Should the Audi A5 use 95 or 98 octane gasoline?
2 Answers
Audi A5 should use 95 octane gasoline, as this fuel grade is recommended 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 Audi A5. Typically, the appropriate fuel 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, those between 10.0-11.5 should use 95 octane gasoline, and 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 required 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 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 Audi A5 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 to use lower octane gasoline, using higher octane gasoline 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 to use higher octane gasoline, using lower octane gasoline can cause engine knocking. Due to the significantly lower octane number, the gasoline's ignition point decreases, causing premature ignition during the compression stroke. If detonation occurs before the spark plug ignites, resistance will arise during the upward stroke. This resistance makes the engine run very unstably. If the knocking is imperceptible, it only increases noise without obvious damage to the engine. 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.
This issue deserves thorough discussion. For Audi A5 owners, filling up with 95-octane gasoline as indicated on the fuel tank cap is perfectly adequate - the manual clearly states 95 as the minimum requirement. While 98-octane fuel has better anti-knock properties, such high octane levels are unnecessary for daily urban commuting. Consider this: 98-octane costs nearly 1 yuan more per liter than 95, meaning over 40 yuan extra per full tank - savings that could cover a maintenance service over time. I've seen people insist on using 98-octane only to find no improvement in fuel efficiency or power after six months. Of course, if you live in mountainous areas with frequent steep climbs or drive long distances in summer heat, using 98-octane for engine protection makes sense. The crucial point is never compromise with 92-octane to save money - that significantly increases the risk of triggering the engine warning light.
