Question: what is the most fuel efficient diesel engine?
Answer: Kia Ceed 1.6 CRDi (Official fuel economy - 72.4mpg) ... 
Citroen C4 Cactus 1.6 BlueHDi (Official fuel economy - 70.6mpg) ... 
Vauxhall Corsa 1.3 CDTI (Official fuel economy - 78.5mpg) ... 
Renault Clio 1.5 dCi (Official fuel economy - 70.6mpg) ... 
Mercedes-Benz A Class A180d (Official fuel economy - 80.7mpg)