What are the hazards of filling a car designed for 92-octane gasoline with 98-octane?
2 Answers
Switching from 92-octane to 98-octane gasoline will not cause damage, but it may lead to delayed combustion in the engine, with the actual feedback being reduced power performance. Occasionally using the wrong gasoline grade only requires switching 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 designed for lower octane grades, accidentally using higher octane gasoline will not cause damage, but the increase in octane rating will alter 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, with the actual feedback being reduced power performance. For vehicles designed for higher octane grades, using lower octane gasoline can cause engine knocking. Because the octane rating is too low, 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 significant 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. Besides checking the appropriate gasoline grade in the car's manual, it is also indicated on the fuel cap. Typically, the gasoline grade can also be determined based on the engine's compression ratio. Cars with a compression ratio between 8.6-9.9 should use 92-octane gasoline, those between 10.0-11.5 should use 95-octane, and higher compression ratios require 98-octane. However, with the use of new technologies, the compression ratio alone cannot determine the gasoline grade. 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 grade, the higher the octane rating 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.
I've been driving this car since I was twenty, and I often see people mistakenly thinking that using 98-octane gasoline can improve the performance of a car designed for 92-octane fuel. In reality, it can be harmful. I once tried using 98-octane fuel, and the engine sounded sluggish, while fuel consumption inexplicably increased by at least 10%. After a mechanic's inspection, it was found that incomplete combustion occurred, leading to rapid carbon buildup—within weeks, the spark plugs were covered in grime. If you keep doing this long-term, the repair costs won't be small; I spent 800 yuan last time just to clean the carbon deposits. The key issue is that 98-octane fuel is significantly more expensive than 92-octane, making it a complete waste of money. New drivers, don’t follow my mistake—stick to the 92-octane fuel recommended in your car’s manual; it’s the safest and most reliable choice. Regularly checking the spark plugs during maintenance can also help avoid major issues.
