A widely-shared Facebook post claims that ethanol is being added to petrol in order to make it evaporate more quickly, and that drivers are being “ripped off” as a consequence.
The post says: “Husband has just got home from his annual cpc [Certificate of Professional Competence] course - he's a heavy goods driver.
“He and a few other course attendees commented about the issue with fuel being used up at an alarming rate (ETA my mistake not ethenol [sic] or methanol to diesel) The instructor confirmed that methanol or ethanol is being added to petrol to make it evaporate faster.
“So no, we are not imagining things. The[sic] are ripping us off left, right and centre!”
Although it is true that ethanol, a renewable fuel made from plant materials, is being added to petrol, and it is true that this slightly reduces fuel efficiency, the government’s stated purpose in doing this is to reduce carbon emissions, not to make people spend more on fuel.
The RAC explains that because ethanol is made from plants, which absorb carbon dioxide when growing, this partially offsets the carbon emissions generated when ethanol is burnt in fuel.
What is happening to petrol?
Since September 2021, the standard petrol sold at pumps in Great Britain has contained 90% petrol and 10% ethanol (the change is set to take effect in Northern Ireland later this year). Known as E10, the fuel replaced the previous blend of 95% petrol and 5% ethanol which had been known as E5.
Ethanol also functions as an alternative to lead which was originally added to petrol to prevent engine knocking. Leaded petrol was banned in the UK in 1999 due to health concerns.
Announcing the introduction of the new, higher ethanol fuel, transport secretary Grant Shapps said: “Although more and more motorists are driving electric vehicles, there are steps we can take to reduce emissions from the millions of vehicles already on our roads – the small switch to E10 petrol will help drivers across the country reduce the environmental impact of every journey, as we build back greener.”
According to the Government’s own figures, the use of E10 is expected to cut emissions of carbon dioxide by 750,000 tonnes each year. This is the equivalent of taking 350,000 cars off the road.
The post suggests that some drivers find themselves achieving less mileage from their fuel than they used to.
This could be related to the switch to E10, because the new blend is less energy dense than E5, meaning that drivers will indeed see a slight reduction in efficiency.
Government guidance says: “Using E10 petrol can slightly reduce fuel economy (the number of miles you are able to drive on a gallon of fuel). You may see a reduction of around 1%, but it is unlikely to be noticeable in everyday driving.”
The AA says the reduction in economy amounts to around half a tank per year for the average vehicle. However, some drivers have complained that the change in fuel economy is far greater than this.
There is also some evidence that E10 may lose more weight through evaporation than standard fuels. However this is unlikely to have a significant effect on most people’s fuel economy. In modern cars, once the fuel cap is sealed, fuel which evaporates within a fuel tank does not escape but is made available for use within the vehicle as vapours, as we have written before.
Image courtesy of Why Kei