How much 92 left can be filled with 95?
3 Answers
You cannot fill 95 gasoline no matter how much 92 is left. If you occasionally fill up with the wrong gasoline grade, you just need to switch back to the correct gasoline grade after using it up. However, if you consistently use the wrong gasoline grade for a long time, it will have the following effects: For vehicles that recommend low-grade gasoline, filling up with high-grade gasoline will not cause damage, but the increase in octane number will change the ignition point of the fuel, leading to delayed ignition in the engine. This means both the engine's power output and thermal efficiency will decrease, and the actual feedback experience is reduced power; For vehicles that recommend high-grade gasoline, using low-grade gasoline will cause engine knocking. Because the octane number is too low, the ignition point of the gasoline decreases, causing it to ignite prematurely during the compression stroke. If the gasoline 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's mild knocking, it only increases noise and does not cause obvious damage to the engine. However, if there is noticeable knocking, it indicates that the engine's condition is already very severe. The vibration not only affects driving stability but also causes abnormal wear on the piston and cylinder, and in severe cases, can lead to cylinder scoring. In addition to checking the appropriate gasoline grade in the car's manual, you can also check it on the fuel tank cap, which will also indicate the recommended grade. Usually, the gasoline grade can also be determined based on the engine's compression ratio. Cars with an engine compression ratio between 8.6-9.9 should use 92 gasoline, while those with a compression ratio between 10.0-11.5 should use 95 gasoline. If the compression ratio is higher, 98 gasoline should be used. However, with the use of some new technologies nowadays, the gasoline grade cannot be solely determined by the compression ratio. Engines with high compression ratios can also be tuned to use low-grade 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 speaking, the higher the gasoline grade, the higher the octane number, and the better the anti-knock performance. 92 gasoline contains 92% isooctane and 8% n-heptane, while 95 gasoline contains 95% isooctane and 5% n-heptane.
I've been driving for over a decade and often get asked about mixing gasoline. The main difference between 92 and 95 is the anti-knock performance, and occasionally mixing them isn't a big issue. If there's only a quarter tank or less of 92 left (roughly when the fuel light comes on), adding 95 won't cause noticeable problems. In this case, the newly added 95 makes up the majority of the mixture, bringing the overall octane rating close to 95, and the engine will still run smoothly. However, don't make a habit of it—different gasoline grades have varying additive formulations, and long-term mixing might lead to slightly more carbon deposits. The most worry-free approach is to stick with the manufacturer's recommended fuel grade. If you must mix in an emergency, remember to add a bottle of fuel system cleaner to maintain the fuel lines.
Just heard the mechanics discussing this at the repair shop the other day. You can switch to 95 when there's about 10 liters of 92 left, roughly a quarter tank. The principle is simple - different octane ratings have varying knock resistance, but when the 92 residue drops below 25%, the newly added 95 quickly dilutes it, and the mixed fuel basically meets 95's octane standard. However, be reminded that turbocharged or direct injection engines are more fuel-sensitive, so it's better not to switch when below one-eighth tank. Also, never do the reverse - putting 92 in a 95-designed car may cause knocking and engine damage.
