Sad old fuel went out (7)
I believe the answer is:
doleful
'sad' is the definition.
(I've seen this before)
'old fuel went out' is the wordplay.
'went out' indicates an anagram (I've seen 'going out' mean this (out can mean wrong or inaccurate)).
'old'+'fuel'='oldfuel'
'oldfuel' is an anagram of 'DOLEFUL'.
(Other definitions for doleful that I've seen before include "Sad-looking" , "Dreary" , "Showing great melancholy" , "Cheerless" , "down in the dumps" .)