MFD MPG Lies

[DaveD]

It could be an issue with the high pressure fuel sensor or an internal fuel leak somewhere (injectors maybe?), there's no fuel spillage under the van, it starts immediately and there are no fault codes.

The reality is far more likely to be that the title of this thread is true.

 

[GruB]

Before I retired and bought the van my commute was on average 45 miles per day in total. I had to change my diesel car after being rear ended and went down the PCP route and tried a Toyota Aurus Hybrid, then another and then a Yaris Hybrid. In those 7 or so years I really understood the benefit of feathering the pedal and my fuel economy was amazing. My slower driving was a constant family joke.

When I drove my van home for the first time I looked at the MFD and was horrified to see 26mpg as the long term figure.
Currently I am at 36mpg however I do live in a Vale so most journeys have some gradient.
When I refill I will make sure I reset the odometer as I am curious about the theory behind this topic.
My 2020 T28 6.1 102PS does have a Bluespark Automotive Eco Booster box fitted, and that is supposed to increase fuel economy as well.

 

[Lee540]

With my speedo reading 70mph, the GPS on Waze also reads 70mph..

When I had my standard 16's, MPG would regularly average 45mpg, now on 19's, 37mpg but I don't really appear to be spending anymore on diesel.

2018 150 manual

 

[monty999]

Since owning my van ( last April) every fill to empty I have worked out the return and pretty much gets either 25-27. 68 plate 150 Tsi, now on just 7k miles. I do this out of curiosity really as, because I love everything else about the van ( apart from the front candle lights obviously), I’m not that bothered if it’s 25 or 30 mpg- it’s still a great van which I’m happy with whatever it returns. I did think about a remap for a bit more power/ torque/ mpg but a friend who works at Mercedes told me to try Shell V power, which I have filled up. The pick up is definitely more responsive but I will check after a couple of tanks if it returns better mpg which it should do. Unfortunately it’s so much more expensive, economically it doesn’t make sense but it’s an interesting comparison. We’ll see, and I’ll post the results when I get them for anyone interested.

 

[archersam]

I consider anything that is generated by VW computers to be a piece of fiction as if it was written by J K Rowling. I didn't personally buy a LWB shuttle and keep a bunch of things including a trolley jack etc in it to really care too much about its MPG.

 

[Crazymind]

For a petrol Transporter it’s excellent MPG. If I was to drive the Tsi it would probably seat at 20MPG .

 

[monty999]

To be fair I do drive it pretty steady but I have noticed it’s a bit more rapid off the mark with the V Power stuff

 

[jamesmack]

So this week from a full tank it says I've averaged 34.6mpg on the mfd, brimmed it back up this morning and it's worked out 33.6mpg when I've worked it out, pretty happy with that tbh! And that's from a 204 dsg sportline, consisting mainly of city and countryside driving

 

[GruB]

For the record - I too bought our camper for the fun of it. I’m only anal about the MPG because of years of hybrid driving. Although I’m not a true spreadsheet type of guy I still find it interesting.
My father was an actuary and sadly he died before I could ask him the following question:

Using the same vehicle and same distance and gradient, what uses more fuel; travelling slower for longer or faster for shorter time?

 

[GruB]

To be fair I do drive it pretty steady but I have noticed it’s a bit more rapid off the mark with the V Power stuff

Did some work with Custom and Excise many years ago. A man whom owned several forecourts branded Murco was found to be adding water to the main tank to distill the fuel sold.

I was also told by them the grade of fuel varies depending upon the site of purchase. Supermarkets can give better prices because the fuel is not as high grade.

 

[dubber36]

Using the same vehicle and same distance and gradient, what uses more fuel; travelling slower for longer or faster for shorter time?

As speed increases, there is more air to push out of the way.

James May did a very good explanation about why a Veron Supersport needed an extra 300 horsepower to gain an extra 10mph top speed. The faster you go, the air gets effectively denser, therefore needing more energy to pass through it.

 

[ShooglyStu]

Using the same vehicle and same distance and gradient, what uses more fuel; travelling slower for longer or faster for shorter time?

