Why Does the Fuel Amount Exceed the Tank Capacity?

[McRowan]

Most automobile manufacturers increase the actual fuel tank capacity by 7% or even 10% beyond the rated capacity to enhance vehicle safety. Additional details are as follows: Hazards of overfilling: Filling the tank to the brim increases the curb weight, leading to higher fuel consumption. It can easily block the air intake, causing the carbon canister to fail. Especially during high summer temperatures, excessive fuel can lead to gas expansion, resulting in fuel vapor overflow, which poses a fire hazard. If fuel flows into the air intake, it can affect the spark plugs, making the car unable to start. Main symptoms include: stalling during acceleration or even complete failure to start. Therefore, manufacturers take these factors into account when designing fuel tank capacity, leaving a certain amount of space in the car's fuel tank.

[MacKai]

I just noticed this issue because I've encountered it before. When the fuel filled exceeds the tank's labeled capacity, I believe it mainly relates to the tank design. Manufacturers usually indicate the basic storage space of the tank, but in reality, there's a safety margin during refueling to account for thermal expansion or pressure changes. The pipe space from the tank bottom to the nozzle is sometimes overlooked, allowing fuel to fill those gaps. The automatic stop mechanism on fuel nozzles isn't that precise, especially with high-speed nozzles, which might squeeze out a few extra liters. Temperature also plays a key role—in cold weather, fuel contracts less, allowing more to be added; the opposite happens in hot weather. In short, don't worry if you've added a bit extra, as long as it doesn't overflow and affect safety. I recommend paying attention to the fuel level during refueling and avoiding overfilling to the brim to prevent waste or damage to the carbon canister.

[DiBrandon]

As an enthusiast who frequently tinkers with cars, I've noticed that fuel tanks can hold more than their nominal capacity, primarily due to safety redundancies built into the manufacturing process. The geometric design of the tank, with its angled corners or bottom space, allows for extra fuel storage during refueling. Temperature effects: cold fuel has higher density and smaller volume, enabling more to be filled; hot fuel expands, reducing actual capacity. The pump nozzle's sensor doesn't stop immediately, often allowing an extra liter or two. Additionally, air trapped in the fuel tank lines gets compressed during refueling, freeing up space. This design ensures no fuel spillage during extreme driving conditions. However, overfilling isn't advisable—I've experienced it causing excessive pressure in the fuel system. That's why I always recommend refueling within reasonable limits to protect engine components.

[OKarter]

When I was learning to drive, I also wondered: why does my small car have a fuel tank labeled 50 liters, but the gas station can fill it up to 52 liters? Later, an experienced driver enlightened me by saying it's designed with extra space reserved. The fuel tank isn't completely filled like a bottle; a little space is left at the top to prevent expansion and cracking due to heat. The automatic stop of the fuel nozzle might be delayed, mistakenly allowing extra fuel to flow in. In winter, fuel contracts and takes up less space, so more can be filled. In summer, don't expect any extra. This issue made me realize the wisdom in car design. After learning this, I was no longer misled and only refueled as needed without being greedy. Paying a little more attention can avoid spills and trouble.