What does it mean to add small oil to a car?

[SanJessica]

Small oil mostly comes from underground refineries, or is a mixture of oil from regular channels and inferior oil, and its quality cannot be guaranteed. The following is the relevant introduction: 1. Gasoline: Gasoline is a volatile and flammable liquid hydrocarbon mixture distilled and cracked from petroleum, which can be used as fuel. It appears as a transparent liquid, is flammable, and has a distillation range of 30°C to 220°C. 2. Principle of thermal expansion and contraction: Thermal expansion and contraction refer to the property of objects expanding when heated and contracting when cooled. Since the movement of particles (atoms) inside an object changes with temperature, when the temperature rises, the vibration amplitude of the particles increases, causing the object to expand; but when the temperature drops, the vibration amplitude of the particles decreases, causing the object to contract.

[LeIsabella]

I've been driving for almost twenty years, and using small gas stations is nothing new to me. It's just about filling up at those privately-owned small gas stations to save some money. Two years ago, I often refueled at these places in the suburbs, and it turned out to be 1.2 yuan cheaper per liter compared to Sinopec. The first two months felt fine, but then the engine started sounding muffled, and the car would jerk like it was hiccuping when accelerating. After sending it for repairs, I found out that the fuel had too many impurities, clogging half of the fuel injectors. The cleaning and repair cost me over 800 yuan. If I had known, I really shouldn't have saved that little bit of money. Now I only refuel at official gas stations. Although it's more expensive, it gives me peace of mind. Cars are quite delicate; using the wrong fuel damages the internal parts, and repairs end up costing even more.

[VanArcher]

Using small gas stations means refueling at cheaper stations, especially those privately owned. I did the math: saving thirty bucks per full tank adds up to over two hundred a month. But later, my car started acting up—hard cold starts and creeping fuel consumption. The mechanic said small stations often have unstable fuel quality, lower octane ratings, and impurities. Cleaning the fuel system cost over six hundred, wiping out all the savings. Now I’ve wised up: sticking to reputable big brands ensures stricter fuel quality checks. In the long run, saving on repairs outweighs saving on fuel.

[DelRiver]

Adding 'small oil' refers to refueling through unofficial channels. Many roadside private gas stations sell this type of fuel at attractively low prices. However, the issue lies in the complex sources of these fuels—some are impurely refined, while others are mixed with unknown additives. Prolonged use can easily lead to carbon buildup in the engine, and clogged fuel lines are common. I've seen many cars that, after long-term use of such fuel, end up needing to replace fuel injectors or even repair cylinders. Repairs can cost anywhere from seven or eight hundred to several thousand yuan. So, when refueling, don't just chase cheap prices; checking the gas station's qualifications is safer. A stable car condition is more important than anything else.

[SanBriella]

It means going to small gas stations just to save money. I heard from relatives that these stations are cheaper, so I tried a few times. But after refueling, the car's acceleration noticeably slowed down, and the throttle felt sluggish. Later during maintenance at the 4S shop, the technician showed me with an endoscope—the cylinders were covered in a layer of black carbon deposits. They said it was caused by incomplete combustion of low-quality fuel. The cleaning cost over 500 yuan and delayed my car use for two days. Actually, if you do the math, the small savings per liter from cheap fuel are completely offset by just one engine cleaning. Since then, I've never set foot in small gas stations again.