Fifth Gear Science – NOT!

John Bentley on Channel 5's Fifth Gear motoring programme tried to do some science in this week's show, and gave a pretty good demonstration of why it's best not to let a thick TV presenter teach you science.

Today's top tip was to go buy your fuel in the morning, when the fuel is cold. The logic was that as fuel is metered by volume, then buying cold fuel (which will expand and occupy more volume when warm in your tank) will give you more for your money. He reckoned 60 p per tank fill, which he scaled up to £30 per year.

It's a good idea, but needs a bit of testing, if only becaue the fuel pump and metering manufacturer's are unlikely to be daft enough to let 60 p per tank (or £30 per customer per year) slip through their hands, nor are the petrol company's or tax man, who collects more than half the revenue that pours through the nozzle.

Reality is that the petrol is stored deep underground in large tanks. Go down more than a metre or so, and the ground temperature varies very little in comparison to the overground temperature. Victorians knew this and used to build ice-houses down there to store their food, packed with ice to preserve it during summer, and keep their ice frozen.
The idea also forgets that the metering mechanism will be cold too, and will have contracted (does that mean you get less if the fuel is warm?), so providing a degree of automatic compensation, and that's without considering the temperature/volume correction factors that the metering manufacturer will have built into the pump. This has to be the case, or the seller will fall foul of fiscal Weights & Measures legislation if they actually sell you less than the metered amount, and W&M DO test and measure the delivered amounts. (Yes, I was involved).

Ever wondered how Urban Myths get started? (Ask Fifth Gear).

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