Why can a 40-liter fuel tank hold 45 liters of fuel?
2 Answers
The reason a 40-liter fuel tank can hold 45 liters of fuel is that gasoline is volatile and expansive. Car fuel tanks are designed to be about 5%-10% larger than their standard capacity, so the fuel dispenser may show a higher volume than the tank's nominal requirement. According to the national mandatory standard "Safety Performance Requirements and Test Methods for Automotive Fuel Tanks," the nominal capacity of a car fuel tank should be controlled at 95% of its maximum liquid capacity. Some car brands reserve a 10% capacity space, so the labeled capacity of the fuel tank is smaller than its actual capacity. In fact, during the manufacturing process, the difference between the actual volume and the rated volume can be further amplified. All objects expand when heated and contract when cooled, so the standard volume of a car fuel tank is not equal to its actual volume. Normally, the fuel tank capacity shown in the vehicle's parameter table or labeled on the fuel cap only represents the maximum reasonable capacity. Car fuel tanks have both a rated volume and an actual volume, which differ. The state does not classify automotive fuel tanks as measuring instruments but only as containers, which lack measurability. Therefore, they cannot be used as a basis for judging measurement accuracy, and the rated capacity of the fuel tank cannot be used as the fundamental criterion for determining the accuracy of the refueling volume.
I think it's quite common for a fuel tank with a nominal capacity of 40 liters to actually hold 45 liters. The main reason is that car manufacturers design fuel tanks with a safety margin to account for thermal expansion and contraction. When gasoline is at a lower temperature, it has a higher density and smaller volume, allowing more fuel to be filled without risking overflow or leakage. I've driven several cars myself, and every time I refuel in cold weather or when the gas station's fuel temperature is low, a nominally 40-liter tank can easily take 42 or 43 liters, and occasionally even 45 liters. As long as there's no smell of gasoline, it's fine. This isn't a big issue—it's more about safety considerations, so don't worry about the fuel pump or fuel gauge being faulty.
