Car, until changed, contains black oil (9)
I believe the answer is:
lubricant
'oil' is the definition.
(I've seen this before)
'car until changed contains black' is the wordplay.
'changed' indicates anagramming the letters.
'contains' means one lot of letters goes inside another.
'black' becomes 'b' (abbreviation as in pencil classifications).
'car'+'until'='caruntil'
'caruntil' with letters rearranged gives 'luricant'.
'luricant' enclosing 'b' is 'LUBRICANT'.
(Other definitions for lubricant that I've seen before include "Oil or grease" , "Substance reducing friction" , "E.g. oil" , "it has a smoothing effect" , "What might have you well oiled" .)