TDI 140ps Fuel Consumption

[Bassman4u]

I purchased a new Passat Estate Sport 2.0 litre TDI 140ps in June this year and the fuel consumption averaged 46.6 mpg until October, when it has since averaged 42.1 mpg for the same type of usage and driving conditions. Does this indicate an engine problem, such as low pump pressure? The vehicle is now approaching 6000 miles and so should be loosening up. Interestingly, my previous three new B5 Passat Estate Sport 1.9 litre 130ps cars never averaged less than 52 mpg.

[gazza007]

I have always averaged about 43ish overall mainly shortish runs but some journeys have been as high as 60 on long steady motorway runs. I was being especially light-footed when price of diesel was high.
Recently been averaging 36 but it has been colder than normal for about the last 4 weeks and I've been using Tesco Diesel

[hallcyon]

Bought mine as used in September with 12000 Miles on the clock. My consumption is up cosiderably too, but as this used to happen with my previous car, which was a Mondeo, I put it down to the cooling weather. A colleague who still drives a Mondeo is complaining of the same thing.
I must use a lighter right foot than you too. I'm achieving low to mid 50's just now travelling around 25 miles a day. I was mightily impressed by the improvement over my Mondeo where I struggled to get over 40 mpg at any time of year, however my Passat is a saloon which might also contribute to the improvement.

[Motorway]

mine was new in march and through the warmer weather i was getting mid to high 50's but as the weather cooled late october it has now dropped to low to mid 50's. before this b6 estate i had a b5 estste and a similar drop was experienced. the one before was a b5 saloon and this was the same. in general this b6 estate is on the whole more economical than the last b5. on a par with the b5 saloon .

i have a friend in southern spain with a b6 estate and he is currently still getting high 50's so this shows it is weather related

[Dtwo]

I have had my 2.0 TDI 140 since July and due to the cost of diesel started monitoring how good my mpg was. I have also noticed a drop since the tempreature has dropped. I think it may have to do the tempreature rather than any problem with your car.

I remeber reading about some one saying that a car performs better in cool tempreatures as it can get more oxygen and then burns the fuel better. but not sure how true that is.

[drmartin]

My 140 DSG estate, 2006 with 112k on the clock, used to be down to 38-39, but was hammered everwhere. Today, whilst traveling up the M1, I was doing 55mph with cruse set, yes everything was overtaking me, but the thing managed nearly 67mpg! this was supported by the fuel guage being frozen in the same spot for hours.

Normally its just under 50mpg driving to speed limits etc. I guess this shows what can be done if speed is not important.

M

[Spudrig]

I remeber reading about some one saying that a car performs better in cool tempreatures as it can get more oxygen and then burns the fuel better. but not sure how true that is.

That might possibly have been me in another thread! :p I was suggesting that due to the colder temperatures, the air is more dense, so the turbo sucks in more air, thus giving better performance, but only when engine is up to working temperature. But, mpg will decrease in cold weather due to the engine taking longer to reach optimum temperature, as well as the extra use of the heater, heated mirrors, rear windows, seats, etc.

Hope this helps a little bit :D

[eko]

With the cruise control set at 75 mph on my 2.0 tdi I average about 50 mpg on the motorway. Without the cruise I sometimes go as low as 43 mpg. I have never managed anything above 53 mpg.

[aristotle]

Recently purchased 2008 model SE Estate (ex VW-demo) with 9000 miles and have tried to match VW mpg figures with and without cruise set. Best so far is still only 44.8mpg on 150 mile journey which was mostly motorway with cruise set at 75mph. Wondering if there is something wrong as previous car was A3 with same engine which always did 50+ even with low miles?

[Quatrelle]

Recently purchased 2008 model SE Estate (ex VW-demo) with 9000 miles and have tried to match VW mpg figures with and without cruise set. Best so far is still only 44.8mpg on 150 mile journey which was mostly motorway with cruise set at 75mph. Wondering if there is something wrong as previous car was A3 with same engine which always did 50+ even with low miles?

Was your A3 an estate, how does it compare weight-wise with the Passat, tyre dimensions etc? Remember also that if you purchased it recently you have only driven it in cold weather.

