Pile on to the jalopy? (4)
I believe the answer is:
heap
I believe this clue is a double definition.
'pile' is the first definition.
(synonyms)
'to the jalopy?' is the second definition.
('heap' can be a synonym of 'jalopy')
'on' is the link.
(Other definitions for heap that I've seen before include "pile-up" , "Wreck of a car" , "Mound, pile" , "car on its last legs" , "Unreliable old car" .)