Should the Peugeot 408 use 92 or 95 octane gasoline?
2 Answers
According to the official vehicle manual recommendation, the Peugeot 408 should use 92 octane gasoline. In addition to checking the suitable gasoline grade in the vehicle manual, the Peugeot 408 can also check it on the fuel tank cap, which will also be marked. Usually, the 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 choose 92 octane gasoline, while those with a compression ratio between 10.0-11.5 should choose 95 octane gasoline. However, with the use of some new technologies, the gasoline grade cannot be determined solely by the compression ratio. A high compression ratio can also be tuned to use low-grade gasoline. This is because, in addition to 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 Peugeot 408 occasionally uses the wrong gasoline grade, simply switch back to the correct grade after use. However, long-term use of the wrong gasoline grade may have the following effects: For vehicles recommended to use low-grade gasoline, using high-grade gasoline by mistake will not cause damage, but the increase in octane number will change the fuel's ignition point, leading to delayed combustion in the engine. This means both the engine's power output and thermal efficiency will decrease, resulting in poorer performance. For vehicles recommended to use high-grade gasoline, using low-grade gasoline may cause engine knocking. Because the octane number is too low, the gasoline's ignition point decreases and may ignite prematurely during the compression stroke. If the fuel ignites before the spark plug fires during the compression stroke, resistance will occur during the upward stroke. This resistance will make the engine run very unstably. If it is mild knocking, it only increases noise and does not significantly damage the engine. However, if there is obvious knocking, it indicates severe engine conditions. The vibration not only affects driving stability but also causes abnormal wear on the pistons and cylinders, and in severe cases, may even lead to cylinder scoring.
I've been driving a Peugeot 408 for many years and usually fill it with 95-octane gasoline because the manual recommends it, stating that the engine is optimized with a high compression ratio to prevent knocking issues. I've tried 92-octane a few times and noticed increased engine noise, occasional stuttering during acceleration, likely due to incomplete combustion and more carbon buildup. In the long run, although 95-octane is more expensive, it offers better fuel efficiency, saving a bit of fuel per 100 kilometers and avoiding costly repairs. I also recommend regularly checking the fuel cap label to confirm the octane rating and not blindly saving money at the expense of the car. For daily driving, sticking to 95-octane ensures smoother and safer operation.
