# MPG claims + petrol v. diesel



## kiwi (Jan 15, 2016)

I have been reading various MPG claims in the forum and can't compete! I have a Talbot Harmony petrol and only achieve low 20's - even driving carefully. Similar models with diesel I hear achieve over 30MPG. And yes, my tyres are pumped up, not all my driving is uphill, and I don't have the pedal to the floor (although she doesn't exactly perform like a Formula one!)


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## RichardHelen262 (Jan 15, 2016)

I have a sprinter diesel and only achieve low to mid 20's I don't know how these people with coach builds get mid 30's  but if it is only used for holidays does it really matter ?
You will have made the saving when you bought it as had it been a diesel the chances are it would have been more money to buy


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## Tbear (Jan 15, 2016)

kiwi said:


> I have been reading various MPG claims in the forum and can't compete! I have a Talbot Harmony petrol and only achieve low 20's - even driving carefully. Similar models with diesel I hear achieve over 30MPG. And yes, my tyres are pumped up, not all my driving is uphill, and I don't have the pedal to the floor (although she doesn't exactly perform like a Formula one!)



I have a Peugeot Boxer with a 2 litre petrol engine. I find it better not to work out my MPG unless I am on a long run with the wind behind me. It's a fully loaded van. What do you expect? A good service may help and a compression test may give a clue to why so low but I suspect removing weight is the only way to improve it. Failing that, ignore fishermans stories when it comes to mileage. 

Richard


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## antiquesam (Jan 15, 2016)

I used to have an app on my phone to give mpg on the van, which is a '95 Ford Transit chassis with a coachbuilt body and it stuck relentlessly at 23-24 mpg. When diesel was 135p a litre this was too depressing to look at, but isn't quite so bad at £1 a litre.


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## phillybarbour (Jan 15, 2016)

Low 20s on that era of petrol van would seem reasonable to me. Newer vehicles will do better but then depreciation is higher. If your vans tidy your on to a good thing overall so try just to enjoy it as that mpg is to be expected.


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## Deleted member 9849 (Jan 15, 2016)

I have a 2.8 diesel and the fuel economy is usually around 25 give or take 10% either way depending on driving conditions and terrain.I worry more about servicing and sourcing spares as it's very easy to pay over the odds for these.I try not to get too worried about mpg,I didn't get a motorhome for economy reasons,it's the lifestyle I bought into.


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## Siimplyloco (Jan 15, 2016)

We averaged 24 mpg this season fully loaded and traversing all sorts of terrain. Quite happy! When tugging with a 2004 Kia Sorrento we only got 21!
John


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## Teutone (Jan 15, 2016)

helen262 said:


> I have a sprinter diesel and only achieve low to mid 20's I don't know how these people with coach builds get mid 30's  but if it is only used for holidays does it really matter ?
> You will have made the saving when you bought it as had it been a diesel the chances are it would have been more money to buy



I can tell you how. They only drive with 50mph on the motorway.

I tried it on a trip where we had plenty of time to get to our destination. You can save by driving slow. But boy it is SLOW! I can't do this. On average we do 60mph and I am happy to pay the difference for the more consumption. We are not too bad, ours is a low profile with no overcab bed. I still manage 30mpg ish.
I found that weight isn't too much of a mpg killer, it's the aerodynamic. If you have a overcab bed your mpg will go up a lot for every 5mph you drive faster.


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## listerdiesel (Jan 15, 2016)

Gearing affects it as well, plus engine size etc etc., but as already said, the cost difference on fuel over a trip isn't really worth worrying about.

Towing our big trailer with the show engine loaded drops us down to 10-12mpg on hilly country, but the Discovery runs on LPG so costs aren't too bad.

