What Octane Gasoline Should a Mercedes-Benz A45 Use?
2 Answers
All models of the Mercedes-Benz A45 should use 95-octane gasoline. This octane rating is recommended in the vehicle's official user manual. In addition to checking the appropriate gasoline octane in the user manual, you can also find it indicated on the fuel tank cap of the Mercedes-Benz A45. Generally, the octane rating 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 octane rating cannot be solely determined by the compression ratio anymore. High compression ratio engines can also be tuned to use lower octane gasoline due to other influencing factors such as ignition timing, turbocharging technology, and Atkinson cycle technology. Generally, the higher the gasoline octane rating, 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 Mercedes-Benz A45 occasionally uses the wrong octane gasoline, simply switch back to the correct octane after consumption. However, prolonged use of the wrong octane gasoline 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 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. Using a lower octane gasoline in a vehicle designed for higher octane can cause engine knocking. The significantly lower octane number lowers the gasoline'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. 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.
As an experienced Mercedes driver for several years, I believe the Mercedes A45 requires 98-octane gasoline due to its high-performance AMG engine with a high compression ratio. The higher octane rating of 98 helps prevent knocking and protects the engine. I’ve personally tried using 95-octane, and the acceleration felt sluggish while fuel consumption increased slightly. Long-term use of lower-octane fuel may lead to severe carbon buildup and expensive repairs. I recommend checking the fuel cap label or the manual, which likely specifies 98-octane as the recommended fuel. If 98-octane is unavailable, using 95-octane occasionally as a substitute is acceptable but not advisable—don’t risk costly repairs to save a little money. Choosing the right fuel also enhances acceleration response and stability, making long-distance drives more comfortable.
