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Car Forum / UK Car Forums / General Car Topics (UK group) / May 2008Diesel MPG drop?
I've noticed a slight drop in MPG lately, and on a forum I read so have several others with diesel cars, as has my brother-in-law. Normally I'd expect slightly better summer MPG. Has anyone else noticed anything similar? Is there any connection with biodiesel in forecourt fuel? My usage patterns haven't changed. > I've noticed a slight drop in MPG lately, and on a forum I read so have > several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 4 lines] > Is there any connection with biodiesel in forecourt fuel? My usage > patterns haven't changed. I've only checked twice, but the mpg on my diesel Xantia seems to have dropped from a steady 44mpg to around 38. I'll check again when I fill up and let you know MIke P > I've noticed a slight drop in MPG lately, and on a forum I read so have > several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 4 lines] > Is there any connection with biodiesel in forecourt fuel? My usage > patterns haven't changed. I'm getting a noticable amount better than a couple of months back , though I am making a very conscious effort to drive more economically because of the huge rise in fuel cost  SignatureAlex "I laugh in the face of danger , then I hide until it goes away" >> I've noticed a slight drop in MPG lately, and on a forum I read so >> have several others with diesel cars, as has my brother-in-law. [quoted text clipped - 8 lines] > though I am making a very conscious effort to drive more economically > because of the huge rise in fuel cost I've tried to drive more economically too, but even doing that haven't managed over 50mpg by the fuel computer. Previously I've managed up to 55. >>> I've noticed a slight drop in MPG lately, and on a forum I read so have >>> several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 11 lines] > I've tried to drive more economically too, but even doing that haven't > managed over 50mpg by the fuel computer. Previously I've managed up to 55. 59.5 mpg on a 40 mile trip this afternoon SignatureAlex "I laugh in the face of danger , then I hide until it goes away" > I've noticed a slight drop in MPG lately, and on a forum I read so have > several others with diesel cars, as has my brother-in-law. Normally I'd > expect slightly better summer MPG. > > Has anyone else noticed anything similar? Yes, it's a bit strange I can hardly top 55mpg now, last summer I could hit 70, I was tinking it was just me having more fun and overtaking more. > Is there any connection with biodiesel in forecourt fuel? My usage patterns > haven't changed. I don't think there is much difference in the energy density of biodiesel, unlike bioethanol, and it's been in there for a good few years anyway. >>I've noticed a slight drop in MPG lately, and on a forum I read so have >>several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 9 lines] > > I don't think there is much difference in the energy density of biodiesel, About 10%, apparently, although I didn't spot anything discussing the properties of a mixture. >>>I've noticed a slight drop in MPG lately, and on a forum I read so have >>>several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 12 lines] > About 10%, apparently, although I didn't spot anything discussing the > properties of a mixture. Bio diesel only makes up a small percentage of what we get from the pumps so there will be less than 1% difference. > I've noticed a slight drop in MPG lately, and on a forum I read so have > several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 4 lines] > Is there any connection with biodiesel in forecourt fuel? My usage > patterns haven't changed. Sorry, nothing that is statistically evidence either way. My five and ten run trend is still picking up from the winter just as I'd expect. SignatureThe DervMan www.dervman.com >> I've noticed a slight drop in MPG lately, and on a forum I read so have >> several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 7 lines] > Sorry, nothing that is statistically evidence either way. My five and ten > run trend is still picking up from the winter just as I'd expect. The brother-in-law reckons he's seen a difference between brands. I'll keep monitoring it. >>> I've noticed a slight drop in MPG lately, and on a forum I read so have >>> several others with diesel cars, as has my brother-in-law. Normally I'd [quoted text clipped - 10 lines] > The brother-in-law reckons he's seen a difference between brands. I'll > keep monitoring it. About the time I had my Ka crash I upgraded my PDA's car cost application and it happens to track brand, location and type of fuel. I don't believe that there's a difference although my data would appear to be suggesting