German inventor passes heads of English labs (6)
I believe the answer is:
diesel
'german inventor' is the definition.
(I've seen this in another clue)
'passes heads of english labs' is the wordplay.
'passes' becomes 'dies' (passes away).
'heads of' indicates taking the first letters.
The initial letters of 'english labs' is 'el'.
'dies'+'el'='DIESEL'
(Other definitions for diesel that I've seen before include "Motor fuel" , "Lorry fuel" , "Fuel used by heavy vehicles" , "Vehicle fuel" , "Type of fuel oil" .)