In today's Sunday Mirror, UK, there is a question being asked, not i30 but a Renault 1.9 diesel.
Question:
"Filled up at the supermarket petrol station and the average mpg on the computer showed 36mpg. Filled up at local Shell garage and fuel consumption increased to 48 mpg. What's going on"
Answer:
"Basically there is a quality difference between supermarkets and the major companies. This is due to different refining processes, using different detergents and additives. I'm amazed at the huge difference. It could have been a bad batch, so worth trying experiment again."
Has anyone else noticed variations in fuel consumption with fuel bought from different garages?