# Fuel consumption variations



## Solwaybuggier (Mar 4, 2008)

We've just got back from Portugal - did about 5000 miles over 12 weeks.

What puzzles me is the mpg shown on the trip computer - which was 29.9 overall. I know you never trust a trip computer reading for mpg - but I'm assuming they are consistently inaccurate!

Living in the far NW of England, we do 350-400 miles in the UK, and over that journey the mpg reading was over 32 mpg, and rising. When we crossed into France it started dropping very gradually over the weeks. I've noticed a similar pattern in earlier years, as well.

Although there were a lot of shorter trips and hillier roads in Portugal, most of the journey down through France and Spain was on dual carriageways or motorways (similar to in the UK.) And I'm sure I wasn't driving faster or less economically.

Has anyone else had the same experience? It struck me it could be that diesel in the rest of Europe is less efficient (although where the premium diesel wasn't too much more, I was generally using it.) Or are the carriageways elsewhere "grippier"? 

Or is there yet another explanation?


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## siggie (Oct 2, 2010)

Maybe it was the added weight of all the beer and wine bought in France ccasion5:

:grin2:


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## Pudsey_Bear (Sep 25, 2008)

You got it right in the second paragraph, don't trust them, brim to brim reading is the only real way of knowing.


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## Solwaybuggier (Mar 4, 2008)

Kev_n_Liz said:


> You got it right in the second paragraph, don't trust them, brim to brim reading is the only real way of knowing.


I don't trust them - but not sure why they would be more inaccurate in one country than another!


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## erneboy (Feb 8, 2007)

Foreign van?


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## dovtrams (Aug 18, 2009)

I cannot understand looking at these so called computer readings; we all know they are not accurate. On a long trip ie 1000 miles just do a brim to brim and calculate. I do one at the start of the year and a few weeks after the annual service; 26/27 on a PHGV Voyager. Happy with that as the car I had prior to the mh did about the same.

Dave


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## 113016 (Jun 5, 2008)

I never even bother looking at the computer readings, the only way is brim to brim.
Driving styles considerably alter the mpg, rushing away from traffic lights, heavy braking, stop start. I always try to drive smoothly and try to keep the wheels moving, I hate having to stop at traffic lights!
Speed, gear changing, motorways or national roads all contribute, along with hills, or just moving the van a few times to go to the borne, and weight!
Just drive as smooth as you can!


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## Solwaybuggier (Mar 4, 2008)

Thanks all for the comments - but as I said to start with, I *know* the bloody thing isn't accurate - but as far as I can see it is consistently inaccurate! And I don't understand why the reading varies from start to end of the journey... I'm driving in the same way. No-one else find the same?

I did do the brim to brim reading thing at one time, but bluntly life's too short.


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## Pudsey_Bear (Sep 25, 2008)

Solwaybuggier said:


> Thanks all for the comments - but as I said to start with, I *know* the bloody thing isn't accurate - but as far as I can see it is consistently inaccurate! And I don't understand why the reading varies from start to end of the journey... I'm driving in the same way. No-one else find the same?
> 
> I did do the brim to brim reading thing at one time, but bluntly life's too short.


All I can come up with is that I think it's all based on a fuel flow sensor, and if that isn't spot on or as normal, you'll get a different story each time.


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## siggie (Oct 2, 2010)

No idea how accurate my trip computer is for average MPG for a tank of fuel, journey, etc as I never look at it. I do travel with instantaneous consumption displayed as I find it a good indicator of the optimal point to change gear or the most economical speed to travel at along a stretch of road. Even then it is only a very rough guide, more for information than anything else.


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## 113016 (Jun 5, 2008)

Solwaybuggier said:


> Thanks all for the comments - but as I said to start with, I *know* the bloody thing isn't accurate - but as far as I can see it is consistently inaccurate! And I don't understand why the reading varies from start to end of the journey... I'm driving in the same way. No-one else find the same?
> 
> I did do the brim to brim reading thing at one time, but bluntly life's too short.


