Citroen C5 2.2 Hdi fuel consumption

my 2.2hdi (2001 year) has done 68,000, i do a lot of motorway driving at around 70 mph and get approx 44mpg, if i drop it to 55mph i got more like 52mpg, around town it does around 40mpg. One thing i notice is the difference in fuel, I now never buy supermarket fuel now, that significantly reduces mpg on mine. I always use either shell or bp ultimate. More expensive (BP ultimate more so than Shell) but either are great and make a noticeable difference in power and mpg. It also runs particularly smoothly on these fuels.

Cheers for the fuel tip. I've always been a bit cynical about branded fuels - I live next door to Shell's Stanlow oil refinery, and all the tankers, whether they be Shell, BP, Texaco or Sainsbury's, all fill up from the same tanks. I was convinced, therefore, that they are all the same, but I'll give BP a try, just to see if it makes a difference. Thanks.

Building Regs Boy ( snipped-for-privacy@virgin.net) gurgled happily, sounding much like they were saying :

The base fuel is the same. The difference is in the additives.

what are the additives ? how and where are the additives introduced ?

genuinely interested.

. (-@-.com) gurgled happily, sounding much like they were saying :

What are they? If they told you, they'd have to shoot you... Trade secret... Seriously, they'll be detergents and other "stuff". But they'll vary from brand to brand, and probably (especially with diseasel) from season to season (anti-wax and the like)

They're mixed in, AIUI, at the time of filling the tanker. Matey shakes a packet of "Esso" in, then puts 50,000 litres of undeaded or diesel or whatever in with it. Finally, he picks the tanker up and gives it a good shake. Ready to serve.