The Invisible Cost of the Thermometer: How Ambient Temperature Affects Fuel Consumption in Transport

In a sector as sensitive to margins as road transport, every cent counts. In Spain, where thermometers fluctuate between scorching summer heatwaves and freezing winter days, there is a silent factor that directly impacts profitability: ambient temperature and its effect on fuel density.
Far from being anecdotal, this physical phenomenon translates into less efficient purchase volumes and, ultimately, higher operating costs for fleets. Understanding it is the first step toward smarter refueling.
The key lies in a basic property of liquids: density, which varies with temperature. Diesel and gasoline, like most fluids, expand with heat and contract with cold. This means that a liter of fuel on an extremely hot day (at 35°C, for example) contains less energy mass—fewer molecules capable of producing work—than that same liter measured on a freezing morning (at 5°C).
The gas station pump measures volume (liters), not mass (kilograms) or energy. Therefore, when refueling in hot weather, even if the tank is filled, you are acquiring, in real terms of power, less fuel for the same price.
Faced with this physical reality, transporters can adopt simple yet effective logistical strategies. The main recommendation is to schedule refueling for large trucks during the coolest parts of the day: preferably early in the morning or at night. During these hours, the temperature of the fuel stored in the underground tanks at service stations is lower, as it is more protected from ambient heat.
Thus, for the same money and the same volume, you obtain a denser and more energy-rich fuel, which translates into extra kilometers of range per tank.
This practice should be complemented with other efficiency measures. Keeping tanks as full as possible reduces internal space for evaporation and air formation, and planning routes to minimize idling time and excessive use of cabin air conditioning or heating are equally crucial habits.
It’s not just about when to refuel, but how to optimize what is refueled. In a context of high volatility in fuel prices, these decisions make the difference in a company’s bottom line.
Ultimately, Spain’s climate challenge adds a layer of complexity to transport management. Beyond tire pressure or efficient driving, the seasoned transporter knows they must “hunt” for the lowest temperatures to fill their tanks. It is a game of physics applied to the domestic economy of the road, where gaining a few grams of density per liter can mean, at the end of the year, tangible savings in a business where competition is fierce and costs are relentless.