This is not a 'defence' of the Passat, just curiosity! I don't do a great mileage, and don't get into 6th all that often because of the nature of the roads around here. My consumption is around 44-45 also.

[dieseljames]

I get about 38mpg - but I do very little mileage and my journeys are only about 6 miles tops. I used to have a B5 passat and that was very dependent on having the correct tyre pressures - it was amazing how a small drop of pressure could effect the fuel consumption (going by the dash computer)

[Quatrelle]

...... but I do very little mileage and my journeys are only about 6 miles tops. I used to have a B5 passat .....

jcruse - Did you use your B5 for similar short journeys? If so, was it ok? I ask because it's generally thought that such short trips are ruinous for turbodiesels.

[dieseljames]

When I had the B5 I was doing the same mileage but heading 6 miles north onto Dartmoor so I avoided the commuter traffic and worked the engine more- whereas now I just sit in traffic most of the time heading into Plymouth. I do occasionally give it a run but not as much as I want to/ aught to. The B5 was great and my brother-in-law has it now, it had high mileage when I got it so I didn't worry too much about the few miles I was putting onto it. 140k+ and still going strong, (can you tell that I still miss it?!)

[henley_regatta]

I purchased a new Passat Estate Sport 2.0 litre TDI 140ps in June this year and the fuel consumption averaged 46.6 mpg until October, when it has since averaged 42.1 mpg for the same type of usage and driving conditions. Does this indicate an engine problem, such as low pump pressure? The vehicle is now approaching 6000 miles and so should be loosening up. Interestingly, my previous three new B5 Passat Estate Sport 1.9 litre 130ps cars never averaged less than 52 mpg.


I have a (from new) SE Estate 2.0 TDI 140ps with 8,000 now on the clock, so broadly comparable to you except I know how mine was broken in (gently!)

I've managed just over 50MPG on a ~250 mile trip once or twice (best was 51.9 according to my trip log spreadsheet. Yes, that is sad of me to record it, I know I know).

My average for trips over 50-ish miles is in the 45-49 range now, however I go long spells where the car's only used for around-town mileage and I always find the first longer trip after such abuse only gets in the 40-45 range.

I can positively identify trips where (2-3 PSI) lower tyre pressure made up to 5 MPG difference to the mileage.

Privately I rate any journey over 45MPG as "win" according to my own car cost break-even factors and by that measure I'm mostly ahead of the game and happy. You'll get people on here claiming 55-60MPG on some trips and I can only think they're driving at 50MPH and have very-well-broken-in cars with 20K+ on the engine. No doubt some of them will now pop up to disclaim this!

I should also note that if your taking your mileage from the trip computer, I've found doing tank-to-tank full comparisons I can be 2-3 MPG off (usually the trip computer is over-optimistic) although on my more recent fills it's been more accurate than this.

[aristotle]

Was your A3 an estate, how does it compare weight-wise with the Passat, tyre dimensions etc? Remember also that if you purchased it recently you have only driven it in cold weather.

This is not a 'defence' of the Passat, just curiosity! I don't do a great mileage, and don't get into 6th all that often because of the nature of the roads around here. My consumption is around 44-45 also.
Quatrelle, A3 was a 3-door Sport so was 300+Kgs lighter but was only wider lower profile tyres. Drove it to Belgium fully laden, family of 4 plus lots of luggage and it returned almost 49mpg for the round trip. That's the sort of figure I'd expect for the Passat on a long run ie 48+mpg rather than the amazing 52+mpg figures I've seen. About to replace some Dunlops with Michelins so hoping that should improve things a little.

[Quatrelle]

Quatrelle, A3 was a 3-door Sport so was 300+Kgs lighter but was only wider lower profile tyres. Drove it to Belgium fully laden, family of 4 plus lots of luggage and it returned almost 49mpg for the round trip. That's the sort of figure I'd expect for the Passat on a long run ie 48+mpg rather than the amazing 52+mpg figures I've seen. About to replace some Dunlops with Michelins so hoping that should improve things a little.
I wonder then if the answer lies in the 300kg difference and the fact that the Passat is bigger all round. I wouldn't think the three other members of your family and luggage would equate to 300kg? Perhaps another trip to Belgium is called for...

