What grade of gasoline should the Volkswagen CC use?

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The Volkswagen CC should use 95-octane gasoline, as this is the recommended grade specified in the vehicle's official user manual. In addition to checking the suitable gasoline grade in the user manual, you can also find it indicated on the fuel tank cap of the Volkswagen CC. Generally, the appropriate 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 application of some new technologies, the compression ratio alone cannot determine the gasoline grade, as high compression ratio engines can also be tuned to use lower octane gasoline. This is 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 octane rating, 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 Volkswagen CC 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 lower octane gasoline, using a higher octane grade will not cause damage, but the increase in octane number may alter the fuel's ignition point, leading to delayed combustion in the engine. This results in reduced engine power and thermal efficiency, with the practical effect being poorer performance. For vehicles recommended to use higher octane gasoline, using a lower octane grade can cause engine knocking. This is because the significantly lower octane number reduces the gasoline's ignition point, causing it to ignite prematurely during the compression stroke. If combustion occurs before the spark plug fires during the compression stroke, resistance will be encountered during the upward stroke. This resistance makes the engine run very unevenly. If the knocking is mild, it may only increase noise without obvious engine damage. However, noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on the pistons and cylinders, and in severe cases, cylinder scoring.