The mystery of the petrol pump

[Deswilkie]

Curious if anyone else has experienced this...
Last season before a race meeting I filled up two 20ltr jerry cans at my local Tesco. Paid and returned home to finish off packing. It wasn't till I was clearing out my wallet of receipts (no bloody money left in there thanks to bikes) and noticed I'd been charged for more than 40ltrs. It wasn't just 0.2 or so of a ltr it was an additional 3.7ltrs. I hadn't pored petrol over the forecourt and the metal containers don't have any Houdini like hidden compartments. Anyhoo as days had passed I put it down to being a one off and didn't do many (if any events in the later half of the year) to judge it by.

Yesterday I fitted the shiny recently purchased beet exhaust to my ZXR and to check it over (find where it was leaking from this time) I decided to get some fresh water and fuel in it to fire it up. With 5ltr jerry can in hand I go to my local Shell garage and fill it three quarters(ish) full. 5.72ltr the I was charged for!!!!!. The till monkey could barely speak English so I've decided to find the details for their customer relations and get in touch with them, and Tesco to query this.

I'm curious though; with fuel at the cost it is (mostly due to tax) has anyone else noticed this? I expect the huge majority of people will blindly fill their car and pay at the till (myself included) but for what quantity who knows? We simply trust the pump.

[RedexRobB]

Assuming your 5ltr jerry can is actually 5ltrs, you have a case. but are you filing to the brim? As i suspect it wont be 5ltrs to the brim, rather than it will be more.

I dare say, a 5ltr, 10 ltr or whaterever size its advertised as will hold that many litres, plus a bit more.

[Ewetea]

For what it's worth - here is my opinion: Since petrol is a very volatile liquid, I would imagine that manufacturers of jerry cans allow a significant amount of extra volume to allow for expansion/conversion to fumes due to increase in temperature. Grabbing a figure from the air, if they allow a 10% increase on the stated volume, then a 20litre can will actually hold 22 litres filled to the brim. This is not an ideal situation since an increase in temperature could cause violent ejection of fuel when the cap was released, with potential dangerous consequences. I would imagine that there are very strict regs governing petrol stations and the metering of fuel, and that checks are frequently made - probably just by driving up to a pump and deposting an amount of fuel in a container that is later measured to ensure it is the correct quantity. Thus the check is not obvious, and can be done at any time. Before trading standards are contacted I would recommend that the exact volume of the containers be checked. As a final thought - my Kawasaki handbook recommends that the petrol tank is only filled to the bottom edge of the filler tube, presumably to allow for expansion.