Solway, I usually get better mpg on the M way to Dover, then it drops on the next bit to Rouen and onward towards Chartres.
I think the hills towards Rouen lower it and onward we have many roundabouts, with slowing and accelerating. That is the fuel killer along with hills!
Then you get the constant slowing for villages. Simple as that, and even if you are using dual carriageways, you will be coming off and on!
IF you really want to know, you need to keep a check at every fill up. We do this as I just like to know and we have plenty of time to do this, it gives me something to do:surprise:


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## Solwaybuggier (Mar 4, 2008)

Kev_n_Liz said:


> All I can come up with is that I think it's all based on a fuel flow sensor, and if that isn't spot on or as normal, you'll get a different story each time.


Could be - except that on 4 long trips it's always ended up coming out either 29.9 or 30.2 - so maybe inaccurate but at least consistent.


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## Solwaybuggier (Mar 4, 2008)

Grath said:


> Solway, I usually get better mpg on the M way to Dover, then it drops on the next bit to Rouen and onward towards Chartres.
> I think the hills towards Rouen lower it and onward we have many roundabouts, with slowing and accelerating. That is the fuel killer along with hills!
> Then you get the constant slowing for villages. Simple as that, and even if you are using dual carriageways, you will be coming off and on!
> IF you really want to know, you need to keep a check at every fill up. We do this as I just like to know and we have plenty of time to do this, it gives me something to do:surprise:


That could be it - although we did have the same pattern last year when we went to Holland (not many hills!) through Germany. But sounds plausible.


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## Revise (May 13, 2012)

I travel from Liverpool to Scarborough about 5 times a year. In my new van, Same journey, and same load and the same driving style. Even this varies and I can only think it is due to the weather and wind I only ever use Shell fuel regular diesel. All figures quoted from brim to brim. Kon-tiki 3.0 Auto

When going my worst has been 22.7 and my best has been and the best has been 25.9.
Coming back my worst has been 25.4 and the best was 27.9. 

I think the thing that effects you the most is the wind. Must be windier going.


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## bognormike (May 10, 2005)

with a hulking great white (normally) brick travelling along the same road, doing the same speeds, same traffic, etc etc you will get much worse fuel consumption when there's a headwind. Motorhomes are not as aerodynamic as cars......


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## powerplus (Oct 6, 2014)

my 2.2 says 32.4 over a 1500 miles 


but brim to brim its around 29.5 to 30.5

i think that is quite good considering the van weight is around 3.7t fully loaded

it is worth checking the mileage covered and also the speed and compare it to your satnav

my speedo is around 3 mph out at 60mph the odometer is pretty well spot on over 100 miles

barry


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## gaspode (May 9, 2005)

It matters not whether you measure fuel consumption by trip meter or refilling, the fact remains that it will always be an average figure.
The fact about averages is that they will always end up at around the same figure after a certain amount of data is input, the more data, the closer the average.

I'll wager that if you did 8,000 miles a year and took your average MPG figure for the year it wouldn't vary more than 0.5mpg from the figure you measured last year or next year given approx the same mileage.

Boggy is correct, the biggest influence on MPG is wind speed and direction, this was much more noticeable on our last M/H which was a high "A" class with a very blunt front end, a good tail wind would take 3 or 4mpg off the trip and a strong headwind would do the opposite.


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## 113016 (Jun 5, 2008)

Having been involved in MPG research of tear drop semi trailers, at the MIRA test centre, yes wind and air flow does play a part and not small, but equally driving style, and road type, speed and weight plays just as much a part.
It is a bit here and a bit there and the flow of the vehicle!


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## gaspode (May 9, 2005)

Grath said:


> Having been involved in MPG research of tear drop semi trailers, at the MIRA test centre, yes wind and air flow does play a part and not small, but equally driving style, and road type, speed and weight plays just as much a part.
> It is a bit here and a bit there and the flow of the vehicle!


I absolutely agree with all those points, but my observation on the wind was added for the simple reason that M/H drivers don't always realise if they have a strong head or tail wind. Because of this they'll travel a set route twice, using the same driving style at the same speed and wonder why they used a lot more fuel on one of the journeys. This is very often due to variations in the wind direction and speed and may provide an answer to the O/P question.

