Should the Old Reiz Use 92 or 95 Octane Gasoline?
2 Answers
According to the official vehicle manual recommendation, the old Reiz should use 92 octane gasoline. In addition to checking the appropriate gasoline grade in the vehicle manual, the old Reiz can also refer to the fuel cap, which usually indicates the recommended gasoline type. Typically, 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 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 gasoline grade, as high-compression engines can also 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 gasoline 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. If the old Reiz occasionally uses the wrong gasoline grade, simply switching back to the correct grade after consumption is sufficient. However, long-term use of the wrong gasoline grade may have the following effects: For vehicles recommended for lower octane gasoline, using higher octane gasoline will not cause damage, but the increased octane number may 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 recommended for higher octane gasoline, using lower octane gasoline may cause engine knocking. Due to the significantly lower octane number, the gasoline may ignite prematurely during the compression stroke before the spark plug fires, creating resistance during the upward stroke. This resistance makes the engine run very unstably. Mild knocking may only increase noise without significant engine damage, but severe knocking indicates serious engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, and in extreme cases, cylinder scoring.
My old Toyota Mark X has been running on 92 octane gasoline for nearly ten years. The manufacturer's manual clearly states that 92 octane is perfectly adequate, as the engine was designed with this fuel grade in mind. Although 95 octane is more expensive, it doesn't provide any noticeable power improvement in actual driving, only increasing operating costs. However, during summer when climbing hills with AC on, if I feel the engine struggling a bit, I occasionally fill up with 95 octane as a buffer. For older cars, just follow the recommended octane rating sticker behind the fuel filler cap - no need to waste money unnecessarily.