Fuel Economy Reporting Thread

VincentVega

I saw a garage in Wolverhampton selling diesel for 103.9p a litre. Fortunately, where I fill up it's only around 94.9p.

Of course, with winter on the way, expect prices to go up, as consumption of oil for heating and the like increases.

For the record, I drive a '06 VW Golf 2.0 GT TDI automatic and manage around 520-550 miles on 50 litres or so of diesel. The on-board computer tells me that my average fuel consumption is around 52-54mpg, which isn't half bad (IMHO).

fizzypop

Just what's possible on a Renault Modus 1.5 dci.
Urban 62-65mpg, longer run 84mpg.
How? I kept max speed down to 50mph
Which makes me a BOF!

tahrey

^^^^ how do I get rid of this unhappy looking chap?

edit: :mad: I had written a nice long detailed post here. Took me like 15 minutes. In this time my login expired and it deleted the entire thing... not a great intro to the board

In any case
I'll back up the 'yes it does' argument in a more terse style than I originally intended (still, it's likely to be a bit bloody long as i empty knowledge and opinion on several things from my brain to the interweb). From my personal fuel logs and some occasional experiments (or extremes of driving from being either incredibly short of time or cash):

1991 Polo 1.0
Somewhat underpowered and undergeared but capable of reasonable performance (if you caned it!) and economy (if you pretended to be your nan) even so.
Typical everyday driving, almost aping the Combined Euro cycle method: 35-40mpg
Caning it (90mph for a long motorway run followed by city slaloms): 30mpg... once 29.9mpg (only a small change as it was regularly under stress just to keep up with traffic!)
Driving carefully: 40-45mpg, 50, even 55mpg on occasion
Purposely trying to stretch out a tank as far as possible (55mph, slipstreaming, engine-off coasting, etc): mid 60s!
Informative experiment: just kissed 70mpg.... 2x improvement, not bad eh!
That last one however was a one-off... It consisted of starting at a motorway service station, topping off the tank there, and doing a ~40 mile loop at a constant 45mph, back to the same place and topping off again. Left lane of the M6 all the way. Even though it was like 3am (having come out of work at a nightclub) I have rarely had a more worrying and tense hour's drive as every truck coming up behind suddenly realised - bloody hell, i'm coming up on that CAR a bit fast! and had to dodge into lane 2. It could be a lifesaver should I ever be caught short of petrol on a bank holiday, but it's seriously not worth it for everyday use, and I wouldn't dare on a single carriageway or busy 2-lane dualie. Explains why all those old people in Rovers pootle about so slowly however - they're pulling in 70mpg economy without having to buy a brand new Bluemotion VW!
Also coasting with the engine off & in neutral was a definite winner in this car - as top gear was so frantic (lots of engine friction even on over run!) and it didn't have PAS or any kind of worthwhile brake assistance... Strangely, fitting a longer legged 5-speed box when the old 4-speed started to make funny noises didn't seem to make an appreciable difference, even when cruising at 60... (2800 - peak torque - vs 3400rpm)

1998 Astra 1.6
A bit more of a real car rather than a shopping trolley with a roof, I do appreciate the extra space, solidity and thrust, for the price of a little more thirst and less parking spots!
Everyday driving as before: ~33-34mpg. Uncannily consistent. Can pretty much bank on how many miles to a tank if I can keep my driving style under control.
Caning it: 27 to 30mpg. There's less opportunity to make full use of the car's improved performance over the Polo, so this isn't as terrible as it could be. In the absence of speed limits and other traffic it'd probably be 25 or less with a similar brick-on-the-pedal style... Going 'fast' mainly consists of accelerating hard to whatever speed the guy in front is doing, then cruising normally at a safe distance til they get out of the way (overtaking? on our roads? get away )
Driving carefully: 35-40mpg... yeah... being conservative in this one is as economic as travelling on autopilot with the older car! But it's doable! This is also the figure for travelling long distances with the traffic on the motorway, as demonstrated by 39.x figures going birmingham <-> cornwall and south west wales in a chilled out but non-timewasting mood
Trying hard: Nothing over 46mpg yet... but that's still a >10% improvement! And it's also when both a/ going somewhere within a timescale b/ picking up a heavy object (cheapo private sale replacement VW 'box so I could sell the car..). Haven't had time/opportunity/patience/reason to attempt a similar hypermilage attempt in the Astra. Plus I don't want to die horribly under a HGV!
However I feel that, if I could actually find one, swapping in a decent 6-speed (lower/tighter first 5 gears for city, even longer motorway 6th) would have benefit for this car. It's weight, engine characteristics and long gears mean its really not comfortable - or economic - in the city.

Conclusion: Your choice of car is probably the most important factor as regards your ultimate economy, but how you drive can certainly add some useful percentage to it. In my case I think getting my life more organised would probably cut my fuel bills by a good £100 a year...

