Oil from car black until changed (9)
I believe the answer is:
lubricant
'oil' is the definition.
(I've seen this before)
'car black until changed' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'changed' indicates anagramming the letters.
'car'+'b'+'until'='carbuntil'
'carbuntil' is an anagram of 'LUBRICANT'.
'from' acts as a link.
(Other definitions for lubricant that I've seen before include "it has a smoothing effect" , "Oil or grease" , "What might have you well oiled" , "Substance used to reduce friction" , "Oil, for example" .)