Should the LaCrosse 2.4 use 92 or 95 octane gasoline?

[EllaAnn]

According to the official vehicle manual recommendation, the LaCrosse 2.4 should use 95 octane gasoline. In addition to checking the appropriate gasoline grade in the vehicle manual for the LaCrosse 2.4, you can also find it on the fuel tank cap, which will be clearly marked. Typically, 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, those between 10.0-11.5 should use 95 octane gasoline, and if the compression ratio is higher, 98 octane gasoline should be selected. However, with the application of some new technologies, the gasoline grade cannot be solely determined by the compression ratio. High compression ratio engines 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 the LaCrosse 2.4 occasionally uses the wrong gasoline grade, simply switch back to the correct grade after consumption. However, long-term use of the wrong gasoline grade can 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 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, resulting in poorer performance in actual driving experience. For vehicles recommended to use higher octane gasoline, using lower octane gasoline can cause engine knocking. Because the octane number is too low, the gasoline's ignition point decreases and it may ignite prematurely during the compression stroke. If combustion occurs before the spark plug fires during the compression stroke, resistance will arise during the upward stroke. This resistance will make the engine run very unstably. If the knocking is imperceptible, it only increases noise without significant damage to the engine. However, if noticeable knocking occurs, it indicates severe engine conditions. The vibration not only affects driving stability but also causes abnormal wear on the piston and cylinder, and in severe cases, can lead to cylinder scoring.