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Filling up in the morning: myth or reality?
I am often asked whether it is true that you can save money filling up early in the morning when the temperature is cooler. I always respond as such: this is an urban legend. And I am not alone: see what the people from Consumer Reports think.
In theory as well as in practice, a liquid contracts at low temperatures and expands when the temperature rises. It would therefore be an advantage to fill up with cold gasoline at an equivalent volume, since as measured at the pump, it contains more energy. An anecdote: some racing teams (in Formula 1) had the habit of chilling their reserve to get more into the car during refuelling. The equipment would have to be arranged to avoid seeing the unsightly refrigerated trucks in the stands. Not only that, it would be dangerous. Maybe the myth of filling up in the morning comes from this practice? Do you have any idea where it comes from?
Whether or not this is true, in practice it means very little. Because gasoline is stored in underground tanks where the temperature is relatively constant whatever the time of day or night. Obviously, in warm weather the gasoline in the pump may have a higher temperature (and would therefore be less dense), but it would only be the first few litres pumped that would be affected. Most of the fill-up will be with gas at the temperature of the underground tank, and this temperature is never far from 15 degrees, which is what the pump uses as a measurement sample.
As well, even if the temperature were significantly different, the benefits are small. According to this table from Measurement Canada, the benefit is in the order of 2% for gasoline and 1% for diesel, for a difference of 15 degrees Celsius. And that is considering only the temperature of the gasoline, not that of the ambient air. Yet another myth shattered.
Do you know any urban legends with an environmental angle? Post them here. This is the right place.
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