cannot determine the suitable gasoline grade. Engines with high compression ratios can also be tuned to use lower-octane gasoline, as factors like 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. 98-octane gasoline contains 98% isooctane and 2% n-heptane, while 95-octane gasoline contains 95% isooctane and 5% n-heptane. Occasionally using the wrong gasoline grade is not a problem—simply switch back to the correct grade after the tank is empty. However, long-term use of the wrong gasoline grade can have the following effects: Using a lower-octane gasoline in a high-compression engine can cause engine knocking. The lower octane rating reduces the gasoline's ignition point, causing it to ignite prematurely during the compression stroke. If combustion occurs before the spark plug fires, resistance will develop during the upward stroke. This resistance makes the engine run very unevenly. Mild knocking may only increase noise without significant engine damage, but noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, potentially leading to cylinder scuffing. Tips for Choosing Gasoline: Select gasoline with appropriate volatility based on the car's operating temperature. Highly volatile gasoline makes cold starts easier and ensures smooth engine warm-up, but excessive volatility can cause vapor lock in fuel lines, preventing the fuel pump from functioning properly and leading to engine stalling. Check whether your car is equipped with emission control devices like catalytic converters or oxygen sensors. If so, unleaded gasoline must be used to avoid damage and unnecessary repair costs. Important Notes: Choosing the correct gasoline grade is crucial. Most vehicles have the manufacturer's recommended gasoline grade printed inside the fuel filler cap—follow this guidance. If the label states "Use 92-octane or higher," you can use either 92-octane or 95-octane gasoline, but do not mix them. If the label states "Use no less than 95-octane," only 95-octane or 98-octane gasoline should be used—never 92-octane. A higher octane rating is not always better—the engine's compression ratio must match the gasoline grade. Using higher-octane gasoline in a low-compression engine may reduce knocking but can alter ignition timing, increasing carbon buildup in the cylinders and shortening engine lifespan over time. Using lower-octane gasoline in a high-compression engine can cause knocking, accelerating wear and tear on engine components.

[MacTravis]

As a car enthusiast, I can say that adding 98-octane gasoline to a car recommended for 95-octane is completely fine. 98-octane has a higher octane rating and better anti-knock properties, and most modern engines can adapt to mixed fuels without causing damage. However, when the engine is designed for 95-octane, using 98 is simply a waste of money unless the car's manual specifies the need for high-octane fuel in high-performance vehicles. Occasionally mixing in 98 when no other option is available at the gas station is also harmless, as the engine control unit can smoothly transition without causing malfunctions. That said, it's not cost-effective—98-octane is significantly more expensive than 95, and long-term use is a waste of money unless your car has modifications like an upgraded exhaust system for increased power, in which case the performance gains are minimal and hardly noticeable. The key is to refer to the owner's manual and stick to the recommended fuel grade to prevent potential carbon buildup risks, maintain engine longevity, and ensure safe usage—safety always comes first.