Make energy-guzzling old car (6)
I believe the answer is:
create
'make' is the definition.
(I know that make can be written as create)
'energy-guzzling old car' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'guzzling' indicates putting letters inside.
'old car' becomes 'crate' (informal term for an old car).
'e' going within 'crate' is 'CREATE'.
(Other definitions for create that I've seen before include "Be the first to make (a fuss?)" , "institute" , "Make or invent" , "Make a fuss (colloq.)" , "Make, Porduce" .)