Figure11 Posted March 13, 2008 Report Share Posted March 13, 2008 I watched the Top Gear episode the other day where JC takes an A8 sootchucker to Edingburgh and back on a single tank of crude. A couple of days later I watch the discovery channel programme Mythbusters where there examined whether driving close behind a lorry would reduce drag and allow an increase in MPG. The results they got were quite suprising, maxing out at about 30% increase if memory serves. Anyway, on my routine run to Glasgow I thought I would give it a try. The plan was to stay at about 4 to 5 car lengths behind a big lorry or coach from Plymouth to Knutsford services about 265 miles. Currently I'm averaging 15.6mpg on mixed cycle and the best Ive seen to date with careful husbanding on a run across country was 19mpg and worst 10.4. So, 5 hours later I fill up with LPG at Knutsford with 31.1 on the dash display and an actual of 22.5mpg. A 44% increase over average! Not something I would routinely do but an interesting experiment. Mike Link to comment Share on other sites More sharing options...
LostKiwi Posted March 13, 2008 Report Share Posted March 13, 2008 Interesting.... but there is something about sitting at wagon speeds with all that power under your right foot that just doesn't seem right.... I wonder how much of that 44% was due to travelling at a reduced constant speed? I did a test a while back of cruising at 60 mph and managed to cover 120 miles of motorway at an average of 33mpg... but I nearly went to sleep in the process!!! Still... 33mpg from a 4.2 QS isn't bad! Link to comment Share on other sites More sharing options...
FBFsussex Posted March 13, 2008 Report Share Posted March 13, 2008 [ QUOTE ] I wonder how much of that 44% was due to traveling at a reduced constant speed? I did a test a while back of cruising at 60 mph and managed to cover 120 miles of motorway at an average of 33mpg... but I nearly went to sleep in the process!!! [/ QUOTE ] yeah sitting at 56mph will give you just about the best possible MPG. try it at the same speed without being behind the rigs i wouldn't mind betting theres barely any difference. that said if you ain't in a rush it just goes to show what a difference you can really make to your yearly fuel bill Link to comment Share on other sites More sharing options...
LostKiwi Posted March 13, 2008 Report Share Posted March 13, 2008 Just don't tell the government... they'll make us all fit speed limiters set at 56mph "to help the environment" ..... Link to comment Share on other sites More sharing options...
Figure11 Posted March 13, 2008 Author Report Share Posted March 13, 2008 [ QUOTE ] Interesting.... but there is something about sitting at wagon speeds with all that power under your right foot that just doesn't seem right.... [/ QUOTE ] I just put on the calming influence of classic FM! [ QUOTE ] I wonder how much of that 44% was due to travelling at a reduced constant speed? I did a test a while back of cruising at 60 mph and managed to cover 120 miles of motorway at an average of 33mpg... but I nearly went to sleep in the process!!! Still... 33mpg from a 4.2 QS isn't bad! [/ QUOTE ] Good point. I'm off to see Ian in a couple of weeks I'll give it ago as it's a 4am start and see what I come up with. Mike Link to comment Share on other sites More sharing options...
cruiser647 Posted March 14, 2008 Report Share Posted March 14, 2008 56mph? Which old knackered coach were you behind? I've never seen a coach sit at 56mph. Especially a National Express one, they usually fly along at upto maybe 70! Lorries? yeah 56. Link to comment Share on other sites More sharing options...
Ska Posted March 14, 2008 Report Share Posted March 14, 2008 15.6 mpg mixed cycle? My 2.8 isn't managing more than 18.5 these days around town but on the motorway its around the same at 33 mpg must take a look see at a few things under the bonnet when the sun comes out, otherwise whats the use of a 2.8 Link to comment Share on other sites More sharing options...
