What are the precautions for changing gasoline grades?

[DiLena]

The main precautions for changing gasoline grades are as follows: The viscosity of the engine oil should be as low as possible: Under the premise of ensuring reliable lubrication of the engine, the viscosity of the engine oil should be as low as possible. High-viscosity engine oil is only suitable for severely worn engines or for use in the southern summer. Blindly choosing high-viscosity engine oil will increase the resistance during engine operation, thereby increasing fuel consumption. Multi-grade oil should be used whenever possible: Multi-grade oil has excellent viscosity-temperature performance, lasts longer in engines, saves fuel, is suitable for all seasons, and is easier to manage. When using multi-grade oil, the oil color tends to darken, and the oil pressure is slightly lower than that of conventional oil. These are normal phenomena and do not affect usage.

[LeKaleb]

Last time my friend switched his Civic from 95-octane to 92-octane fuel without clearing the tank first, and problems arose—the engine felt sluggish when accelerating. Changing fuel grades isn't something to do casually—the recommended octane rating in the car's manual is the best reference. Turbocharged cars are especially prone to knocking if forced to use lower-octane fuel. For older cars switching to higher-octane fuel, it's advisable to keep half a tank of the old fuel and add the new fuel gradually for transition. A sudden full switch might loosen carbon deposits and clog the fuel injectors. If you notice weak acceleration and shaking over two or three full tanks of fuel, take the car to the shop immediately to check the oxygen sensor—don’t tough it out like my friend, who ended up spending over 2,000 RMB on repairs after two months. The same transitional approach should be taken when switching gas station brands, as mixing different fuel additives can really upset the engine.

[DelValerie]

After running an auto repair shop for ten years, I've found three common pitfalls when switching gasoline grades: turbocharged cars mistakenly filled with lower octane, mixing different brands of fuel, and frequent grade changes without cleaning the fuel system. Transitioning from 92 to 95 octane can be done gradually, but switching from 95 to 92 requires completely draining and cleaning the fuel tank first—otherwise, engine knocking could damage piston rings. Mixing different gasoline brands is like blending Coke with Sprite; it's fine for short-term emergencies but will definitely cause sediment buildup long-term. Ideally, use up most of the tank before switching brands. The most overlooked aspect is fuel injector cleaning—for vehicles that frequently change octane grades, use specialized cleaner every six months, or you might mistake injector issues for spark plug problems someday. Remember: the recommended octane rating on your fuel cap is always more reliable than gas station attendants' suggestions.

[StJoseph]

Changing oil grades sounds simple, but there are hidden complexities. Using lower-grade oil in turbocharged vehicles doesn't just increase fuel consumption – severe cylinder knocking (audible as a rattling sound) essentially means the engine is self-destructing. Naturally aspirated engines need a transition period when switching from 92 to 95 octane: ideally mix fuels for the first three refills (gradually decreasing the old grade from 2/3 to 1/3) to let the ECU gradually adapt to the new air-fuel ratio. However, when downgrading grades, you must completely drain the tank at a reputable gas station before refilling – impurities clogging the high-pressure fuel pump would cost you two years' worth of premium fuel in repairs. Older vehicles demand special caution: decades-old varnish deposits in the tank reacting with new additive formulations can create blockages worse than mentos in coke, leaving you stranded in frustration.