Is There a Difference Between Refueling in the Morning/Evening and at Noon?
3 Answers
There is no difference between refueling in the morning/evening and at noon. Fuel does expand with heat and contract with cold, but this occurs under natural conditions, and the entire fuel storage system at gas stations is equipped with a constant temperature control system. Therefore, the issue of fuel density being lower and the quantity being less due to thermal expansion at higher temperatures does not exist. Below are some precautions for refueling: Precautions: 1. Hearing a "whoosh" sound: When loosening the fuel tank cap, if you hear a "whoosh" sound, do not continue to open the fuel tank cap. Wait until the sound disappears before slowly opening it. In hot weather, high-pressure fuel may spray out from the fuel tank opening due to excessive internal pressure, causing personal injury. 2. Pay attention to the amount of fuel added: Do not overfill the fuel tank; stop at the first click of the fuel gun. Otherwise, fuel can easily enter the carbon canister, thereby reducing its service life.
I've been driving for over a decade and often hear friends discussing whether refueling in the morning or evening allows you to get more fuel. After actually keeping records, I found that in the morning when temperatures are lower, fuel density is slightly higher, so the same volume weighs a bit more. But in the city, daily temperature variations are small, typically differing by just a few tenths of a liter. For a 60-liter refill, you'd get less than half a liter extra. Annually, this might save you a few dozen yuan in fuel costs—hardly worth making a special effort to get up early or come home late. Honestly, there's no need to obsess over refueling times. I pay more attention to driving details: maintaining proper tire pressure, avoiding sudden braking, and not overusing the air conditioning. These small habits add up to greater fuel savings and are much easier to implement. Daily temperature fluctuations have minimal impact, so it's better to focus on safe driving.
Based on the principle of thermal expansion and contraction, fuel density is slightly higher during cooler morning/evening hours when temperatures are lower, meaning the same volume could potentially contain more energy. However, in reality, underground storage tanks at gas stations maintain stable temperatures with minimal daily fluctuations. With an average temperature difference of 5°C, the density variation is only about 0.7% – equating to just 0.4 liters more in a 60-liter fill-up. This translates to negligible annual fuel savings that won't impact your wallet. Don't treat this as some major secret; my data analysis shows urban temperature variations are too minor to matter. Other factors like fuel quality and air humidity actually have greater influence, making it unnecessary to adjust your refueling schedule.
