Amazed at Fuel Economy - (actual figures)

[slider955i]

i average 25 - 26 mpg knocking around with my lead foot LOL

[Golf-Fiend]

Just returned from a camping trip from down south to the far NW of Scotland and back again, covering over 1700 miles. Car was fully loaded with all our camping gear, roof bars with roof box fitted, two adults and two kids. Car packed to the gunwales. 2.0 TDi Elegance - Aircon on Auto.

Actual fuel consumption figures:

Motorway part of journey at a steady 70mph - 50mpg!

Scenic tour of Scottish Highlands (single track roads, up hills and down glens, also 'making good time' and 'pressing on' at times) - 45mpg!

I was amazed that there was not more of a difference between the two figures considerin the more varied terrain and driving conditions. But I was more amazed at how frugal the car was. Very happy bunny!

Just came back from the exact same trip again just over 2 years later. Had identical figures on the M-way trip of 50.6mpg (actual measured) on the motorway trip and 42.9 (actual) on the scenic trip part with a lot of up-n-downs. Also this time it was a little wet on part of that trip And the kids are bigger/heavier!.

Seems that's the limit for this car as between trips it has a new MAF and temp sensor and battery. Pretty happy with this though diesel at the top of Scotland was over £1.50 a litre!!!

[xreyuk]

I was amazed at the 1.6TDI when I did an aiport run recently.

4 people, and 4 cases at 20kg, and I still returned 60mpg on both directions at 70mph.

It's amazing sometimes, at other times it's frutrating as hell!

[M12MKD]

Have to say I've either not got to grips with mine or there is something wrong with mine. Never got more than high 40's.

Where as my old PD fabia I'd regular see 60-70mpg and low 40's around town.

[andyvee]

I think the trick is to stay in the max torque power band of the engine - on a PD140 that is approx 1800-2250rpm.

That is where the engine is at its most efficient.

It is all too easy to drive round in 6th at 1500rpm in a PD140, and the fuel economy would be better in 5th (or maybe even 4th) at that speed.

If you look at my signature, averaging 48.9mpg over 87 tank fulls. There is some variance though between low 40's to high 50's, depending on the time of year and type of driving I have been doing.

[Golf-Fiend]

I think the trick is to stay in the max torque power band of the engine - on a PD140 that is approx 1800-2250rpm.

That is where the engine is at its most efficient.

Yes, I base my driving on keeping at around 2000 rpm and not the speedo. This equates to about 67mph in 6th gear according to the satnav. The car seems quite happy at this rate and slight motorway inclines are not a problem. Slightly steeper ones and heavy traffic and I'll drop to 5th. Sometimes I get a bit bored and boot it a bit if I want to pass some lorry convoys of other ejits on the M-way.

On the twisty hilly part where it averaged 42.9 I wasn't going slow for most parts, only the truly scenic mountainy bits and single track roads. The rest was sitting at around 65-70 on the long empty A roads. Even fully loaded as we were, it still had more than enough grunt to do a fair bit of overtaking too! [big grin/]

[Web Ferret]

It is all too easy to drive round in 6th at 1500rpm in a PD140, and the fuel economy would be better in 5th (or maybe even 4th) at that speed.

Aye thats me, easily chugging at 1500rpm. Will try your advice for a couple of weeks and see if I can squeeze some more mpg.

[andyvee]

Aye thats me, easily chugging at 1500rpm. Will try your advice for a couple of weeks and see if I can squeeze some more mpg.

Problem is, there is enough torque at 13-1500 to still pull in 6th, but it is more efficient to do so at 1800-2000 I find.

[nickguzzi]

My current 1.9 L&K est averages around the high 40's pootling about into town. Gets better on a run, easy to show 60+. Last continental jaunt was in the 51-52 mark over about 3500miles. When I first got it, it was much worse, struggled to get in the 40's. Improved vastly after 4wheel alignment.

My first octy which I had from new was if anything slightly better, but I probably drove slower on the autobahn.

I smiled when someone said their car was run in at 1500miles. Mine was still improving at 20,000. Sold at 250 000, engine still a stonker.

[supa]

I have a 2.0.tdi 2005 ambience and i frequently get 62mpg at at steady 70mph and it still amazes me!!!

[Golf-Fiend]

I have a 2.0.tdi 2005 ambience and i frequently get 62mpg at at steady 70mph and it still amazes me!!!

Ah, but is this actual or what is displayed? Mine showed 58.9mpg when actual was 50-odd

[andyvee]

Mine showed about 60 when it was nearer to 52. I have since adjusted the Maxidot to be closer to actual.

[Wardy]

Yep, my Maxidot MPG was 14% optimistic before I adjusted it, based on my own brim-to-brim calcs.

I agree with Andy's findings on the optimum rev range. On some more leisurely trips recently I've tested this sort of thing out, trying a set speed in 5th and 6th and observing what differences appear in the instant MPG readout. Not particularly scientific I know, but it does show that the lowest amount of revs possible isn't always the most fuel efficient.

I don't use Fuelly but run my own spreadsheet and I'm averaging 47MPG over my life with the car. That I'm very happy with seeing as I don't tend to hang about and it spends a reasonable proportion of time on shorter trips in urban conditions. And it's not exactly standard either

[have to say that's almost exclusively on Shell standard and latterly 'Fuelsave' diesel as I have noticed negative effects on MPG with supermarket fuel and other brands - that's another thread topic entirely though, I know!!]

