BMW Mini: Should I Use 92 or 95 Octane Gasoline?

[LucilleLee]

According to the official vehicle manual recommendation, the BMW Mini should use 95 octane gasoline. In addition to checking the suitable gasoline grade in the vehicle manual, you can also find it on the fuel tank cap, which will also be indicated. Usually, the gasoline grade can also be determined based on the engine's compression ratio. Vehicles 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. However, with the application of some new technologies nowadays, the gasoline grade cannot be solely determined by the compression ratio. A high compression ratio can also be tuned to use lower-octane gasoline because, apart from 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 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane. If you occasionally use the wrong gasoline grade in your BMW Mini, simply switch back to the correct grade after consumption. However, long-term use of the wrong gasoline grade may have the following effects: For vehicles recommended to use lower-octane gasoline, using higher-octane gasoline will not cause damage, but the increase in octane number will alter the fuel's ignition point, leading to delayed combustion in the engine. This means both the engine's power output and thermal efficiency will decrease, resulting in poorer performance. For vehicles recommended to use higher-octane gasoline, using lower-octane gasoline may cause engine knocking. Because the octane number is too low, the gasoline's ignition point decreases and may ignite prematurely during the compression stroke. If combustion occurs before the spark plug ignites during the compression stroke, resistance will arise during the upward stroke. This resistance can make the engine run very unstably. If the knocking is mild, it may only increase noise without significant damage to the engine. However, if the knocking is severe, it indicates that the engine's condition is already very serious. The vibration not only affects driving stability but can also cause abnormal wear on the piston and cylinder, and in severe cases, even cylinder scoring.