If you do a search for 'fuel consumption' in this forum you get all sorts of figures quoted. I've given up trying to match them. It will be interesting to see if the Michelins make any difference.

[hallcyon]

I've noticed a significant increase in fuel consumption with the cold weather. I suppose that most of you have too. It is always stated that tyre pressures are important too.
My car needed new tyres on the front last week (fitted on Friday) and I did not get chance to double check the pressures until today. I normally average 60 to 63 mpg on my 13 mile trip to work each day. In the cold weather this had dropped to around 57 mpg. With my new tyres it was down even further to 52. The tyres are at the correct pressures again now. I will check any improvement in the morning, but did note a slightly better consumption on a different route this afternoon.
On a recent trip from the UK to Brittany via Boulogne with 4 people (2 adults & 2 kids) and luggage; driving between 70 and 85mph the average consumption over 1300 miles was around 45mpg, which I thought was amazing.

[offhighwayman]

What Spudrig says is exactly right coupled with the fact that the density of air is higher in cooler temperature, thus creating a larger drag force and demanding more engine power for a given speed.

[Spudrig]

What Spudrig says is exactly right coupled with the fact that the density of air is higher in cooler temperature, thus creating a larger drag force and demanding more engine power for a given speed.

Sweet, at least I remembered some of my A level Chemistry :p

[Stuart W]

I wonder then if the answer lies in the 300kg difference and the fact that the Passat is bigger all round. I wouldn't think the three other members of your family and luggage would equate to 300kg?

Well 70kg is about 11 stones, thus they wouldn't need to be huge people to total over 200kg.

And even one medium sized suitcase could weigh 30kg, thus in total 200kg would be easily attainable, and if we're talking big adults and loadsa luggage then that could easily exceed 300kg.

On the subject of consumption generally I agree with you that it's difficult to reconcile some of the figures. In particular I find some of the 60mpg+ figures hard to credit, unless caused by freak conditions eg a strong tailwind.

From my own experiences I would say that sitting on cruise at 65 would show around 55 on the trip computer, cruising at 70 should still be comfortably over 50 but 75mph would nudge the mpg to below 50.

Of course, that's assuming a flat surface and zero tailwind - a long, slight incline might not be noticeable visually but could have significant effect on consumption.

Best way to compare consumption is perhaps to set cruise over a flat bit of road of at least five miles or so and reset the trip computer, do the same thing in the other direction to average out the distoring factors and average the two.

I think I posted some figures in this regard a few months ago, over what seemed flat roads, but the differences in consumption were quite marked, reflecting, I think, a slight incline in the road and the prevailing wind direction.

[Quatrelle]

The method of choice on here seems to be brimming the tank a few times. Because I do a low mileage and don't get a lot of sixth I don't expect too much. I use it mainly as an indication of the health of the engine etc. The last long autoroute trip I did was up to the Massif Central on the A75, and that has some serious hills. I didn't even check the mpg then - too scared!

VAG's use of the 2.0tdi engine in various cars does throw up some interesting comparisons though.

[gazza007]

I have always averaged about 43ish overall mainly shortish runs but some journeys have been as high as 60 on long steady motorway runs. I was being especially light-footed when price of diesel was high.
Recently been averaging 36 but it has been colder than normal for about the last 4 weeks and I've been using Tesco Diesel

Amazingly the temp today got up to 5.5 after about 6 weeks of temps between -7 to +2. My ave MPG for my usual lunchtime 10 mile run home & back has gone back to 42 so def cold weather related

[hallcyon]

On the subject of consumption generally I agree with you that it's difficult to reconcile some of the figures. In particular I find some of the 60mpg+ figures hard to credit, unless caused by freak conditions eg a strong tailwind.



I do my 60 MPG at 05:30 in the morning at 55mph, south on the M42 Junction 10 to Junction 5 on the M6. It is fairly consistent. One day I even achieved 70 MPG over the same route. Presently it's around 53 MPG on this 13 mile journey.
I return in heavier traffic on A roads and only achieve 48 to 50 MPG.

Over 5500 miles, including a trip to France I have achieved 46 MPG. I hope I have managed to upload my calculator spreadsheet (zipped)

[Stuart W]

The method of choice on here seems to be brimming the tank a few times.

