What grade of fuel is suitable for the Passat?
2 Answers
The Passat should use 95-octane gasoline, as this fuel grade is recommended in the vehicle's official user manual. In addition to checking the appropriate fuel grade in the user manual, you can also find it on the fuel tank cap, which will be clearly marked. Typically, the fuel grade can also be determined based on the engine's compression ratio. Vehicles with a 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 use of some new technologies, the fuel grade cannot be determined solely based on the compression ratio. A high compression ratio can also be adjusted to use lower-octane gasoline, as 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 Passat occasionally uses the wrong gasoline grade, simply switch back to the correct grade after the current tank is used up. 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 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 reduces the engine's power output and thermal efficiency, resulting in poorer performance. For vehicles recommended to use higher-octane gasoline, using a lower grade can cause engine knocking. Since the octane number is significantly lower, the reduced ignition point may cause premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance will arise during the upward stroke, making the engine run very unstable. Mild knocking may only increase noise without obvious engine damage, but severe knocking indicates serious engine conditions. The vibrations not only affect driving stability but can also cause abnormal wear on the piston and cylinder, potentially leading to cylinder scoring in severe cases.
Passat owners should remember that filling up with 95 octane fuel is the most reliable. I've always adhered to this standard because Volkswagen engines are designed with a higher compression ratio. Using 92 octane fuel, although cheaper, can easily cause knocking and, over time, damage the pistons and spark plugs, leading to soaring repair costs. In fact, during the cold winter months, it's best to opt for 97 octane fuel to enhance cold-start performance, while 95 octane is sufficient in summer. Some friends try to save effort by using lower octane fuel, only to end up with weaker power and higher fuel consumption—a real case of being penny-wise and pound-foolish. Whether it's a new or old car, sticking to this habit is essential; don't be tempted by gas station discounts to make the wrong choice. During maintenance, always check the fuel cap sticker to confirm the requirements, as this can extend the engine's lifespan by at least three to five years.