As regards the idea of using full thottle and shifting up at 2000... I know and support the general idea behind what they are saying (its half of the Prius wizards' "pulse and glide" method) but the details cause some concern. Some ponderables:
1/ That's going to labour the engine an *awful* lot. Once you head much down from peak torque towards idle revs (and this method will put you much towards the latter than the former when shifting into 2nd and 3rd, unless you wastefully slip the clutch) you need to back off the thottle to stop it knocking and shaking - and being inefficient and getting damaged. I used to drive like this, then I recognised the sounds coming from the motor were probably a good sign I was killing it (not soon enough though - new head gasket and rings time!)
2/ A typical fuel injection / ECU car will have alterable fuel and ignition maps, and some even have alterable air paths - and I speak just from the two I've personally owned and their variants, let alone the vast multitude of cars on the road... the VTEC-like shift from economy to performance mapping tends to come at very wide/full throttle settings (sometimes even with a kickdown-like switch that you can feel being activated thru the pedal) along with an enrichment of the fuel, advancing of the ignition etc, which will dump all over your attempt to be economic.
3/ As if road conditions in the UK even allow you to do this shifting up at 1500? Believe me... I've tried... and nearly rear-ended people into the bargain. Even those at the head of British traffic queues tend to pull away slowly, and the further back in the queue, the slower it gets as people allow a safety gap to develop before accelerating at their usual (sluggish) pace. The only time you could safely attempt this all the way to crusing speed in 4th or 5th gear would be if you were pulling into gaps on a main road (in which case, sod economy, get to speed immediately for safety's sake), or being 'lucky' enough to land at the stop-line at a red light. And then when you do, you'll either be so far below your torque band - or just plain slip up - that you nearly stall it or creep away with all the power that 900rpm can afford you.
4/ I can't remember my no.4, lucky yous

However, getting to the higher gears - which tend to require higher speeds to run comfortably (i can't really use 5th below 33mph, so that's my camera-baiting city cruise speed ) - as soon as possible is the core idea. A reasonably wide (upto ~80%?) throttle and use of the lower end of the torque, rather than upper end of the power band is the key here. Exact figures will vary by car, but for my own ones - 8v lower revving jobbies that pull nicely from just under 2k thru to 4k before getting asthmatic - i'd be looking more to cap it at 3k and keep it above 1.5k when lifting the clutch in the post-shift gear to best exercise this theory (they both still had reasonable, if not exactly strong pull right down to idle, when running right, but started to shake horribly). Examine your car's own figures and how it "feels" through the speed range, and apply a bit of sensible judgement.

Also, hello :beer:

chivas

Conor wrote: »

.
Most of which is attributable to the fact you can maintain a constant 55MPH whereas something will inevitably get in your way at 70 and require you to slow.

something: usually people driving at 55 mph lol!

Crabman

heapug wrote: »

Since I started driving in the early 1950s I have watched with interest a great number of 'miracle' fuel economy additives and gadgets come and go; and to my knowledge, none of them have worked, and certainly none have stood the test of time. So it's very unlikely that the stuff being so persistently peddled in this forum has any value at all. But let's just pity the poor chap that keeps on pestering us here, because it almost looks as if he really believes in it...

Fifth Gear tested a range of 'additives' last week - not a single one did what it said on the tin, in fact they seemed to have a slightly opposite effect :rotfl:

That's right... Fifth gear - the arsonists... :whistle:

trucker1964

i think the reasoning behind this is the block changing method
ie. you go up two gears instead of one hope this helps

ps cheers for all the other info :beer:

anewman

I must admit my complete lack of knowledge in this area, but my impression was putting the foot on the accelerator was what made the fuel go in, so there'd be no benefit from coasting at idle vs taking foot off the acellerator in gear. Perhaps the RPM is maintained by the momentum of the car rather than fuel combustion which would be the same at both idle (coast) and in gear?!

jeferey

I have tried the faster acceleration technique and it gave me slightly lower mpg, 45mpg this time! I still believe steady to brisk acceleration through the gears (no higher that 2000 - 2500rpm depending on your fuel and your particular car - there is no hard and fast rule here) will give you the best mpg as long as your ultimate top speed is no higher than 60mph. People think that going 75 - 80+ on a motorway will save them a lot of time but unless the roads are empty (like when!), I believe there is no point racing around like an idiot, accelerating then having to brake, etc. On various journeys, I have stuck to a constant 60 mph on the inside lane and been amazed at how often I catch up with cars that went screaming off. I arrive at my destination less tired and less stressed and usually not far behind and with a lot more fuel in my tank. The fuel consumption of most cars increases greatly above 60 mph.

Ash1984

I often make a effort to drive smoothly (is that a word?). I drive a 2.0l petrol mondeo, if I drive without thought and floor it when I feel like it and stay steady 70 on the motorway I get just under 400miles to a £57 tank of fuel (@ £1 a litre), If I drive steady 55 -60mph on the motorway and easy on the acellorator its not uncommon to get to 480 - 490 miles out of the same tank of petrol.

Sorry about the poor spelling.

jeferey

Ash1984 - Just shows what a difference it can make. 31.9 mpg compared to 39.1.
If you did 10000 miles a year, this would save you around £262.