LostKiwi Posted March 14, 2008 Report Share Posted March 14, 2008 [ QUOTE ] 15.6 mpg mixed cycle? My 2.8 isn't managing more than 18.5 these days around town but on the motorway its around the same at 33 mpg must take a look see at a few things under the bonnet when the sun comes out, otherwise whats the use of a 2.8 [/ QUOTE ] I should point out Ska - that 33mpg was one of the most boring drives ever... More usually I get mid 20s (though at the moment I have a duff O2 sensor so its more often 22 on a good run ) Looking to switch out the O2 sensors next week (some arrived yesterday and even having been assured they were right for my car they weren't....) Hopefully that will improve the situation no end when they are changed (I'm doing both as a precaution). Link to comment Share on other sites More sharing options...
gibbo37 Posted March 14, 2008 Report Share Posted March 14, 2008 According to my in dash display I managed 38.4 mpg on a recent 100 mile trip to North London along the M4 and M25. I wanted to see how much I could get and drove fairly steadily at about 70mph apart from the 50 mph road work sections. I usually get about 34 mpg driving at my more usual 80 to 85 mph. I think that's pretty impressive for a big car. The car is a 2004 D3 3.0 ltr, non quattro. Mind you driving it around town and I'm lucky to get mid 20's !!! Link to comment Share on other sites More sharing options...
Ska Posted March 14, 2008 Report Share Posted March 14, 2008 [ QUOTE ] [ QUOTE ] 15.6 mpg mixed cycle? My 2.8 isn't managing more than 18.5 these days around town but on the motorway its around the same at 33 mpg must take a look see at a few things under the bonnet when the sun comes out, otherwise whats the use of a 2.8 [/ QUOTE ] I should point out Ska - that 33mpg was one of the most boring drives ever... More usually I get mid 20s (though at the moment I have a duff O2 sensor so its more often 22 on a good run ) Looking to switch out the O2 sensors next week (some arrived yesterday and even having been assured they were right for my car they weren't....) Hopefully that will improve the situation no end when they are changed (I'm doing both as a precaution). [/ QUOTE ] Thats what worries me! Both my O2 sensors are new! Will clean out my TB and MAF... that sounds wierd Link to comment Share on other sites More sharing options...
charlie61 Posted March 14, 2008 Report Share Posted March 14, 2008 [ QUOTE ] So, 5 hours later I fill up with LPG at Knutsford with 31.1 on the dash display and an actual of 22.5mpg. A 44% increase over average! [/ QUOTE ] so the fuel computer said you averaged 31.1 but the calculation on mileage V fuel used said 22.5, is that what you mean. when I had my 4.2Q the wife started using it to drive the 1 mile to work, over a 2 weeks I recorded 8 mpg, she refused to stop driving it so I got rid, now petrol is heading towards £6 a gallon I can't say I regret it, maybe when 4.2 diesels come down to 15k i'll get another Link to comment Share on other sites More sharing options...
Figure11 Posted March 14, 2008 Author Report Share Posted March 14, 2008 [ QUOTE ] [ QUOTE ] So, 5 hours later I fill up with LPG at Knutsford with 31.1 on the dash display and an actual of 22.5mpg. A 44% increase over average! [/ QUOTE ] so the fuel computer said you averaged 31.1 but the calculation on mileage V fuel used said 22.5, is that what you mean. when I had my 4.2Q the wife started using it to drive the 1 mile to work, over a 2 weeks I recorded 8 mpg, she refused to stop driving it so I got rid, now petrol is heading towards £6 a gallon I can't say I regret it, maybe when 4.2 diesels come down to 15k i'll get another [/ QUOTE ] That's right I think! The dash is based on inlet vacum I think so if I were on petrol I should be seeing 31MPG. When I filled with LPG I got the equivelent of 22.5mpg. I am currently getting a saving of about 35-40% on LPG. Mike Link to comment Share on other sites More sharing options...
mlillywh Posted March 14, 2008 Report Share Posted March 14, 2008 I ummed and ahhed before getting my A8 - petrol or diesel, petrol or diesel. In the end i worked out that given the miles i do, it was about GBP700 a year cash in my pocket if I chose the diesel, and the diesel would have a better resale value She'll do 45Mpg if I drive 60 or so - more like 38 at 80-85. Of course thats with the aircon off. The average over a few tankfuls of normal round town, motorway etc is 33.5Mpg every time But with diesel at 109.9 its costing 90 quid to fill up - that took some getting used to!! But that diesel rattle is always there around town - If I didnt do the miles, its petrol all the way - 4.2 minimum Link to comment Share on other sites More sharing options...
