Car radiator additive (10)
I believe the answer is:
antifreeze
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">car radiator additive</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for antifreeze that I've seen before include "which prevents ice damage" , "Winter radiator additive" , "Addition to radiator" , "Winter essential in engines" , "Liquid added to car radiator" .)