Dog whistle in part of American's car? (8)
I believe the answer is:
tailpipe
'part of american's car?' is the definition.
(US term for the exhaust pipe)
'dog whistle' is the wordplay.
'dog' becomes 'tail' (synonyms).
'whistle' becomes 'pipe' (I've seen this before).
'tail'+'pipe'='TAILPIPE'
'in' is the link.
(Other definitions for tailpipe that I've seen before include "Rear section of exhaust" , "End to an exhaust system" , "Car exhaust (US)" .)