Damn energy-guzzling old banger! (8)
I believe the answer is:
execrate
'damn' is the definition.
(execrate can mean to curse or damn)
'energy-guzzling old banger' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mcr).
'guzzling' is an insertion indicator.
'old' becomes 'ex' (prefix meaning former or onetime).
'banger' becomes 'crate' (I have seen 'old banger' mean 'crate' so perhaps 'banger' could also mean 'crate').
'ex'+'crate'='excrate'
'e' going within 'excrate' is 'EXECRATE'.
(Other definitions for execrate that I've seen before include "hate" , "Curse" , "Express great loathing for" , "Utter curses upon, detest greatly" , "Express hatred for" .)