The Mercedes is geared for 50mph running and will do 20-25mpg, but it is a 6-tonne van and has a 4.25 litre turbo diesel engine, built for comfort, not for speed  

Peter


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## ricc (Jan 15, 2016)

to get the mpg a diesel is capable off you need to understand the differences between the characturistics of petrol and diesel engines.
petrol engines have little torque (twisting power or grunt) at low revs so need to be reved to pull the skin off a rice pudding .
a good diesel produces near enough the same torque throughout the rev range , torque at 1000 rpm is near enough the same as at 4000 rpm .
what this means in practice is that at a given road speed you can be in a higher gear in a diesel.... the less revs the engine is doing the less fuel its burning.
in practice you can be changing up a gear at 2 to 2.5k rpm and not changing down till arround 1k rpm.

as a student many years ago we had a david brown engine on a dynamometer doing hp,torque and fuel consumption measurements at varying loads and engine speeds.  most of us got a bollocking for not being brutal enough on the high load/ low speed part of the test.... ie not loading the the engine to phutt phutt stall point at arround 500 rpm.   


another factor , probably not really relevent to motor homes is on short journeys a petrol engine gives abismal mpg untill its warmed up whereas a diesel mpg is pretty good even on a cold engine.

in short if you drive a diesel like a petrol , using high revs you wont get the high mpg figures.


dont forget fuel consumption is only one aspect of lifetime cost.  servicing costs and engine life span also have to be taken into account.

ive no experience of modern (under 15 year old engines) but historically youd expect a diesel to outlast 2 perol engines and the servicing costs to be lower on the diesel.   you didnt have ignition componants ,(spark plugs , leads distributor caps , consencers ) to routienly replace or adjust or fail on a wet night.


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## Teutone (Jan 15, 2016)

ricc said:


> ive no experience of modern (under 15 year old engines) but historically youd expect a diesel to outlast 2 perol engines and the servicing costs to be lower on the diesel.   you didnt have ignition componants ,(spark plugs , leads distributor caps , consencers ) to routienly replace or adjust or fail on a wet night.




these days I am more inclined to look at a petrol engine for longevity and low service cost than a diesel. Most modern diesel engines are around 2 liter capacity and turbocharged pumping out 150-180bhp! Fair enough, the economy and grunt are outstanding but to achieve this they are full of computers, sensors, recirculating system, coolers, filter and and and. Everything is stretched to the limit and if things go wrong you are either faced with a huge bill as a result of extensive fault finding (from replacing every sensor, filter etc from front to back) or a huge bill from the engine going pop and it's not economical to repair it because all the tech around it needs to be replaced same time.

So if your "old" diesel is a little bit more thirsty than all these new high tech diesels, it may well not be more expensive in the long run.

PS something about tourque. There is no replacment for displacement :wacko: (or a turbo charger.....)


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## Siimplyloco (Jan 15, 2016)

ricc said:


> SNIP
> 
> ive no experience of modern (under 15 year old engines) but historically youd expect a diesel to outlast 2 perol engines and the servicing costs to be lower on the diesel.   you didnt have ignition componants ,(spark plugs , leads distributor caps , consencers ) to routienly replace or adjust or fail on a wet night.



Good info here, but those simple bits have been replaced by much more complicated bits!
John


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## Deleted member 9849 (Jan 15, 2016)

Teutone said:


> I can tell you how. They only drive with 50mph on the motorway.
> 
> I tried it on a trip where we had plenty of time to get to our destination. You can save by driving slow. But boy it is SLOW! I can't do this. On average we do 60mph and I am happy to pay the difference for the more consumption. We are not too bad, ours is a low profile with no overcab bed. I still manage 30mpg ish.
> I found that weight isn't too much of a mpg killer, it's the aerodynamic. If you have a overcab bed your mpg will go up a lot for every 5mph you drive faster.



50mph on a motorway is too slow and I would suggest hazardous.The HGV's would be constantly pulling out into lane 2 to get past,then cars travelling in lane 2 pull into lane 3,then all the Audis,Beemers and Mercs that are in lane 3 have to brake sharply.


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## Teutone (Jan 15, 2016)

wakk44 said:


> 50mph on a motorway is too slow and I would suggest hazardous.The HGV's would be constantly pulling out into lane 2 to get past,then cars travelling in lane 2 pull into lane 3,then all the Audis,Beemers and Mercs that are in lane 3 have to brake sharply.



don't know when the last time was you drove on the motorway. I can see what you described on a daily basis. There are CARS driving slower than HGV's and as a result HGV's are constantly pulling out into the second lane just to be overtaking by another HGV in the thrid lane.

