Car fuel (6)
I believe the answer is:
petrol
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">car fuel</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for petrol that I've seen before include "Liquid fuel" , "Fuel for road vehicles" , "Common motor fuel" , "Fuel for the internal combustion engine" , "Mineral oil refined as fuel" .)