Real world fuel economy

So, looking into going back to a Company car.

Lots of decent low CO2 diesels that are good for BIK tax…

But what about real world economy???

The likes of VW, BMW, Alfa all hitting a good combo of performance and economy “on paper”. Looking at BM 318d, Passat / Golf
Bluemotion 1.6 / 2.0 etc

I saw the new lambo in the news of the screws today which apparently has an mpg of 20!! I was surprised to say the least!!

I’ve got a 2.0ltr 140ps TDCi mondeo and real world for driving up & down motorways and round town etc is 44.1mpg over the last 48,000 miles.

Don’t listen to anyone who comes on and quotes trip computer figures – they are usually wrong.

but not as wrong as the “official” figures 😉

I get approx 41mpg out of my Saab 9-3 TiD estate. I got about the same out of the BMW 320D I had before the Saab. And that’s based on miles recorded vs fuel in. Official figures for “combined” are 47-48mpg for both cars

My daily commute takes me from north of Bradford to south of Wakefield, invariably some urban and some motorway miles mixed in. If I lived nearer the motorways, I’d probably get a better return

BTW the Alfa 156 1.6 t-spark petrol car that I had before the BMW came out at about 33-34mpg on the same route. 400 miles from a tankful as opposed to 500+ from the two diesel cars

take the lowest number quoted ( urban ), and bank on that, and you won’t go far wrong.

Touran 1.9 TDi – 47mpg over the past 40k miles – meant to be 44.9mpg combined.

but not as wrong as the “official” figures

The ‘official figures’ are not claims of fuel economy. They are the results of a standardised test PURELY for comparison purposes, so you can compare different cars having been put through the same test. In theory. Most manafacturers massage the test but they pretty much massage it in the same way. It does NOT reflect real world driving, but what is worse is that it also does not show how the car reacts to different kinds of driving. Some cars are much more sensitive to driving technique than others and therefore could be further from the govt figures in real world depending on who’s driving. Those VW TSI motors are the worst apparently. Extremely difficult to match the combined figure on those no matter what you do.

Anyway: Prius (old style) combined = 61mpg, get 56-63mpg summer, 52-58 winter. Passat 2.0 TDI 2006 auto (pre common rail) get 45-50 winter, 48-55 summer (both figures trip computer, pump figures are within 1-2 either way typically).

Interesingly I got some Nokian WR G2 winter tyres on the Passat and MPG is now way better than previously. 10% higher than I would expect. Got 55mpg today on a long drive around the mountains, despite half of it being at 130kph (and some bits way above).

My 535i has a lifetime (+120k miles) average of 24.3mpg according to the computer – and usually 25mpg on real-calcs…

Based on computer readout, our S-Max 1.8 TDCi Zetec does about 46-48 on most stuff. Add in a few longer motorway journeys and it will creep up to low 50s.

Particularly interested if the claimed low 60s for some of the “tax eficeint” diesesls are achievable in real life situations.

Note that the V+ shell petrol does actually yield a better mpg – I get just over 50 more miles out of a tank in the last two alfas i have had. Other makes of ‘premium’ don’t seem to have the same effect.

The only trouble is it also yields better performance, so you have to guard against a heavy right foot eating up the improved fuel efficiency.

V Power petrol is higher octane and has some other additives including cleaning ones I think. Higher octane improves performance and economy IF a car is tuned for it which many sportier cars are, but otherwise not. The cleaning additives might make a different over a period of years, not sure.

V power (or BP ultimate) diesel however is different – it contains the standard cetane improver (same stuff as you buy in Halfords under the POWER BOOST!!!!oneoneone!!! labels) which unquestionably helps starting and smoothness, and should help with power and economy too although some folk don’t report it.

Incidentally it actuall works out cheaper overall to by the powerboost stuff seperately than to fill with premium diesel – the results are the same. Or you could just buy 2-ethyhexyl nitrate aka 2-EHN (which is what it is) without all the POWER BOOST guff. Available here for cheap, sold to people using veggie oil as diesel and thinning it with petrol.