I feel for the time pressure the HGV's have these days but recently there seemed to be NO RULES for HGV's anymore. Just drive into a temp speed limit zone on the motorway. You will be surrounded by HGV's left righ and centre ignoring the 50mph limit sitting behind your bumper with a 10inch gap. Some even flash you to get out of the way.

And yes, 50mph is too slow on the motorway.:wave:


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## izwozral (Jan 15, 2016)

My first MH was a Talbot Express, petrol and LPG, on petrol I reckon it did 22-24mpg on a long straight run, on lpg my guess is 26-28mpg. it certainly ran smoother with better oomph on lpg and was bit of a cart horse on hills using petrol.
I sorta miss that old bird, whether it was because it was my first or I had grown to love it's little foibles, I don't know. 
There was a Talbot Express on Ebay a couple of years ago with verified 1200 odd miles on the clock, it was in A1 condition inside and out, if my memory serves me right, it sold for around the £12k mark.  I still get a twinge of regret not going for it.


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## Roger Haworth (Jan 15, 2016)

I presume everyone here is measuring m.p.g. by filling the tank, driving how ever many miles, then filling the tank again and dividing the miles driven by the gallons used between fills.

If on the other hand any of you are using the vehicle's computer to measure m.p.g. you are in my experience likely to get a very significantly different figure. For example on my van (Fiat Ducato 100 Mulitijet engine) if the computer says it's doing 36 m.p.g. the real figure, calculated as above, works out at about 30 m.p.g. My car is not quite so inaccurate - if the computer says 50 m.p.g. the real consumption figure is about 47 m.p.g. 

The other variable is the vehicle's milometer - how accurate is this? I suspect that most of these record more miles than you have really covered!?

 1 gallon = 4.54 litres.


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## Teutone (Jan 15, 2016)

Roger Haworth said:


> I presume everyone here is measuring m.p.g. by filling the tank, driving how ever many miles, then filling the tank again and dividing the miles driven by the gallons used between fills.
> 
> If on the other hand any of you are using the vehicle's computer to measure m.p.g. you are in my experience likely to get a very significantly different figure. For example on my van (Fiat Ducato 100 Mulitijet engine) if the computer says it's doing 36 m.p.g. the real figure, calculated as above, works out at about 30 m.p.g. My car is not quite so inaccurate - if the computer says 50 m.p.g. the real consumption figure is about 47 m.p.g.
> 
> ...



agree you can't rely on the dash. I measure tank for tank andmy speedo is quite close to the GPS. You have to use the speedo, there is nothing else?
But the safe method is always to fill up to really full (till you can see the level) and fill up again. Bit inconvenient but you don't need to do it all the time.
I have recorded miles and all diesel along the trip and as long as you fill up to full at the end even part filling can be taken into the calculation.
So my dash thingie isn't far out. 2-3mpg


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## Tezza33 (Jan 15, 2016)

On our last trip to France in August I measured from a full tank at the beginning to a full tank at the end, it worked out using the mileometer at 35mpg, but my speedo is wildly inaccurate, at 80kmh my satnav shows me doing 40mph instead of 50mph and that is confirmed when a roadside display tells you your speed, every trip I keep meaning to check the accuracy of the mileometer as well but I forget until I get home, 20% out is a lot though and brings my mpg figure down to 28mpg which I think would be about right, Hymer 584, 2.8jtd which is rarely out of 5th gear and my figures are always better in France, I don't see the point in worrying about it anyway, it is still cheap


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## Penny13 (Jan 15, 2016)

My Fiat Ducato low profile gets 25 to 26 per gallon, it's now in its third year from new ! I don't do technical it's what the computer tells me. I drive about 55 to 60 with lots of road variations.


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## jagmanx (Jan 15, 2016)

*27 Plus Honestly !*

Nearly 30 MPG sometimes
2.5 Litre Diesel on a  Renault master.
As others have said ..Keep below 55 MPH
Look ahead
I have recently fitted a
...
*Standard Tunit

3 Year Warranty
1 Year Engine and Drive Line Warranty
Typical fuel saving of 12%
R.R.P: £375.00*

This has made an improvement so now usually ALMOST  30 MP always

Obviously mountains etc have an impact but " A LIGHT RIGHT FOOT" is the key just ease off and your MPH will not drop !


