A metal-plated American car of old (6)
I believe the answer is:
austin
'car of old' is the definition.
'austin' can be an answer for 'car' (I have seen 'old car' mean 'austin' so perhaps 'car' could also mean 'austin'). I'm unsure of the 'of old' bit.
'a metal-plated american' is the wordplay.
'metal' becomes 'tin' (tin is a kind of metal).
'plated' means one lot of letters goes inside another (plated can mean covered or coated).
'american' becomes 'US' (abbreviation for United States).
'a'+'tin'='atin'
'atin' going around 'us' is 'AUSTIN'.
Can you help me to learn more?
(Other definitions for austin that I've seen before include "Capital city of Texas" , "Engineer" , "Texan city" , "The capital of Texas (6)" , "State capital of Texas" .)