Car one American can make (6)
I believe the answer is:
austin
'car' is the definition.
(I have seen 'old car' mean 'austin' so perhaps 'car' could also mean 'austin')
'one american can make' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'american' becomes 'US' (abbreviation for United States).
'can make' becomes 'tin' (I can't justify this - if you can you should believe this answer much more).
'a'+'us'+'tin'='AUSTIN'
Can you help me to learn more?
(Other definitions for austin that I've seen before include "Capital city of Texas" , "Engineer" , "The capital of Texas (6)" , "Texan city" , "State capital of Texas" .)