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## invalid (Jan 15, 2016)

With my 3.5ton twin wheel transit 24ft long 2.5lt non turbo, fully loaded and foot almost wielded to the floor about 70mph, on a long journey I get between 22-28 mpg, I do sometimes coast. Not wishing to be stoned to death I produce BIO and with oil cost (old veg oil) at between 20-30ppl, and 15ppl to turn to bio, my labour is free =about 40ppl, sometimes a little cheaper if I pick up free oil. All I would say is just think how much you are saving by wild camping. The way I look at it is, I’m driving a very large heavy brick, but at least the wine is chilled.:cheers:


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## Firefox (Jan 15, 2016)

I get 33 mpg on all kinds of roads. 

I have measured this on two long trips full to full, 1800 miles round Scotland, motorway, country, and town driving, up and down steep hills.

I can get 36 mpg driving at 50-55mph in 6th gear on the motorway.

This is a 2.5 litre common rail diesel on a panel van. 

A friend who did the Scotland tour got slightly better on his panel van Citroen relay.


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## Steve121 (Jan 15, 2016)

wakk44 said:


> 50mph on a motorway is too slow and I would suggest hazardous.The HGV's would be constantly pulling out into lane 2 to get past,then cars travelling in lane 2 pull into lane 3,then all the Audis,Beemers and Mercs that are in lane 3 have to brake sharply.



By definition, motorways have at least two lanes, so other vehicles should always be able to overtake. It is ludicrous to suggest driving at 50mph is hazardous. If a vehicle changing lanes causes others to brake sharply, it is the lane-changing driver who is causing the hazard, NOT the vehicle driving at a lower speed (unless it's in the wrong lane of course, which can easily lead to prosecution now).


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## invalid (Jan 15, 2016)

If anyone wants to know the true meaning of fear, try driving a 1922 Rover tugging a vintage caravan between 20-30mph in the slow lane of a motorway.
For those interested in BIO I have put a link to my site for your information.
http://alifife.co.uk/wasteoilwestdevon/index.htm
:drive:


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## Fazerloz (Jan 15, 2016)

I checked my Ducato  with neck to neck fillings over several tanks of fuel when I got it and every time found the dash readout to be bang on .


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## pughed2 (Jan 15, 2016)

*cheapest mpg motorhome?*

I am going to upset you kiwi, and all the rest with high fuel consumption..........my 2003 fiat ducato 2.3jtd (turbo) diesel engine achieves up to 43mpg generalised driving around eu, in the trigano tribute lwb van conversion, with all the stops pulled out and carefully driven, but not necessarily at low speeds. I know this is frowned upon, but I only use the engine while accelerating, and uphill.........at all other times I find the 2.5ton loading allows it to coast for miles, but I do not take any chances. Anticipation is the driving word. Other users with exactly the same model get the same. Very reluctant to consider a change.............steve Bristol.


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## Beemer (Jan 15, 2016)

2.8JTD Ducato Fiat engine pulling up to 4.5t (more like 4t) gives me just over 20mpg average (UK), 25mpg best (France), I don't do slow.... have not got cruise control, but can sit with feet off the controls when in a traffic queue just ticking over and bimbling along.  I will, when it is legal and possible, drive at 3000 revs at an indicated 70mph, but 62mph according to sat nav.  If I wanted frugal mpg, I would have bought a van conversion.
Love the power I have pulling away and uphills.
Oh... I have a Tunit fitted, but don't know if there would be any difference without it on, as it was fitted when I purchased the vehicle, generally get 330 miles to a tankful.


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## Touringtheworld (Jan 15, 2016)

*Tailgating is the answer.*

My 2013 Sprinter 316 PVC averages about 26/27mpg fill to fill. 

The big revelation to me was when I followed my buddy in his 3 axle Autotrail for hours on end was 35/36mpg. 

