Fuel plant housing top-ranking German car manufacturer (10)
I believe the answer is:
propellant
'fuel' is the definition.
(propellant is a kind of fuel)
'plant housing top-ranking german car manufacturer' is the wordplay.
'housing' indicates putting letters inside.
'top' says to take the initial letters.
'german car manufacturer' becomes 'opel' (I've seen this before).
The initial letter of 'ranking' is 'r'.
'r'+'opel'='ropel'
'plant' placed around 'ropel' is 'PROPELLANT'.
(Other definitions for propellant that I've seen before include "explosive" , "driver" .)