Row about this writer's old American car (9)
I believe the answer is:
limousine
'car' is the definition.
(limousine is a kind of car)
'row about this writer's old american' is the wordplay.
'row' becomes 'line' (as in a row of things).
'about' indicates putting letters inside.
'this writer's' becomes 'I'm' (the person writing the crossword clues).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'american' becomes 'US' (United States).
'im'+'o'+'us'='imous'
'line' placed around 'imous' is 'LIMOUSINE'.
(Other definitions for limousine that I've seen before include "Luxury car" , "Large luxurious car" , "big car" , "Luxurious car (with a chauffeur?)" , "Form of transport" .)