Separating the question into two components - speed and gradient, then
* the amount of energy required to go up a hill is always the same, steep or not, fast or slow (ignoring air resistance), so the amount of fuel required will always be similar, depending upon the load at which the engine/transmission is most efficient
* the amount of energy required to cover a distance quickly is always more than when travelling slowly (due to air resistance). The difference gets bigger the faster you go. The amount of fuel used still depends on engine efficiency, so you might find that going a little bit faster uses a little less fuel, but a lot faster will always use more fuel

 

[monty999]

Separating the question into two components - speed and gradient, then
* the amount of energy required to go up a hill is always the same, steep or not, fast or slow (ignoring air resistance), so the amount of fuel required will always be similar, depending upon the load at which the engine/transmission is most efficient
* the amount of energy required to cover a distance quickly is always more than when travelling slowly (due to air resistance). The difference gets bigger the faster you go. The amount of fuel used still depends on engine efficiency, so you might find that going a little bit faster uses a little less fuel, but a lot faster will always use more fuel

So I believe the optimum speed for fuel economy is always used as 56mph, I think that’s what they always state on stats .

 

[archersam]

On my recent 390 mile round trip to Paris and back I only managed to do it on one full tank (smaller capacity version) and the MFD showed 30miles left when I got off the Eurotunnel.

 

[ginkster]

So I believe the optimum speed for fuel economy is always used as 56mph, I think that’s what they always state on stats .

It’s because one of the stats used is based on 90kph which is (was) a common speed limit on trunk roads in Europe (and close to our 60mph). If you want to hyper mile you need to go much slower to reduce the wind resistance.

 

[Huba]

My MFD is currently saying the average is 48.2mpg, this is on a MFD trip 2 of ~1500miles. That suggests 740 miles out of a 70l tank. I reset the odometer trip every time I fill up and just checked have done 255 miles with a range of 455 miles (2/3 of a tank left). That's pretty normal for me on my commute, winter / spring / autumn. Has always been similar figures. I have a 2018 102 5 speed. Tyres are van contact eco (50psi), which are rock hard ride but give better mpg (1-2) than the van contacts that were on before (even harder)

I'm interested to know if it is accurate as in the summer on my commute driving carefully regularly get just over 50 mpg. I usually fill up with range of about 170-200 and the trip odometer is usually near 500. I will calculate it more precisely to check when filling up, reading the above posts it suggest my figures are optimistic

When we're away in the van it drops to low 40s. Anything over 50mph and mpg drops rapidly in my experience

So this morning I filled up and worked out the mpg on mine and it was 41.6mpg (406 miles) vs 48.5 on the MFD (1600 miles) so at least on mine I can confirm the MFD is optimistic. Would say I've had regens in the 406 miles, a few short runs and a compressor fridge running occasionally (so charging the leisure battery), so it may be a bit lower than it could be

I'll continue to monitor, but suggests the 50 mpg I'm getting in the summer is likely more like 43-44 mpg

 

[DaveD]

I'll continue to monitor, but suggests the 50 mpg I'm getting in the summer is likely more like 43-44 mpg

Still pretty good for the size and weight of the vehicle!
One of my daughters used to have a Fiat 500 that did about the same MPG as your van!

 

[ShooglyStu]

I'll continue to monitor, but suggests the 50 mpg I'm getting in the summer is likely more like 43-44 mpg

Very similar to my experience. The question is not whether the actual MPG is good or bad, but why the MFD display is so wrong.
Over just 406 miles, your van has consumed 1.4 gallons (14%) more than the MFD thinks it has. That's not a "rounding error".

 

[Huba]

Very similar to my experience. The question is not whether the actual MPG is good or bad, but why the MFD display is so wrong.
Over just 406 miles, your van has consumed 1.4 gallons (14%) more than the MFD thinks it has. That's not a "rounding error".

I do wonder if the people getting higher figures (like myself) are driving in a way the on board computer isn't set up for and its skewing the figures, whether its a algorithm I don't know, and I am at the extremes of the bell curve it covers? I often coast into junctions, roll down hills and the like to increase mpg. Like others have mentioned on this thread I am infamous among friends and family for being the person who drives slow and does whatever I can to use as little fuel as possible.

The others who drive more 'normally' with faster acceleration, more normal use of the brakes, more urban commutes etc may fit the MFD equation better which is why their figures are closer, albeit lower

My speedo under reads by 4%, not sure if that effects it

It is something that needs flagging to customers really though, maybe it is I haven't looked

 

[GruB]

We are kindred spirits @Huba
I’m sure it stems from years of cycle commuting that was then reinforced driving a hybrid.
Not only do I receive a warm glow from coasting down hill I get the extra glow from often entering the turn at the correct speed and therefore save my brakes as well.