What grade of gasoline should a BMW X5 use?

[MacElias]

BMW X5 should use 95-octane gasoline, as recommended in the vehicle's official user manual. In addition to checking the appropriate gasoline grade in the user manual, BMW X5 owners can also find this information on the fuel tank cap, which will be clearly marked. Generally, 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. If the compression ratio is higher, 98-octane gasoline is recommended. However, with the use of new technologies, the gasoline grade cannot be solely determined by the compression ratio, as high-compression engines can also be tuned to use lower-octane gasoline. This is because 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 rating 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 a BMW X5 occasionally uses the wrong gasoline grade, simply switching back to the correct grade after use is sufficient. However, long-term use of the wrong gasoline grade can have the following effects: For vehicles recommended to use low-octane gasoline, using a higher-octane grade will not cause damage, but the increased octane rating can alter the fuel's ignition point, leading to delayed combustion in the engine. This reduces both the engine's power output and thermal efficiency, resulting in poorer performance. For vehicles recommended to use high-octane gasoline, using a lower-octane grade can cause engine knocking. The significantly lower octane rating 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. This resistance makes the engine run very unstably. Mild knocking only increases noise without obvious engine damage, but severe knocking indicates serious engine conditions. The vibrations not only affect driving stability but also cause abnormal wear on pistons and cylinders, potentially leading to cylinder scoring in severe cases.