The most common and most likely answer to this crossword clue is the 8 letter word GASOLINE
I've seen this crossword clue in The Sunday Telegraph
G
A
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Buddy explains!

The straight part
We know that "Engine driver" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case engine driver = gasoline.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GASOLINE mean?
GASOLINE noun- A flammable liquid consisting of a mixture of refined petroleum hydrocarbons, mainly used as a motor fuel; petrol.
- Any specific kind of gasoline.
- Made from or using gasoline.