[dbayman]

I think the trick is to stay in the max torque power band of the engine - on a PD140 that is approx 1800-2250rpm.

That is where the engine is at its most efficient.

It is all too easy to drive round in 6th at 1500rpm in a PD140, and the fuel economy would be better in 5th (or maybe even 4th) at that speed.

If you look at my signature, averaging 48.9mpg over 87 tank fulls. There is some variance though between low 40's to high 50's, depending on the time of year and type of driving I have been doing.

I don't think it is quite true that driving between 1800-2250 will deliver the best mpg. Although the engine may be most efficient in terms of power produced versus rate of fuel consumption the amount of power produced well exceeds what is necessary to get for best fuel milage, (which is measured by distance covered versus rate of fuel consumption). Generally with a car this occurs at relatively low rpms in a high gear, at a relatively low power output. The pressure on the right foot as well as the gear will have the most influence on MPG.

[Wardy]

Generally with a car this occurs at relatively low rpms in a high gear, at a relatively low power output. The pressure on the right foot as well as the gear will have the most influence on MPG.

You're right, the best MPG will occur when you can do the least amount of RPM but critically - without labouring the engine.

That then leads onto your point about throttle pressure. You'll often find at 1500rpm in 6th (for example) you'll need more throttle pressure than you'd need at higher revs in 5th to keep a desired, constant speed. This can leads to increased consumption, despite being in a higher gear at lower revs.

[zeffania]

I wish I had 6 gears, miss the extra after going from the Fabia VRS to the pd105 Octavia. Next car will have 6 gears, vrs cr I would imagine unless I get a decent payrise and get a Superb instead

[andyvee]

You're right, the best MPG will occur when you can do the least amount of RPM but critically - without labouring the engine.

That then leads onto your point about throttle pressure. You'll often find at 1500rpm in 6th (for example) you'll need more throttle pressure than you'd need at higher revs in 5th to keep a desired, constant speed. This can leads to increased consumption, despite being in a higher gear at lower revs.

I agree totally. It is all to do with how much throttle you are using. If the engine is capable of producing twice the amount of torque at 2000rpm than it is at 1300 rpm, and you want to maintain a constant speed, all you have to do is overcome the total of the resistance (rolling and wind etc) to achieve that. That will equate to a certain amount of torque, which can be achieved with less fuel at 2000rpm as the engine is more efficient (or it wouldn't produce more torque). Plus, these engines are turbo, at lower revs you are off boost so a small change in resistance to overcome (ie a slight incline) can require a fair amount of extra right foot, whereas at higher revs it can be a only a small squeeze.

I know this is an over simplification, but try it at 50mph on a level road and engage cruise. You will see better fuel economy in 5th than 6th according to the trip computer.

David Vizard once wrote very lengthy articles about it in regards to getting over 50mph out of the BL A-series engine. I know that was a NA petrol, but there is a similarity in that you need to be running at the point where the engine is at the maximum thermal efficiency, i.e the highest percentage of fuel injected goes towards generating torque. There is an argument to say that if you can run at lower revs with higher thermal efficiency but inject more fuel you are actually more efficient, but on turbo charged engines if you are off boost they tend to be quite inefficient.

[dbayman]

The gearing in the 2.0tdi CR is quite high, I normally wouldn't change to a higher gear if the rpm is less than 1500 - change into 6th before that and you can hear/feel the car doesn't like it. Going up a hill unless your on a motorway and topping 70 forget all about 6th going up hill. Can't complain about the mpg though - its mostly high 50s tank full to tank full.

My mpg indicator also reads 10% high. My last car was a nissan primera 2.2tdi CR and it's mpg indicator was always 10% low so when I first saw the mpg indication on the Elegance I thought WOW then came back to reality when I did a fuel check !

[andyvee]

I used 1300 as an example, probably a bit on the low side :-)

It would be interesting to see if you can spot a dfference on a CR at 50-55MPH between 5th and 6th on a level road - I am convinced it is more economical in 5th on a PD at that speed - but I may be wrong!

I went out in the car with my dad (approaching 70) the other day for the first time in years, he was through the box and in to 5th by 40mph, convinced that was the way to drive, engine pinking away like mad!

Then again, he learnt to drive in the good ole days of high torque, higher capacity, low revving 8v engines! Give him a modern 16v small capacity petrol engine and he drives exactly the same way!

[drefaldwyn]

My 1.9 TDI PD (slightly "Sharked" - only VERY slightly!!) shows 66 ish mpg on the display but actual is a much more believable 59 (brim to brim).

Dave

Smooth as silk!

[andyvee]

The 'Shark' bit helps I find

[Paul90]

Yep, my Maxidot MPG was 14% optimistic before I adjusted it, based on my own brim-to-brim calcs.

Am I reading this right ?

Is it possible to somehow adjust or calibrate the Maxidot MPG readout ?

Paul

[wiilydog]

Am I reading this right ?

Is it possible to somehow adjust or calibrate the Maxidot MPG readout ?

Paul

yes but you will need a VCDS cable to do it

[silver1011]

MPG threads always make me chuckle.

The dash display is a guide, the only accurate way to measure MPG is manually by filling the tank and noting the mileage and litres of fuel used.

If you car is telling you that your average MPG is regularly higher than it's official combined figure its lying

[andyvee]

Or it was downhill all the way