mpg query

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xbimmer
Posts: 43
Joined: Mon Oct 08, 2018 7:14 pm

Post by xbimmer »

I have run on supermarket diesel since purchase (over 6000 miles) and averaged 46mpg with up to 51mpg on long runs. Following advice I filled up with Shell V-power super diesel but surprisingly my fuel consumption has gone up - now averaging 38mpg with 42mog on a long run. Anyone any idea what may be going on? Nothing else had changed although admittedly I've only done another 500 miles so far.
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DarrenF
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Post by DarrenF »

I am confused - You say your mpg has gone up but the figures have gone down?
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EmPeeGee
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Joined: Sun Jan 26, 2020 3:30 pm

Post by EmPeeGee »

DarrenF wrote: Sun Jan 26, 2020 2:17 pm I am confused - You say your mpg has gone up but the figures have gone down?
???

If you had 46mpg and you now have 38mpg, your fuel consumption has increased. Exactly as described in the original post.
DarrenF
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Post by DarrenF »

EmPeeGee wrote: Sun Jan 26, 2020 3:33 pm
DarrenF wrote: Sun Jan 26, 2020 2:17 pm I am confused - You say your mpg has gone up but the figures have gone down?
???

If you had 46mpg and you now have 38mpg, your fuel consumption has increased. Exactly as described in the original post.
Sorry - was scan readying it.

I was told about premium petrol (no idea if this is true or affects diesel) is that if the premium petrol is not being sold enough and sits too long in the tank it loses its performance. A bit like a use by date and once it gets old it loses its performance.
XC40 T5 R-Design Pro in Bursting Blue with Convenience, Intellisafe Pro, Winter Plus and Xenium Packs and a few other bits. Ordered July'19 picked up end of Nov'19.
72 dudes
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Joined: Sun Oct 13, 2019 5:42 pm

Post by 72 dudes »

@xbimmer. Possibly winter diesel is having an effect along with the colder weather. Winter diesel is sold everywhere between November and March. That is quite a drop though.

@DarrenF. Not many places will have super unleaded sitting around in tanks for that long. I'm not sure that it loses its effectiveness anyway .
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xbimmer
Posts: 43
Joined: Mon Oct 08, 2018 7:14 pm

Post by xbimmer »

don't think so - the two journeys I made (North Wales to Nottingham) were on consecutive days - day 1 going east on supermarket fuel was 51mpg, day 2 coming home on (mostly) Shell V-power was 42mpg. I must admit the V-power diesel was VERY cheap (130.9p/l) compared with 123.9p/l for the standard Shell diesel which made me a bit suspicious, but it is a new station. Average over the tankful was just 38mpg.
Shall keep an eye on the figures for a while but now back on supermarket fuel (not enough miles yet to compare).
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FGC5074
Posts: 12
Joined: Fri Jun 28, 2019 10:49 am
Location: North West

Post by FGC5074 »

I have noticed a similar thing with my T3 auto. I usually buy Shell V power petrol and typically only get 35 mpg. On a recent trip I was forced to fill up with two tankfuls of "cheapo" petrol, and I found I got noticeably better consumption. The difference was not as extreme as what you have described, but it sounds like it's time for me to do some further experimenting.
xbimmer
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Post by xbimmer »

Thanks FGC5074, good to know that I'm not cracking up after all!
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xbimmer
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Joined: Mon Oct 08, 2018 7:14 pm

Post by xbimmer »

Now done 1000 miles since refuelling with supermarket fuel and guess what my consumption has decreased back to the original 46mpg. So if any of you want to improve your mpg go for supermarket fuel rather than superdiesel!
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hdasmith
Posts: 392
Joined: Thu May 10, 2018 7:16 pm
Location: UK

Post by hdasmith »

xbimmer wrote: Sun Jan 26, 2020 9:33 pm don't think so - the two journeys I made (North Wales to Nottingham) were on consecutive days - day 1 going east on supermarket fuel was 51mpg, day 2 coming home on (mostly) Shell V-power was 42mpg. I must admit the V-power diesel was VERY cheap (130.9p/l) compared with 123.9p/l for the standard Shell diesel which made me a bit suspicious, but it is a new station. Average over the tankful was just 38mpg.
Shall keep an eye on the figures for a while but now back on supermarket fuel (not enough miles yet to compare).
I don’t think they’re really comparable journeys. Who’s to say that day 1 wasn’t generally downhill and with the wind (less drag), and day 2 wasn’t generally uphill, against the wind. You need more than one journey to test the results. It also needs time for the higher octane to burn off anything that might have built up in the engine to become fully efficient. It might also take time for the engine to recognise the high octane fuel, and recalibrate itself accordingly.

For what it’s worth, I don’t use high octane because I don’t want to spend so much before seeing if there really are any benefits. Outside of Europe, our standard fuel is considered high octane.
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