........ Tailgating is the answer, all you have to do is trust the driver you are tailgating


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## mark61 (Jan 15, 2016)

Now mine is run in I get around 25 MPG. Sprinter 319 auto, all terrain tyres don't help much and I enjoy a bit of ooomph. I can get down to less then 19 if I really try.


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## Debs (Jan 15, 2016)

500 mpg


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## Debs (Jan 15, 2016)

:angel::wacko::banana::drive::lol-049::lol-049::lol-049:


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## Tezza33 (Jan 15, 2016)

Debs said:


> 500 mpg


I filled my tank to the brim when I returned from France in September, I have not had to fill up since and I have just checked it and amazingly it is still full, I have a tunit fitted but I think it is still full due to a combination of two national authorities, the wonderful NHS who throw all the s**t at me they could then topped it up by emptying grey water on me faster than Jim Hunter could only do in his dreams, then a good fuel saver by the DVLA with a fantastic fuel saving called 'SORN', looking to the future I might not need to fill up for a few Months View attachment 37182:mad1::mad1::mad1:


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## Deadsfo (Jan 15, 2016)

My old 1987 Merc 508 3.7ltr non turbo max speed 65 mph gives me 24 mpg under all conditions,I am hoping to do better when its run in ,it had 2572 kilometres on the clock when I got it,it now has 7850 klm .I expected  less MPG but I reckoned on offsetting  fuel costs against the hope that an old/brand new vehicle would have less breakdown costs and so far  (TOUCH WOOD) it has. In all probability, with a bit of luck and good servicing it could give me ,or someone else 200,00/300,00 miles, this could all come crashing down if the present witch hunt against Diesels is succesfull  but thats another story.
   Bio sounds good but I have a nagging worry about vegetable oils damaging rubber seals ,a new injector pump would negate any fuel savings.


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## Chris356 (Jan 15, 2016)

kiwi said:


> I have been reading various MPG claims in the forum and can't compete! I have a Talbot Harmony petrol and only achieve low 20's - even driving carefully. Similar models with diesel I hear achieve over 30MPG. And yes, my tyres are pumped up, not all my driving is uphill, and I don't have the pedal to the floor (although she doesn't exactly perform like a Formula one!)


At least you haven't got any electric modules , sensors or err valves to go faulty
I have a 2012 transit hobby 3.5 ton I get 25 mpg at 70mph but I only pay 80p litre have to buy 200 litres a time though


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## mark61 (Jan 16, 2016)

Chris356 said:


> At least you haven't got any electric modules , sensors or err valves to go faulty
> I have a 2012 transit hobby 3.5 ton I get 25 mpg at 70mph but I only pay 80p litre have to buy 200 litres a time though



I'm up for a few hundred litre thanks.


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## Mick H (Jan 16, 2016)

People have always tried to compare mpg, and always will, no doubt, but, IT IS UNLIKELY THAT ANY ARE ABLE TO CHECK WITH ACCURACY!

I say this because there are too many variables that enter into calculations. It has already been posted about the inaccuracies of speedo trip meters, but it doesn't end there.

You don't even know how much fuel you have put in, only how much you have paid for. Pumps are notoriously inaccurate, and in order to avoid problems with weight and measures, are normally set to deliver slightly more than they show. They are spot checked, on a regular basis, and it isn't unknown for the same pump to deliver a different quantity, when checked first thing in a morning, to later, the same day.

Because a fuel expands/contracts, according to temperature, again, you wouldn't know how this affected your calculations. 

Even filling tankful to tankful, can't be relied upon, because of the camber effect.

Wind speed is variable, and can have a dramatic effect on fuel consumption.

These are probably the main factors that affect calculations, but there are others.

To sum up, if you can't be sure how much fuel you have put in, or what mileage you have covered, how can you possibly check mpg, with any accuracy.


