Why is the refueling amount larger than the fuel tank capacity?

[LawsonFitz]

Car refueling amount is larger than the fuel tank capacity because there is a 5% difference between the rated capacity and the actual capacity of the fuel tank. For example, if the rated capacity is 95 liters, its actual capacity can reach at least 100 liters. It is understood that this error will be further amplified during the manufacturing process of the automobile factory. Most automobile manufacturers increase the "actual capacity" of the fuel tank by 7% or even 10% over the "rated capacity" to improve the safety factor of the car. The gasoline tank of a car is composed of components such as the filler pipe, filter, and filler extension pipe. In a full state, the actual refueling capacity consists of the gasoline in the tank, filler pipe, and filler extension pipe, while the fuel tank capacity marked on the car's factory manual specifically refers to the capacity of the tank itself, excluding the refueling capacity of the connecting pipeline between the tank and the filler port. Refueling precautions: It is wrong to refuel after the fuel tank alarm sounds. It is best not to wait for the fuel tank alarm to refuel. The car's fuel pump is located in the fuel tank. When the fuel tank alarm sounds, the fuel pump will be exposed in the fuel tank. Prolonged exposure in this state can damage the gasoline pump.

[DelJack]

I've been driving a taxi for 20 years, and it's quite common to fill beyond the tank's rated capacity. Last week when the fuel light came on, I refueled what was labeled as a 55-liter tank but ended up taking 58 liters. The gas station attendant explained that the labeled capacity is the safe volume, while the actual capacity is larger. It's like a thermos labeled 1.5 liters that can actually hold 1.8 liters of water. The upper part of the tank needs space for gasoline vapors; otherwise, summer heat could cause the gasoline to expand and damage the tank. Also, when the pump nozzle clicks off, you can usually add a bit more, though I don't recommend filling it to the brim—gasoline fumes can seep into the cabin. Experienced drivers know to leave some room to avoid leaks that could dirty the trunk.

[LaGemma]

It is an industry practice for a car's fuel tank to have an actual capacity about 10% larger than the labeled volume. When I previously disassembled a fuel tank for repair and measured it, I found that a tank labeled as 50 liters could actually hold up to 55 liters. This design reserve space primarily considers three factors: providing room for gasoline expansion due to heat to release pressure, preventing liquid fuel from entering the evaporation system when the vehicle is climbing, and accounting for the volume occupied by foam during refueling. Exceeding the labeled fuel volume is not a major concern, but consistently filling the tank to the brim can saturate the carbon canister. I've seen many drivers forcefully fill their tanks to the very top, resulting in a strong gasoline smell inside the car.

[LeilaAnn]

Have you ever noticed that after the fuel nozzle automatically stops, you can still manually top up a few more liters? It's quite normal for the actual capacity of the fuel tank to exceed the manual's stated figure by seven or eight liters. I used to work in assembly at an automobile factory, and tests showed that foam is generated when gasoline is injected—the nominal volume is calculated based on the liquid reaching full level. The curved structure from the fuel tank opening to the filler pipe also holds fuel, which isn't included in the calibrated volume. More importantly, there's a safety buffer—last summer, my colleague's car had gasoline overflow from the pressure relief valve after being parked in the sun at noon because it was filled too full, leaving a puddle in the parking lot.