Historic and Classic Vehicle Alliance spokesperson Malcolm Mckay warns drivers in different parts of the country may be receiving different grades of gasoline. In a common misconception, current E5 fuel does not always contain a predetermined five percent ethanol.
Instead, E5 fuel can contain between zero percent and five percent in each refill depending on the fuel supplier and the proximity of a garage to a refinery.
However, McKay warns some drivers could “suddenly” drop from a few percent ethanol to ten percent when the changes are made.
This could damage vehicles incompatible with the E10 believed to affect rubber and steel.
Talk to Express.co.uk, Mr McKay said: “There is a lot of confusion and there are areas that people don’t really understand.
READ MORE: Classic cars warned about compatibility with new petrol E10
“E10 is between 5.5 and 10%, so it’s not exactly 10% and it will vary from country to country.
“Not just between different fuel suppliers and companies, in some areas they will buy fuel from someone else because they don’t have a refinery nearby.
“A fuel that’s E5 in one place with five percent won’t have ethanol in another part of the country,”
“So it’s a bit of a lottery.”
AA technical specialist Greg Carter also confirmed that ethanol levels often vary.
He said Express.co.uk: “Right now it’s called E5. For various regulatory reasons, they have to say E5, but in reality it’s more like 4 or 3.5%.
“When it goes to E10, it will be a low of 5.5 percent up to a high of ten percent.”
He added: “[E5] maybe no percent, it’s a pretty complicated industry.
“It depends on what the fuel industry is doing at the time.”
Classic car experts at Hagerty Insurance have warned that parts of historic vehicles could “perish faster” because of the new fuel.
They say the Department of Transportation tests identified a series of problems with the new fuel.
This included degradation of fuel hoses and gaskets, clogged fuel filters, damaged fuel pumps and corroded carburetors.
It is estimated that at least 600,000 cars will be incompatible with the new gasoline, with most models built before 2002 to be affected.