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## Wooie1958 (Jan 16, 2016)

Mine runs surprisingly well on red diesel    :drive:   and the cost is affordable    :dance:


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## RichardHelen262 (Jan 16, 2016)

Wooie1958 said:


> Mine runs surprisingly well on red diesel    :drive:   and the cost is affordable    :dance:



Most of the taxis in Huddersfield run very well on red too


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## trevskoda (Jan 16, 2016)

Teutone said:


> don't know when the last time was you drove on the motorway. I can see what you described on a daily basis. There are CARS driving slower than HGV's and as a result HGV's are constantly pulling out into the second lane just to be overtaking by another HGV in the thrid lane.
> 
> I feel for the time pressure the HGV's have these days but recently there seemed to be NO RULES for HGV's anymore. Just drive into a temp speed limit zone on the motorway. You will be surrounded by HGV's left righ and centre ignoring the 50mph limit sitting behind your bumper with a 10inch gap. Some even flash you to get out of the way.
> 
> And yes, 50mph is too slow on the motorway.:wave:



Nonsence,in n/ireland you are restricted to 45mph on r plates for first year of driving & that includes m/ways


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## trevskoda (Jan 16, 2016)

Wooie1958 said:


> Mine runs surprisingly well on red diesel    :drive:   and the cost is affordable    :dance:



25 ltr 28 sec heating oil and 2 ltrs of cooking oil, 28 pence for h/oil now and £1 litre c/oil but if caught you have to pay for tank being emptied and fine £1000 or van taken of you and crushed,not that i would do this.:angel:


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## invalid (Jan 16, 2016)

Before using RED, read= Excise Notice 75: fuel for road vehicles - Publications - GOV.UK  :scared:


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## kiwi (Jan 19, 2016)

pughed2 said:


> I am going to upset you kiwi, and all the rest with high fuel consumption..........
> 
> Many thanks to all who responded to this post - interesting comments and much appreciated - all except 'pughed2' who succeeded in "really upsetting (me)" with his 43mpg.:rolleyes2: I'm slowly climbing out of severe depression after that but now, when I'm in the slow lane struggling with 50mph and a fiat ducato passes me in the outside and doing 70mph, I can't even pretend he's getting a really low mpg!!
> Ah well, I still thoroughly enjoy the wonderful opportunities WildCamping POI's give me, mulling over poor performance and low mpg whilst tucked into some beautiful inconspicuous spot with no-one about, - just me, the van and an empty fuel tank - "happiness is..."


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## RichardHelen262 (Jan 20, 2016)

Can you really put a price on fun ?  Just fill it up and go off and enjoy yourself, and stop working out how many miles you are getting to the gallon.
Concentrate on how many smiles &#55357;&#56842;&#55357;&#56842;&#55357;&#56842; you get to the gallon


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## colinm (Jan 20, 2016)

On our 2.3L diesel Campscout (L4 H3 x2/50 PVC) we can reacon on getting around 30mpg on average, driving on motorway at 70mph(true, 74mph indicated) this will drop to around 25mpg, trundling around the lanes at low speed and  it will be doing around 35mpg.
 Previous van was a 1.9L petrol T25 VW PVC, we could usually expect high 20s in this. So your mpg would be fairly good for that van as far as I'm concerned.


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## Mick H (Jan 20, 2016)

Mick H said:


> People have always tried to compare mpg, and always will, no doubt, but, IT IS UNLIKELY THAT ANY ARE ABLE TO CHECK WITH ACCURACY!
> 
> I say this because there are too many variables that enter into calculations. It has already been posted about the inaccuracies of speedo trip meters, but it doesn't end there.
> 
> ...



Just curious, why hasn't anyone commented ref my above post on this issue?


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## 2cv (Jan 20, 2016)

Mick H said:


> Just curious, why hasn't anyone commented ref my above post on this issue?



It is possible to do it quite accurately.
Firstly it needs to be done over a period of time, so that on average wind will be neutral and overall filling inaccuracies become negligable,. Ideally at least a year to take account of seasonal variations and to give average usage.
Secondly to take account of guage inaccuracy a sat nav needs to be employed to compare actual and recorded mileages.
Using these methods should, I think, give a reasonably accurate result (for what it's worth)

Using the above methods I measured the mpg on a BX I once had over a period of years (sad I know!). It was interesting to note the lower mpg achieved in winter months each year, presumably due to extra choke needed.

On my 2.0 Trafic I achieve 33mpg.


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## Robmac (Jan 20, 2016)

Mick H said:


> Just curious, why hasn't anyone commented ref my above post on this issue?



