Precautions for Switching from 98 Octane to 95 Octane Gasoline?
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When switching from 98 octane to 95 octane gasoline, it's important to note that occasional changes won't have an impact. However, long-term use of gasoline with different octane ratings can lead to delayed ignition in the car's engine, resulting in reduced engine power and thermal efficiency. The practical feedback is a noticeable decrease in performance, which can advance the vehicle's major overhaul timeline. The appropriate gasoline grade can be determined based on the engine's compression ratio. Cars with an engine compression ratio between 10.0 and 11.5 should opt for 95 octane gasoline, while those with higher compression ratios should choose 98 octane. However, with the advent of new technologies, the compression ratio alone isn't the sole determinant of the suitable gasoline grade. High compression ratio engines can also be tuned to use lower octane gasoline, as factors like ignition timing, turbocharging technology, and Atkinson cycle technology also play a role. Generally, higher octane gasoline has a higher octane number and better anti-knock properties. 98 octane gasoline contains 98% isooctane and 2% n-heptane, whereas 95 octane gasoline consists of 95% isooctane and 5% n-heptane. Occasionally using the wrong gasoline grade only requires switching back to the correct one after consumption. However, prolonged use of the incorrect octane rating can have the following effects: Using lower octane gasoline in a vehicle designed for higher octane can cause engine knocking. This occurs because the significantly lower octane rating reduces the gasoline's ignition point, causing premature ignition during the compression stroke. If the fuel ignites before the spark plug fires, resistance is created during the upward stroke. This resistance leads to unstable engine operation. Mild knocking may only increase noise without obvious engine damage, but noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, potentially leading to cylinder scoring. Additional considerations when selecting gasoline include: Choosing gasoline with appropriate volatility based on the vehicle's operating environment temperature. Gasoline with good volatility facilitates cold starts and ensures balanced engine warm-up. However, excessively high volatility can easily cause vapor lock in the fuel lines, preventing the fuel pump from functioning properly and leading to engine stalling. Selecting gasoline based on lead content. It's essential to know whether your car is equipped with emission control devices, such as a catalytic converter or oxygen sensors. If these devices are present, unleaded gasoline must be used to avoid damage from lead, which could result in unnecessary additional repair costs.
I usually drive an old Camry and have switched between different fuel grades several times. Switching from 98 to 95 is completely fine, but it depends on the engine type. Naturally aspirated engines generally don’t require much attention, but turbocharged or high-compression engines need to watch out for knocking. Before refueling, drive until the tank is down to 1/4, and when mixing fuels, remember to add a bottle of fuel additive. Last time after switching, I noticed the throttle felt lighter on the highway, though the cold-start sound was a bit muffled. Sinopec’s 95-octane fuel has good cleanliness, and after two tanks, the fuel consumption stabilized at 8.2 L/100km, saving over 200 yuan per month compared to 98-octane. Be careful not to go to small gas stations—95-octane mixed with 92 can damage the fuel injectors.