But let's face it, MPG is a minor consideration, you might as well spend the cash while you've got it. The kids will only crash it on a new BMW or something similar when you pop your clogs.:wink2:


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## 113016 (Jun 5, 2008)

gaspode said:


> I absolutely agree with all those points, but my observation on the wind was added for the simple reason that M/H drivers don't always realise if they have a strong head or tail wind. Because of this they'll travel a set route twice, using the same driving style at the same speed and wonder why they used a lot more fuel on one of the journeys. This is very often due to variations in the wind direction and speed and may provide an answer to the O/P question.
> 
> But let's face it, MPG is a minor consideration, you might as well spend the cash while you've got it. The kids will only crash it on a new BMW or something similar when you pop your clogs.:wink2:


yes, I agree, the mpg falls into insignificance when you weigh up the cost of a M/H, depreciation and running costs.
Our previous van returned an average of 29 mpg at 3500kg, our present van only 23 mpg at 4500kg, but on a long tour to Portugal, the difference is only about £130, which won't break the bank, and would not be a deciding factor on if we can afford or not!


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## Solwaybuggier (Mar 4, 2008)

gaspode said:


> I absolutely agree with all those points, but my observation on the wind was added for the simple reason that M/H drivers don't always realise if they have a strong head or tail wind. Because of this they'll travel a set route twice, using the same driving style at the same speed and wonder why they used a lot more fuel on one of the journeys. This is very often due to variations in the wind direction and speed and may provide an answer to the O/P question.
> 
> But let's face it, MPG is a minor consideration, you might as well spend the cash while you've got it. The kids will only crash it on a new BMW or something similar when you pop your clogs.:wink2:


That makes a lot of sense - prevailing wind is normally SW, so going to the tunnel it's cross-ish. But in France & Spain more likely to be driving into the wind (assuming prevailing wind is SW there?)

*But* would you not then expect to generally have tail winds on way back? (I quite accept prevailing wind doesn't mean it's always that direction.). And our mpg goes down (slowly) rather than up on way back...

I quite agree that mpg is not be all & end all, though - I'm just puzzled at variation.


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## Pudsey_Bear (Sep 25, 2008)

I haven't actually done a proper check on the last 2 vans we've had, too depressing really, and I'm more concerned with the overall cost and how many miles I get from a full tank, I drive at a sensible speed 50-60 dependant on conditions, no hard acceleration, and avoid braking at all if poss, anticipate the traffic lights etc, stay in a high gear as long as possible but avoid labouring the engine, clutch and gearbox.

I try to get 400 ish from a full tank in the van, 600+ in the car, sometimes I get a bit more, sometimes less.

http://www.ecodrive.org/en/what_is_ecodriving-/the_golden_rules_of_ecodriving/


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## Robell (Mar 13, 2013)

I use Road Trip LE on my phone (free part of the app) to keep tabs on the fuel used and mileage readings. It then shows me graphs of average mpg and fuel consumption. The mpg varies a lot on each trip, but the average value is not that far from what the computer in the van says. 

Rob


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## Leffe NL (Jul 14, 2015)

Solwaybuggier said:


> I don't trust them - but not sure why they would be more inaccurate in one country than another!


It's those European miles/gallon innit, inferior to the good honest British miles/gallon :wink2:


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## Leffe NL (Jul 14, 2015)

Grath said:


> I never even bother looking at the computer readings, the only way is brim to brim.
> Driving styles considerably alter the mpg, rushing away from traffic lights, heavy braking, stop start. I always try to drive smoothly and try to keep the wheels moving, I hate having to stop at traffic lights!
> Speed, gear changing, motorways or national roads all contribute, along with hills, or just moving the van a few times to go to the borne, and weight!
> Just drive as smooth as you can!


While I use the instantaneous reading to verify what I'm doing as a guide, I drive exactly as you describe. Additionally on long rolling hills, I'll accelerate on the downhill and maintain on the ups.


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## Zebedee (Oct 3, 2007)

Can't understand the confusion here. You've only got to look at a map.

Going South is bound to use less fuel - it's downhill. :wink2:

Dave


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## fdhadi (May 9, 2005)

I use the Eco app on the Garmin sat nav. Set it up with the details of the MH ie avg fuel consumption around towns & motorways. When I stop to refuel I check how many ltrs the Garmin says I should need and find its very accurate. This also tells me my mpg.


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