’07 Golf GT Tdi has returned 43mpg according to the computer over the last 12k. Trips are 80% shortish country lane runs. Get it on a decent A road dual carriageway run and it does 47-50mpg not driven very economically.

take the lowest number quoted ( urban ), and bank on that, and you won’t go far wrong.

The claim for my Smart is around 84mpg, I’ve tried everything I can think of and the best I’ve managed in 15000 miles is 74mpg.

I’ve got a new Golf Bluemotion (1.6Tdi). The average over the first 3000 miles has been 48mpg (from the computer), not as good as I’d hoped for really. It gets driven on a mix of motorway journeys (mostly by me) and short hops (by my good lady). Best – 62.3 on a trip to Brum recently, worst was about 30mpg on my way to work when it was really cold (6.5 miles). I don’t think my good lady drives it with as much mechanical sympathy as I do, so that might account for the slightly lower economy! Hoping it will improve a bit as the engine “runs in” (if that even happens anymore!)

Interesting on the fuel types front. Always found that petrol cars showed benefit of the better grade fuels – both performance and economy.

Never noticed the difference with the diesel (except less sooty emissions).

I get better than official figures when trying to, and worse when not trying to. IIRC for my diesel the figures are 39 and 54 mpg. I’ve had as low as 37 and as high as 65, based on tank-tank refils.

Interesting on the fuel types front. Always found that petrol cars showed benefit of the better grade fuels – both performance and economy.

Personally never had an “economy” type petrol – when it got super the boost got cranked up and the economy went well down, but on my HDi using the new fuelsave seems to have added 1-2mpg on, but that could be lost in a statistical forest of other variables to be fair – impossible to tell from 2 tanks full.

Land Rover Discovery 3 – combined fuel consumption is 30.0mpg. Depending on how much urban driving I do, I hit this. I checked the OBC accuracy a couple of times (brim-to-brim) and have found it’s within 1mpg.

Depends on how you drive. If I just bellowed away from the line every time, cruised motorways at 85mpg all the time, and generally had a heavy right foot, I’d be on 22mpg.

I’ve also got a Passat TDI estate – offcial combined is 46.5 (I think), my average over the last 30k miles is in line with this. Drops a bit in winter, improves in summer.

Golf Bluemotion (1.6Tdi)… average over the first 3000 miles has been 48mpg. Best – 62.3

That’s surprising!! I had the VW 1.6Tdi engine down as a likely candidate…

Although a colleague recently had a Bluemotion Polo as a hire car and reckoned it was rubbish. 3 cyl diesel, very economical but desperately slow. His view was that being underpowered required it to be worked hard in any situation other than motorway cruising.

Yep, it’s surprised me too rkk. I have a very light right foot and do drive with a view to economy most of the time. As I hinted, I think my better half is the weak link – it’s a company car, so I use it on business trips which are mainly motorway runs, she uses it the rest of the time and that’s just ferrying the kids around locally.

It’s a nice engine though, much smoother than the previous diesels I’ve had – much more petrol like.

Although a colleague recently had a Bluemotion Polo as a hire car and reckoned it was rubbish. 3 cyl diesel, very economical but desperately slow. His view was that being underpowered required it to be worked hard in any situation other than motorway cruising.

Think there’s some truth in that. It’s very much driver-caused, but if your engine is under powered for your driving style you tend to run everywhere at full throttle which isn’t the most economical on most diesels.

We have a TDI Passat and a dci Clio, both are very close to trip mpgs, driven carefully but at/around the speed limit we see 46mpg and 66mpg as overall averages over a few thousand miles both on trip and (sadly) the cumulative spreadsheet. And upto high fifties and high seventies if trying to get the best mpg. Top so far is 86 from London to Devon!

V Power petrol is higher octane

but that can’t be the only thing in the equation as the other fuel manufacturers do higher octane fuels but they don’t have the same effect as the V Power. My mate is a cosworth nut and also has a Mitsu Evo and this is the same conclusion the driving ‘groups’ he is in has, they all use the V Power.

