Should the G-Class use 95 or 98 octane fuel?
2 Answers
According to the official vehicle manual recommendation, the G-Class should use 95 octane gasoline. In addition to checking the appropriate gasoline grade in the vehicle manual, the G-Class owner can also find this information on the fuel tank cap, which is usually labeled. Typically, the 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, while those with a compression ratio between 10.0-11.5 should use 95 octane gasoline. However, with the application of new technologies, the compression ratio alone cannot determine the appropriate gasoline grade. High compression ratio engines can still be tuned to use lower octane fuel because factors other than compression ratio also play a role, such as ignition timing, turbocharging technology, and Atkinson cycle technology. 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 G-Class 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 fuel, using higher octane gasoline will not cause damage, but the increase in octane value will alter the fuel's ignition point, leading to delayed combustion in the engine. This means the engine's power output and thermal efficiency will decrease, resulting in poorer performance. For vehicles recommended to use higher octane fuel, using lower octane gasoline can cause engine knocking. Because the octane value is significantly lower, the reduced ignition point may cause premature ignition 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 makes the engine run very unstable. If the knocking is imperceptible, it only increases noise without obvious engine damage. However, noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, and in severe cases, cylinder scoring.
I've driven a G-Class for several years and found that 98-octane gasoline works best. The manual recommends 98-octane, as the engine has a higher compression ratio, and higher-octane fuel reduces the risk of knocking. When refueling, choosing 98-octane makes the engine more responsive, accelerates faster, and provides better stability on highways. While 95-octane is also usable—the manual states it as the minimum requirement—spending a bit more on 98-octane is more worry-free and lowers long-term maintenance costs. I’ve also tried mixing fuels, which I don’t recommend, as inconsistent fuel quality can lead to carbon buildup. Remember, the gas station brand matters too—stick to major suppliers like Sinopec to ensure fuel purity. In short, follow the manufacturer’s advice and don’t skimp on quality.