Figure11 Posted March 14, 2008 Author Report Share Posted March 14, 2008 Link to comment Share on other sites More sharing options...
bigtone Posted March 16, 2008 Report Share Posted March 16, 2008 Mine's a 2.8 Sport Nov 2000 with 64K miles now and I have had it for almost 3 years when it came to me at 28K. The MPG comparison between computer figure and actual is interesting and I have checked most of my cars over the last 15 years, with varying results. My first Jaguar XJR was a 1990 XJ40 handbuilt by TWR and was always spot-on when checking miles/gallons against the computer. It always averaged 20 until I had a custom non-cat exhaust built and fitted, and went up to 22/23 with much higher torque. A really good car. 2 BMW 730's gave varying results; the 6 cylinder car computer was always spot-on but the V8 was never right from the moment I got it, with poor consumption and a dreadful gearbox plus the computer used to claim 28mpg but the car did 21 at best. BMW are over-rated and over-priced, and always have been. My next car with a computer for fuel consumption was a 1999 Mondeo ST24 V6 business car for one year and 32K miles, and the consumption was always in line with indicated and actual at around 29. My A8 is pretty accurate actually in the 2 checks I have made and these have been for about a month each time, adding up petrol used, miles done and then comparing with the computer which was reset at the beginning. I did a check in autumn 2005 and averaged 28.2 actual which was within 0.5 of the computer that was at 27.7. I've just checked it again last month and am getting 27.5 which is dead on between both measures, over a mix of driving mainly (70%) in the Welsh lanes and the rest on the M4 and M5. A dedicated trip on the motorway with the cruise set at 75 invariably gives me 34mpg, although I too did a day out about 18 months ago up the M5 and M6 to Warrington and back at 70, when I got 37mpg over the day. These are bloody good cars and apart from changing fluids and tyres on time, they really do not cost anything in my experience. The only thing 'wrong' with my 2.8 Sport is front wheel drive, because long wheelbase cars do not suit it and Audi should have presented rwd as alternative to 4wd in the A8. The paradox then is that it is probably the only example of a quality car in the world with fwd, because there are no others anywhere. All true quality cars are either rwd or 4wd; only. Link to comment Share on other sites More sharing options...
Ska Posted March 16, 2008 Report Share Posted March 16, 2008 Look at the up side you don't have to haul the quattro system around which actually makes the performance more lively than some would think Link to comment Share on other sites More sharing options...
FBFsussex Posted March 16, 2008 Report Share Posted March 16, 2008 [ QUOTE ] The only thing 'wrong' with my 2.8 Sport is front wheel drive, because long wheelbase cars do not suit it and Audi should have presented rwd as alternative to 4wd in the A8. The paradox then is that it is probably the only example of a quality car in the world with fwd, because there are no others anywhere. All true quality cars are either rwd or 4wd; only. [/ QUOTE ] totally agree. its the downfall Link to comment Share on other sites More sharing options...
simonbrown Posted March 17, 2008 Report Share Posted March 17, 2008 I recon I get about on average 25 round town in my 2000 2.8 sport non quattro with 145K on the clock. On a run if im light of foot and stick to 70 34 MPG is quite a regular occurance. The computer on LPG of course gives garbage readings , but the maths gives about 27-29 on gas . Unfortunately at about 60-70 in fifth the engine seems a little rough and hesitant so much so I normally need to knock it down a cog to coax some life into it....it may need a MAF sensor cleanout or a new Lambda sensor ( I had one replaced 3 months ago )Its in for a service this week so will get them to sort. The boss is trying to get me to switch over to a company car as hes paying mw 40p/mile at the moment...naturally told him where to stick his proposal!! a Golf Diesel or a Focus after an '8 ...hes having a laugh Link to comment Share on other sites More sharing options...
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