Like most things in life, you can only work with the available parameters, which will give you a reasonable idea, if not 100% accurate.

To be honest, the only time I care about MPG is if it dips sharply for no apparent reason.


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## kris (Jan 20, 2016)

kiwi said:


> pughed2 said:
> 
> 
> > I am going to upset you kiwi, and all the rest with high fuel consumption..........
> ...


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## Mick H (Jan 20, 2016)

2cv said:


> It is possible to do it quite accurately.
> Firstly it needs to be done over a period of time, so that on average wind will be neutral and overall filling inaccuracies become negligable,. Ideally at least a year to take account of seasonal variations and to give average usage.
> Secondly to take account of guage inaccuracy a sat nav needs to be employed to compare actual and recorded mileages.
> Using these methods should, I think, give a reasonably accurate result (for what it's worth)
> ...



The old addage applies here, If you put rubbish in, then you get ................


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## Mick H (Jan 20, 2016)

Robmac said:


> Like most things in life, you can only work with the available parameters, which will give you a reasonable idea, if not 100% accurate.
> 
> To be honest, the only time I care about MPG is if it dips sharply for no apparent reason.



The point I tried to make was that you can't be at all certain if it IS a reasonable idea, let alone be anywhere near accurate!


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## Robmac (Jan 20, 2016)

Mick H said:


> The point I tried to make was that you can't be at all certain if it IS a reasonable idea, let alone be anywhere near accurate!



Surely consistency over several trips counts for something. I reckon I get just over 30 MPG, every time I have bothered to check, it is there or thereabouts.


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## ricc (Jan 20, 2016)

even if the mpg figures we each obtain arnt scientifically precise , they have value to us, taken over a period of years in all sorts of conditions and all the other variables they can give us a reasonable idea of what we as individualscan do to maximise the distance we get from each gallon of fuel,   it can even give indications of which vehicles are more economical.  precise ,accurate numbers that can be compared with somebody elses numbers arnt actually necessary

in short i dont give a stuff whether im actually  getting 34 or 36 to the gallon as long as its the highest mpg i can get , consistant with getting me and my load of baggage where i want to go in a reasonable time frame.


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## Fazerloz (Jan 20, 2016)

I keep an eye on my mpg as a indictor to the running of the van. Anything between 26- 31 I just put down to variables. if it were to suddenly drop to below 25 I would think something needs attention. Fiat 2.3 120 multijet  PVC.


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## Deleted member 919 (Jan 20, 2016)

heres mine 39 fills in just over a year.and 19.000 kilometers
Fuel Consumption details for 3000cc 2007 hymer b504cl on a Fiat Ducato Chassis owned by rebbyvid with average MPG of 36.80

Average number of days between refuelling stops: 13
Average Cost per litre: £1.163
Average Cost per Gallon: £5.28
Miles Per Litre: 8.08
Cost per Mile: £0.14


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## Deleted member 52918 (Jan 20, 2016)

invalid said:


> If anyone wants to know the true meaning of fear, try driving a 1922 Rover tugging a vintage caravan between 20-30mph in the slow lane of a motorway.
> For those interested in BIO I have put a link to my site for your information.
> http://alifife.co.uk/wasteoilwestdevon/index.htm
> :drive:[/QUOTE
> ...


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## Mick H (Jan 21, 2016)

Underground storage tanks ARE affected by temperature changes, even if these are not so great, also your vehicles tank IS definitely affected.

The camber effect IS NOT negated, to any significant degree, in the way that you have suggested.

Wind speed could average out, but certainly can't be taken for granted! It could be one of the reasons that calculations vary.

Accurate measurements? Have you read what I posted? How can you obtain accurate measurements. If it were possible, then I wouldn't have given my input!

When I worked for Marconi, we were fuel pump calibration specialists. That is where I have obtained most of my information, regarding this issue.

It is a waste of time, for the average driver, to attempt to check mpg. If you are only a small percentage out, this can be magnified, by checking over a period of time.

Most of us know that vehicle manufacturers figures are inaccurate, so why do we think that we can do better?


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## Deleted member 9849 (Jan 21, 2016)

Mick H said:


> ................................................................
> Most of us know that vehicle manufacturers figures are inaccurate, so why do we think that we can do better?



