Jetta VS5: Should I Use 92 or 95 Octane Gasoline?

[MacSilas]

According to the official vehicle manual recommendation, the Jetta VS5 should use 95 octane gasoline. In addition to checking the appropriate gasoline grade in the vehicle manual, you can also find it on the fuel tank cap, which will also be 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. However, with the application of some new technologies, the gasoline grade cannot be solely determined by the compression ratio. A high compression ratio 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 octane number, the higher the octane value 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 you occasionally use the wrong gasoline grade in the Jetta VS5, 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 value 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 value is much lower, the gasoline's ignition point decreases and 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 it's only mild knocking, it may just increase noise without significant damage to the engine. However, if there is noticeable knocking, it indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, and in severe cases, cylinder scoring.