Yes, that's certainly the best way to ascertain accurate fuel consumption on a long term basis, but that includes too many variables thus it's difficult to make meaningful comparisons between cars.

Thus probably the best way to compare cars is to use a steady speed on cruise on a motorway environment with as flat a road as possible and with calm weather conditions, and thus doing a two-way average can iron out any inconsistencies in that regard.

But, of course, the only way to measure the consumption on such a basis is using the trip computer, resetting it at the beginning of the stretch of road where the car is to be tested.

Of course, brimming the tank a few times is necessary to prove that the trip computer is accurate in the first place, but from my own experience and comments of others on here it would seem that the computer being 1-2mpg optimistic seems about standard.

[Stuart W]

I do my 60 MPG at 05:30 in the morning at 55mph, south on the M42 Junction 10 to Junction 5 on the M6. It is fairly consistent. One day I even achieved 70 MPG over the same route.

Fair enough, but I did say that it might have been due to freak conditions, and 55mph on a motorway almost qualifies as that?

Seriously though, it's possible to achieve phenomenal mpg by driving abnormally, thus I think your figures are perfectly plausible, but when someone said without qualification that they achieved 60 mpg then I assumed they were talking about similar driving to what other posters were stating, ie 70-75 mph on the motorway.

[daveo138]

It has been stated in numerous previous posts on the B5 forum that 'winter' diesel reduces MPG. I know that my B5 used to suffer in the winter.

I've only had my B6 since November. I'm sure it was averaging 45MPG initially, but I had some DSG problems and the dealer changed some settings which seemed to alter some of the up-shift points. I'm now averaging 41MPG with a lot of 75-80MPH motorway driving on cruise.

My B5 (manual) used to do around 50MPG with similar driving, although touring around French A roads at about 60MPH returned an average of 55+.

The trip computer on the B5 was about 2MPG optimistic, but the B6 seems remarkably accurate

[Quatrelle]

Just checked mine - over the last 3,500kms it's averaged about 42.5mpg, at an average speed of less than 30mph.

[jh71283]

I was about to state the same thing as daveo138 that remember around october, winter diesel gets delivered to the stations, and is less efficient than summer diesel due to the anti gelling additives.

[james_tiger_woo]

I've attached my full costs sheet - total MPG is 43 odd but that's mostly due to my country road driving of late (picking up the little one from MIL's house).

As you can see - my costs have been, well, pretty high, but pence per mile is 18p.

[BenR]

There must be quite a few factors, which increase consumption in winter. My wife has noticed it with her C1 Diesel, which has dropped from 63 mpg in summer to 58 mpg now.

More use of electric ancillaries.
Warming up and defrosting with engine running.
Cold and more viscous transmission oils, engine oil etc.
Anti-waxing agents in fuel.
and possibly:
Denser air and more resistance?

I have an old Land Rover 90, which returns 26 mpg whatever the conditions. However one hot summer weekend I drove it from Lancashire to the North York moors and back and was amazed to find I'd got 35mpg on the trip. I put it down to a long drive at a steady 60 mph and above all to the various transmission oils (gearbox, transfer box, diffs, wheel bearings) running hot and therefore less viscous.

[Quatrelle]

Ben - the first ones definitely, the last one probably not.

imo, the 'denseness' would increase the engine's performance enough to balance out any possible increase in air resistance.

[Spudrig]

imo, the 'denseness' would increase the engine's performance enough to balance out any possible increase in air resistance.

Thats my theory too Quatrelle, I tried to explain it on another thread (it might actually be on this one, come to think of it!) using my partially remembered A Level Chemistry :p

P.S. Just had a quick look and it was earlier in this thread :p

[BenR]

Hmmmm. Fascinating techy question. We need a motor engineer to work this one out!

While we're at it, what effect does atmospheric pressure have on engine performance and wind resistance? At its most extreme, aircraft fly above 30,000 ft to find thinner air, don't they?

[henley_regatta]

Hmmmm. Fascinating techy question. We need a motor engineer to work this one out!

While we're at it, what effect does atmospheric pressure have on engine performance and wind resistance? At its most extreme, aircraft fly above 30,000 ft to find thinner air, don't they?

