According to the official vehicle manual recommendation, the BMW X5 should use 95-octane gasoline, so there is no problem with using it. 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 marked. Usually, the gasoline grade can also be determined based on the engine's compression ratio. Cars 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 use of some new technologies nowadays, the gasoline grade cannot be determined solely by the compression ratio. A high compression ratio can also be adjusted to use lower-octane gasoline because, besides 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 the BMW X5 occasionally uses the wrong gasoline grade, simply switch back to the correct grade after using it up. However, long-term use of the wrong gasoline grade can have the following effects: For vehicles recommended for lower grades, using higher-octane gasoline will not cause damage, but the increase in octane number will change 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, with the actual feedback being poorer performance. For vehicles recommended for higher grades, using lower-octane gasoline can cause engine knocking. Because the octane number is too low, the gasoline's ignition point decreases, causing it to ignite prematurely during the compression stroke. If the fuel ignites before the spark plug fires during the compression stroke, resistance will occur during the upward stroke. This resistance makes the engine run very unstable. If the knocking is imperceptible, it only increases noise and does not significantly damage the engine. However, if the knocking is noticeable, it indicates severe engine conditions. The vibration not only affects driving stability but also causes abnormal wear on the pistons and cylinders, and in severe cases, can lead to cylinder scoring.
