Can Different Grades of Gasoline Be Mixed?
3 Answers
Gasoline can be mixed, and here are the relevant details: Mixing gasoline is possible: For gasoline from different companies, the state has strictly standardized the main components of additives in gasoline. Even if mixed, it will not cause harm. In emergency situations, gasoline from Sinopec and PetroChina can be mixed occasionally, but from a long-term perspective, it is not recommended to mix gasoline from different oil companies. Gasoline composition: Gasoline mainly consists of C5-C12 aliphatic hydrocarbons and cycloalkanes, along with a certain amount of aromatic hydrocarbons. Gasoline has a high octane number (anti-knock combustion performance) and is classified into grades such as 89, 92, and 95 based on the octane number. Gasoline is produced by refining different gasoline components obtained from petroleum refining, including straight-run gasoline components, catalytic cracking gasoline components, and catalytic reforming gasoline components, which are then blended with high-octane components. It is primarily used as fuel for spark-ignition internal combustion engines in automobiles.
A while ago, I encountered a situation during a long drive where the gas station only had 95-octane fuel, while my tank still had half a tank of 92-octane left. After consulting a mechanic, I learned that occasionally mixing different octane ratings isn’t a big issue—especially mixing a lower octane with a higher one, which can even slightly improve anti-knock performance. The key is to check the car manufacturer’s manual for the minimum required octane rating. My older car requires 92-octane or higher, and mixing in 95-octane actually made it run smoother. However, avoid long-term mixed usage, as different octane fuels have varying additive formulations that can worsen combustion chamber carbon buildup. After an emergency mix, try to burn through that tank quickly and then stick to a single octane rating—this is gentler on fuel injectors and oxygen sensors. Next time you refuel, remember to check the octane label inside the fuel filler cap and follow the manufacturer’s standards for the safest approach.
Remember during my last road trip in the mountains, I mixed half a tank of 93 and 97 octane gasoline at a gas station. This occasional mixing won't directly damage the engine, but turbocharged cars should still try to avoid it. The main difference between octane ratings lies in the anti-knock properties - mixing effectively alters the fuel's detonation resistance. For high-compression ratio engines, mixing lower octane fuel may cause cold start difficulties or even knocking. Short-term mixing can be managed through the ECU's adaptive ignition timing adjustment, but long-term mixing may accelerate catalytic converter aging. It's recommended to refuel when the low fuel light comes on rather than waiting until nearly empty, as this reduces mixing chances.
