What grade of gasoline should the Jetta VS5 use?

[CassidyMarie]

Jetta VS5 should use 95-octane gasoline, as this grade is recommended in the vehicle's official user manual. In addition to checking the appropriate gasoline grade in the user manual, the Jetta VS5's fuel cap also indicates the recommended grade. 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 application of new technologies, the compression ratio alone cannot determine the gasoline grade, as high compression ratios can be adjusted to use lower-octane gasoline. 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 Jetta VS5 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 for lower grades, using a higher grade will not cause damage, but the increase in octane number can alter the fuel's ignition point, leading to delayed combustion in the engine. This reduces the engine's power output and thermal efficiency, resulting in poorer performance. For vehicles recommended for higher grades, using a lower grade can cause engine knocking. The significantly lower octane number 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, making the engine run very unstable. Mild knocking only increases noise without significant engine damage, but severe knocking indicates serious engine conditions, affecting driving stability and causing abnormal wear on pistons and cylinders, potentially leading to cylinder scoring.