Should You Use 92 or 95 Octane Gasoline for Your Car?
2 Answers
The octane rating of gasoline for a car should generally follow the recommendations in the vehicle's official owner's manual. In addition to checking the appropriate octane rating in the owner's manual, you can also find this information on the fuel tank cap, which typically indicates the recommended rating. The octane rating 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, while those with a compression ratio between 10.0-11.5 should use 95 octane gasoline. For higher compression ratios, 98 octane gasoline is recommended. However, with the use of new technologies, the compression ratio alone may not be the sole determinant of the appropriate octane rating. High compression ratio engines can sometimes be tuned to use lower octane gasoline. Other factors, such as ignition timing, turbocharging technology, and Atkinson cycle technology, also play a role. Generally, the higher the 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. Occasionally using the wrong octane rating is not a problem—simply switch back to the correct rating after the tank is empty. However, prolonged use of the wrong octane rating can have the following effects: For vehicles designed for lower octane gasoline, using a higher octane rating will not cause damage. However, 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. For vehicles designed for higher octane gasoline, using a lower octane rating can cause engine knocking. Because the octane number is significantly lower, the fuel's ignition point decreases, causing premature ignition during the compression stroke. If the fuel ignites before the spark plug fires, it creates resistance during the upward stroke. This resistance makes the engine run very unevenly. Mild knocking may only increase noise without noticeable engine damage, but severe knocking indicates serious engine issues. The vibrations not only affect driving stability but can also cause abnormal wear on the pistons and cylinders, potentially leading to severe damage like cylinder scoring.
I've been driving a regular family car for seven or eight years, and I usually opt for 92-octane gasoline as my first choice because it's cheaper and suitable for most economy cars. Of course, not all cars are like this. I once drove a friend's car, and his manual specified 95-octane fuel because it had a turbocharged engine, which is prone to knocking. Knocking refers to abnormal engine vibrations with a crackling sound, and using lower-octane fuel might damage the cylinders. I always check the label on the fuel tank cap—for example, my compact car says 'RON 92,' representing an octane rating of 92, equivalent to the domestic 92-octane. If the manual doesn't specify, I recommend trying 92-octane first; it's generally fine for city driving, but switching to 95-octane is safer when frequently climbing mountains. Never overlook this to save a little money—using the wrong fuel grade long-term can increase maintenance costs. During every service, the technician also reminds me not to mix fuel grades randomly.