Getting really good economy is more subtle than simply driving slowly. Lower overall speed will help within reason, but slow acceleration doesn’t necessarily help. In a diesel, it’s a trade-off between how much air you compress that just gets spat out of the exhaust (when running at light ‘throttle’) and how much still-burning fuel exits via the exhaust valve (at high revs or high ‘throttle’).

It’s better ime to accelerate reasonably briskly to your desired speed then keep it there. Constant speed really really helps. Check out your instantant MPG reading as you drive. You can ease down on the pedal a minute fraction resulting in imperceptable acceleration and your instant mpg will plummet. I drive on crusie control wherever I can (traffic permitting) and it helps. Constant speeding up and down, even minutely really hammers mpg.

CK, a small displacement diesel run at closer to wot should be more efficient than a larger one run at less throttle because in a larger displacement engine you’re compressing air you don’t need, say 1000cc each revolution when the fuel you’re injecting only needs say 200cc. If you are only compressing 300cc of air then you’ve done less wasted work.

Do you agree? I know there are more factors like heat transfer to the cylinder walls, but I reckon it holds true to an extent. Which is why I guess a larger displacement diesel engine is less efficient run at the same speed in the same car than a smaller one.

BMW massively overstate their predicted fuel economy, to the region of about 40%. I have a 120d, book figure for combined journeys is 69mpg, it does 42. It’s normal according to the dealer, but even on a warm day, drafting lorries at 56mph, it won’t exceed 55mpg on the motorway.

My 2003 Passat used to be able to get 60mpg and it pisses me off to the extent that when I change cars, the next one won’t be BMW.

drafting lorries at 56mph

that sounds like fun 🙂

but that can’t be the only thing in the equation as the other fuel manufacturers do higher octane fuels but they don’t have the same effect as the V Power. My mate is a cosworth nut and also has a Mitsu Evo and this is the same conclusion the driving ‘groups’ he is in has, they all use the V Power.

I’ve spent a fair amount of time tuning my engine using various fuels and listening to the knock sensor output on headphones. Vpower is the only one that makes a noticable difference to normal octane fuel, the others are (IIRC) at least 1 RON number lower than vpower and strangely I never got any benefit from any other than vpower, which doesn’t make sense unless there’s something else going on, so I agree 🙂

BMW massively overstate their predicted fuel economy,

They’re not allowed to overstate it to be fair, that is what their car gets in the required test. However whether that test reflects real world driving is another matter. And whether they’ve tuned the ECU to work perfectly in the test but be naff elsewhere…. Bear in mind that the highway driving section of the test (used to get the higher number) is at an average of 40mph. What highways do you know that that’s the average on? 🙂

Also BMW’s are generally very heavy for their size, full of trick kit and safety gadgets – any acceleration trashes economy in them.

Also BMW’s are generally very heavy for their size, full of trick kit and safety gadgets – any acceleration trashes economy in them.

A mate was complaining yesterday that his 2.5lt BMW estate only averages 27mpg (3 series I think, 3 years old had it from new and it’s always been this bad) and his commute is a 15 mile trip with 65% dual carriageway. Not happy.

Even DC trips can trash economy if there is any traffic, you need to hold speed bang on – watch the fuel use when you just brush the gas to overtake and you’ll see it pegged at 0mpg for the entire duration lol. I know someone who had a 330d estate and got mid 40s all day every day, then moved to a 530d and found he’s averaging 30mpg, but nearer 20mpg if he’s in town or accelerating much! Ouch.

sharkbait – Member

Also BMW’s are generally very heavy for their size, full of trick kit and safety gadgets – any acceleration trashes economy in them.

A mate was complaining yesterday that his 2.5lt BMW estate only averages 27mpg (3 series I think, 3 years old had it from new and it’s always been this bad) and his commute is a 15 mile trip with 65% dual carriageway. Not happy.