Don't bring Aircraft into it, especially not those flying above 30,000 feet. They're gas turbine engines and they have an entirely different set of performance metrics to optimise (for instance: the faster you go in a Jet, the more power the engine develops. If you're stationary, technically speaking the engine has 0 horsepower.... That doesn't translate well to one's 2.0 TDI which is perfectly capable of generating it's full quota of 140 or 170 PS at a standstill)

For piston aircraft, however, note that all of the performance records are for aircraft at low-level, where the air is thick. That's because the increase in power outweighs the increase in drag *for this engine type in most installations*. This has some bearing on what a car engine should do.

The basic issue for performance boils down to: cold air is denser, and you can therefore burn more diesel with 1 Litre of cold air than you can with 1 Litre of hot air (because there's more molecules to react with) and because you've reacted more molecules you've liberated more energy, and because you did that in a given time period you've generated more power on a cold day than you would on a hot day.

However, even ignoring the fact that this hot/cold difference - in temperate Blighty - probably only amounts to at most 5% density difference - I strongly suspect that any notional power increase (which you translate into improved consumption by reducing your throttle level for a given requested speed) is:

a) Mapped away for you by the ECU which wants to keep temperatures even on output to avoid overheating issues
b) Counteracted by the reduced calorific value of winter-grade diesel
c) Counteracted somewhat by the increased air drag on a cold day (due to increased density) - again, probably negligibly for cars at road speeds
d) Counteracted by everything being that bit stiffer because it's colder
e) Counteracted by you climbing in and switching the seats, windscreens and mirrors on to warm up on a chuffing cold day.

Having said all that, I strongly suspect that, outside of a properly controlled scientific experiment, nearly all of the above with the exception of b) is unquantifiable in practice, in terms of a real-world effect. So you're effectively left with "Winter Diesel doesn't have as much Ummph as Summer Grade" explaining the (bulk of) the decreased MPG when it's cold.

...And can I just say I enjoyed writing all that down even if you didn't enjoy reading it and even if I prove to be wildly wrong...:biglaugh:

[Quatrelle]

...And can I just say I enjoyed writing all that down even if you didn't enjoy reading it and even if I prove to be wildly wrong...:biglaugh:
On the contrary - very interesting.....

My 2p's worth, that moist air is best of all - on another thread I pointed out that water injection to boost performance has been tried on quite a few occasions.

I would also have thought that a turbo would compensate for most problems associated with less-dense air, especially with high-flying petrol-engined airplanes.

[henley_regatta]

On the contrary - very interesting.....

My 2p's worth, that moist air is best of all - on another thread I pointed out that water injection to boost performance has been tried on quite a few occasions.

I would also have thought that a turbo would compensate for most problems associated with less-dense air, especially with high-flying petrol-engined airplanes.

You're right - Water injection works a treat for boosting power in aero engines, both piston and turbine. There's two effects: firstly, it cools the air and makes it denser (more important for Piston engines), secondly it just generally adds bulk to a given charge of air (improving Mass Flow, which is a key performance metric for Turbine performance). It also made cool dirty black clouds out the back of B52s on water-injected take-offs: great if you're first off, not so great if you're 8th in the squadron scramble.

However, this was in the days before Computers started sticking their noses into the combustion process. I suspect that the ECU in a modern car would (via the total mass flow sensor) compensate for water injection and would scale-back diesel injection to keep temperatures the same - you'd perhaps see a slight reduction in consumption but I doubt you'd see an increase in power in an ECU-controlled engine just by pumping water into the inlet.

Slightly related: Aero engines originally (in the late 1920s) added Superchargers not for a total increase in power but to allow sea-level power to be generated at higher altitudes (by using the turbo-super-charger to increase ambient air density back to sea level density). With the increases in metallurgy etc, modern car engines are able to go above 1 bar without "bursting", so we get more power out of our cars thanks to the Turbo rather than the same power at the top of a mountain ;-)

[martin1810]

I think you will find that it's all about efficiency. Engines are very good at converting fuel energy into heat which is wasted, not so good at turning it into motion as miles per gallon. When it's cold , engines take longer to warm up and loose more heat during use, even with clever electronics. More heat loss equates to less mpg. Because engines are very inefficient, any drop in temperature will make mpg worse.