A surprising observation on fuel consumption

[Wildoskar]

I appreciate this is far from scientific but I find it interesting all the same. For nearly 4 years I've religiously used BP Ultimate Diesel in my XC60 D5 Auto. Although I can achieve well over 45mpg on good runs (once managed 55), my general average (mainly town and sub 20 mile journeys) tends to be around 32. About 4 months ago my local BP garage defected to Shell so I reluctantly switched to their equivalent as I wasn't prepared to waste fuel or time driving to the nearest BP. Over a 2 month period, my mpg dropped to around 30. I've never used supermarket fuel (don't have a good reason why not, I just haven't) but the Tesco fuel save proved to be just too tempting (14p to 18p a litre saving on average) so I took the plunge. To my amazement, over the last 2 months my mpg has increased to just under 36 (journey profile the same).

I've no explanation for this, I don't drive particularly aggressively but I don't dawdle around either, the car is just 4 years old with 58K on the clock and has been serviced each year. I'm now waiting for it's replacement, another XC60 - due in about 5 weeks.

[Harvey1512]

Some people are quite obsessive about their dislike of supermarket fuels but as the fuel they sell is turned over so quickly the quality is easy to maintain. Worry about the fuel station with no queue as that has more potential for problems.

Who knows is the answer. Your car may just suit that particular fuel better, your next car may prefer Shell. Shell super duper will have extra cleaning additives put in by the tank driver at the depot but the supermarket fuel you are using will actually draw from the same source so the actual fuel is identical bar the additives. Smile and enjoy the saving + extra mpg.

[wimorrison]

so it was you who has stolen the mpg from me

over last couple of months my mpg has gone down, same car, same fuel (Sainsbury) and same journeys

I was at a loss to explain this but I am now happy as it appears to have gone to a good cause

[volvoid]

schcool holidays - less traffic - easier driving - warm weather
all helps a bit

[simonjedrake]

Originally Posted by wimorrison

so it was you who has stolen the mpg from me
over last couple of months my mpg has gone down, same car, same fuel (Sainsbury) and same journeys
I was at a loss to explain this but I am now happy as it appears to have gone to a good cause

Ian - bet the above reduction have something to do with you change in driving patterns with your wrist in plaster over the last month or so - a lot more shorter journeys rather than longer work related trips!

[wimorrison]

Now why didn't i think of that?

I wondered if it was because the car was heavier as it was carrying the cast in my arm also but your probably right, it was actually my right foot that was heavier!

[S60Chris]

Turning the AC off seems to help too.

Averaged 49mpg on my way into work the other morning - 20 miles, mostly dual carriageway.

It's normally around 43/44 so seemed to make a difference switching AC off.

Overall average is much lower though - the work commute is just quite an economical run as it's normally dual carriageway 55mph...

[8ig steve]

My 2014 D5 AWD Geartronic has always returned a poor 37 mpg on a motorway run travelling at the legal limit.

This week I have been working in Devon (225 miles from home) and unusually for me I was keen to arrive as soon as possible so wherever possible I was making full use of the limit mph +10% + 2 mph rule.
To my surprise I averaged 41 mpg on the down trip. so I tried the same again on the way home and despite Friday traffic & roadworks still managed 39 mpg. I find this very weird as I have always felt there was a cliff edge on the fuel consumption at 70 mph and certainly did not expect an improvement by going faster

Could it be that there is some strange efficiency increase at 2500rpm