What Octane Gasoline Should a Passat Use?

[Preston]

The Passat should use 95-octane gasoline, as this fuel grade is recommended in the vehicle's official owner's manual. In addition to checking the suitable gasoline grade in the owner's manual, you can also find it indicated on the fuel filler cap. 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. For higher compression ratios, 98-octane gasoline is recommended. However, with the application of new technologies, the compression ratio alone cannot determine the required gasoline grade. 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 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 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: Using a higher-octane gasoline in a vehicle designed for lower octane will not cause damage, but the increased octane value 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. Using lower-octane gasoline in a vehicle designed for higher octane can cause engine knocking. Because the octane value is too low, the gasoline's ignition point decreases, causing it to ignite prematurely during the compression stroke. If combustion occurs before the spark plug fires, resistance is created during the upward stroke. This resistance makes the engine run very unstably. Mild knocking may only increase noise without significant engine damage, but noticeable knocking indicates severe engine conditions. The vibrations not only affect driving stability but can also cause abnormal wear on the pistons and cylinders, potentially leading to cylinder scoring in severe cases.