Crumbs my 10 year old 520(petrol auto) tourer gets 32mpg

with all sorts of driving styles i worked out last week that i was getting an average of 50-52 mpg. Then theres the benefit of using veg oil at £1.06 a litre at the moment.Using old oil would be good but ive never set anything up for processing it. saving 27p a litre helps a bit though.

The car was quoted as having a range of something like 55-74mpg when i bought it.The 74mpg figure was about the best there was at the time,even compared to a lot of the smaller cars on the market. (1.9tdi 90bhp)

7000 miles in a Mondeo TDCI 130 has given me real world figures of 49mpg (although when my gf borrowed it she got this down to 43mpg! On a 300 mile motorway run! How I have no idea. Maybe she forgot there was a sixth gear…?). This is almost bang on the claim for ‘combined’ mpg – but in reality nearly all my mileage is what I assume would be classed as ‘extra-urban’ – trips up and down the motorway of at least 50 miles. Claimed extra-urban figure is 60mpg! Oh and the trip computer consistently spouts wildly optimistic nonsense.

Be interested to know what the ‘standard tests’ somebody mentioned actually involve…

with all sorts of driving styles i worked out last week that i was getting an average of 50-52 mpg. Then theres the benefit of using veg oil at £1.06 a litre at the moment.Using old oil would be good but ive never set anything up for processing it. saving 27p a litre helps a bit though.

All good if you don’t have a commonrail diesel, most modern cars do and will die in short order with veg oil, even blended.

BMW massively overstate their predicted fuel economy

No they don’t, they tell you what they managed to score on the standard tests. It’s NOT predicted fuel economy.

most modern cars do and will die in short order with veg oil

Not necessarily. Although it’s way risky if you do not know what you are doing or exactly what’s under your bonnet 🙂

Not necessarily. Although it’s way risky if you do not know what you are doing or exactly what’s under your bonnet

Well if you like forcing the wrong fluids through your micron-diameter piezo injectors at 22000psi, round your nice super high pressure pump with the wrong lubricant capabilities and for an extended period without testing, to save a few hundred quid a year, that’s fine – go for it 🙂 I’m not currently aware of any manufacturers who allow more than 30% bio D in their engines and maintain warranty, and bear in mind that biod and veg oil are not the same thing 🙂

I have a new E Class estate 250 diesel with the blueefficiency engine. My last tank got me an average of 31mpg (calculated, not computer), that’s mainly commuting and some motorway. I’ve had as much as 41 on a 260 mile round trip. Not expecting to get much better, but then it has large wheels and roof/ bike racks on too. This morning’s 80 mile run down the M1 from Leeds got 33.5, but was into a headwind all the way.
The Octavia vRS diesel I had before it usually got around 38-43 depending on the run.

I’m not currently aware of any manufacturers who allow more than 30% bio D in their engines and maintain warranty, and bear in mind that biod and veg oil are not the same thing

No, the legislations are a bit odd. VW used to certify their engines for 100% bio then suddenly changed their mind a few years ago. Best guess is people were using poor bio and VW were having to pick up the tab. Badly made bio will wreck an engine in no time.

Anyway like I say some modern cars will be ok in some circumstances but it is not recommended unless you are a) rich b) like experimenting and c) know a lot about it.

And yes I know RME is different from veg oil, I know a fair bit about this subject.

roof/ bike racks on too

That’s at least 5mpg right there. Quite possibly more.

I know, PITA taking them on/ off all the time. Really ought to when on long runs without bikes.

Driven shed loads of the VAG 1.6 litre diesels and I reckon I could easily get an average 75mpg out of ’em.

1.4 TFSI, not had to many runs in them but a recent one I managed 50mpg but it was seriously hard work, I’m talking very very light throttle inputs, drafting wagons and using the stop/start quite aggressively, it was only over 10-15 miles too.

Don’t really bother trying in the new 2.0 litres, dunno why, older 2.0 litres would struggle to get 44mpg in an A3 tho, ’bout 49mpg in a 1.9TDI.

I’d consider myself a bit of a sado/expert at this kinda driving tho, my last average fill on my T4 van was 43.2mpg….