Heavy vehicle an expensive failure? (6)
I believe the answer is:
tanker
This clue is a double definition.
'heavy vehicle' is the first definition.
'an expensive failure?' is the second definition.
(something which tanks)
(Other definitions for tanker that I've seen before include "Oil-carrying ship" , "Large cargo ship" , "Oil-carrier" , "Vehicle carrying liquid" , "Bulk liquid carrier" .)