Wear out car part (7)
I believe the answer is:
exhaust
This clue is a triple definition!
'wear' is the first definition.
(I know this)
'out' is the second definition.
(thesaurus)
'car part' is the third definition.
(I've seen this before)
(Other definitions for exhaust that I've seen before include "Car's waste gas" , "Gases ejected from an engine" , "Weary" , "lower part of estate?" , "Sap - piped emission" .)