otherwise... it's too soon to tell either way. The data shows the average mph because if I flatter one type of fuel - say if I only bought BP Ultimate Diesel for longer than usual runs - you'd see higher mpg and mph figures. The data can't take into account the different winter / summer grades. Suffice to say I've only filled up with Total over the winter. And sorry for the format issues, this report is generated by my PDA... Brand Type Fills MPG MPH ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph BP Ordinary, 8 fills, 50.2 mpg, 38.9 mph BP Premium, 6 fills, 51.0 mg, 38.1 mph Shell Ordinary, 44 fills, 49.8 mpg, 37.9 mph (my control fuel, 'cos I use Shell the most often) Shell Premium, 8 fills, 49.7 mpg, 36.5 mph Tesco Supermarket, 3 fills, 48.8 mpg, 37.3 mph Total Ordinary, 3 fills, 47.4 mpg, 36.2 mph Overall with 75 fills, 49.8 mpg and 37.8 mph, 43,195.6 miles, 714 days, £3,928.21. For Premium, that means BP Ultimate Diesel or Shell V-Power Diesel. The 9-3 is currently running on Total's premium diesel, Excellium. No data for this just yet. The data above might suggest that Shell V-Power Diesel is slow and thirsty. :) It just means that over these tanks the Saab spent longer in the city. BP Ultimate Diesel appears to be more economical if you believe that returning 51.0 is statistically significant against 49.8. It isn't. I need another few years worth of data first! ;-) SignatureThe DervMan www.dervman.com > Brand Type Fills MPG MPH > ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph [quoted text clipped - 8 lines] > The data above might suggest that Shell V-Power Diesel is slow and thirsty. > :) It just means that over these tanks the Saab spent longer in the city. I would look at you Shell Ordinary fills and see if they do support the apparent trend that your mpg is proportional to your mph. And then you can conclude that Tesco has too much bio, and the premiums are better. >> Brand Type Fills MPG MPH >> ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph [quoted text clipped - 13 lines] > apparent trend that your mpg is proportional to your mph. And then you can > conclude that Tesco has too much bio, and the premiums are better. Maybe: but three runs isn't enough to be statistically significant. 40 runs, maybe... SignatureThe DervMan www.dervman.com >>> Brand Type Fills MPG MPH >>> ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph [quoted text clipped - 16 lines] > Maybe: but three runs isn't enough to be statistically significant. 40 > runs, maybe... Looking at your figures, try averaging 100mph for a while, will save you a fortune. ;) >>>> Brand Type Fills MPG MPH >>>> ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph [quoted text clipped - 19 lines] > Looking at your figures, try averaging 100mph for a while, will save you a > fortune. ;) Heh :) Might be possible; the 9-3 is quoted as being 121 to 126 mph, depending on your source. Either way 125 is ~max power engine speed. I suspect acceleration is woeful over ~80 or so. SignatureThe DervMan www.dervman.com > >>> Brand Type Fills MPG MPH > >>> ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph [quoted text clipped - 19 lines] > Looking at your figures, try averaging 100mph for a while, will save you a > fortune. ;) Slower average speed suggests more stop-start driving. For the record, I've had a notable improvement in the MPG from my Passat since the weather has warmed up, and this seems to have been the case with most of the diesels I've had over the past few years. I believe they have to blend diesel to a different formula to ensure it doesn't solidify in colder weather so this might partly explain why I've generally seen less MPG in winter time than in summer... although the need for things like the lights / rear heated screen / heater fan etc, to be on more in the winter months might be a factor as well. -- JackH >>>>> Brand Type Fills MPG MPH >>>>> ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph [quoted text clipped - 30 lines] > -- > JackH Well, that's exactly what I've found before now. >>>Brand Type Fills MPG MPH >>>ASDA Supermarket, 3 fills, 50.2 mpg, 39.0 mph [quoted text clipped - 16 lines] > Maybe: but three runs isn't enough to be statistically significant. 40 > runs, maybe... If those 40 runs all come within 1% of 0.77 gallons/hour, and the BP ordinary ones do too, but the premiums always come out within 1% of 0.74 gph then the 3 runs can be significant. (Tesco is OK on a closer look). > I've noticed a slight drop in MPG lately, and on a forum I read so have > several others with diesel cars, as has my brother-in-law. Normally I'd > expect slightly better summer MPG. Maybe you're useing the aircon, or the fan more in the summer? Wishful thinking perhaps :)
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