I always check my mpg at every fill using the brim to brim method in conjunction with the odometer.I realise that it will not be strictly accurate every time but over a period of several months it should give a fair indication of average fuel consumption.It has been as low as 22mpg right up to 31mpg.As long as it is consistently between these figures then I know the engine is working well and there is no cause for concern. 

I budget for 25mpg which I am happy with and have peace of mind knowing that the old lump is functioning well.


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## Robmac (Jan 21, 2016)

Mick H said:


> Underground storage tanks ARE affected by temperature changes, even if these are not so great, also your vehicles tank IS definitely affected.
> 
> The camber effect IS NOT negated, to any significant degree, in the way that you have suggested.
> 
> ...



Whilst I appreciate your obvious knowledge of the subject in hand, are you suggesting that we should be completely oblivious to how our vehicles are performing, or do you have a better solution?

That may sound condescending, but it isn't supposed to, it is a genuine question.


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## Mick H (Jan 21, 2016)

Robmac said:


> Whilst I appreciate your obvious knowledge of the subject in hand, are you suggesting that we should be completely oblivious to how our vehicles are performing, or do you have a better solution?
> 
> That may sound condescending, but it isn't supposed to, it is a genuine question.




I was only attempting to raise awareness, that because there are far too many variables, fuel consumption figures are ONLY ESTIMATES, and should NOT be regarded as accurate. 

As with most things, people will believe what they want to.  Topics like this will be raised in future posts, but possibly, I have given 'Thinking people' food for thought.


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## Fazerloz (Jan 21, 2016)

Mick H said:


> Because a fuel expands/contracts, according to temperature, again, you wouldn't know how this affected your calculations. .



Is this not negated on modern vehicles by the fuel temperature sensor. And the automatic temperature compensator on modern fuel dispensers. If not we had all better fill up first thing in the morning when the fuel is more dense.


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## ricc (Jan 21, 2016)

Fazerloz said:


> Is this not negated on modern vehicles by the fuel temperature sensor. And the automatic temperature compensator on modern fuel dispensers. If not we had all better fill up first thing in the morning when the fuel is more dense.





bin doing exactly that for years


incidentally i fail to see how thermal expansion/contraction of the fuel in the vehicle tank would have any effect on the metering in the forecourt pump of the fuel supplied from an underground tank.

furthermore the camber effect on the fuel in the vehicle is , as wints posted , only effecting the level of the fuel in the  2 inch diameter filler pipe , most forecourts are pretty level, reallistically  a couple of ccs in a 50 plus litre fill up , not something id get my knickers in a twist over,  though others may be more anal.


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## Obanboy666 (Jan 21, 2016)

Just parked up in Penrith after returning from Skye and beyond. 2013 Luton cab c class, 2.3 Lt Fiat euro 5 engine.
1150 miles up hill and down dale, pedal to the metal returning to Penrith tonight 70 on the M6.
24.6 mpg going of dash display, will fill up again in the morning to compare but last time I checked they were identical.
Motorhome was near the 3.5 limit as I carried extra water and my Genny.  I reckon a low line c class will be better but I knew when I started motorhoming that they were heavy on fuel.
It is still better than when I pulled the caravan with a 2011 Hyundai Santa Fe, never better than 24 mpg.


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## hextal (Jan 21, 2016)

Mick H said:


> Underground storage tanks ARE affected by temperature changes, even if these are not so great, also your vehicles tank IS definitely affected.
> 
> The camber effect IS NOT negated, to any significant degree, in the way that you have suggested.
> 
> ...





Surely the purpose of 'the average driver' working out their mpg is for relative purposes rather than as an absolute, so a general range as opposed to a highly precise figure is what is being looked for.

Whilst testing in fully controlled lab conditions will invariably yield more consistently accurate data, there is much that must be tested in real world conditions, which are by nature, less controlled.  Just because there are uncontrolled factors does not automatically render this data worthless, particularly when it is averaged over large sets of journeys, drivers, locations, temperatures.

I believe this to be a good example of the difference between a scientific approach to a subject and an engineering approach to a subject.

Both have their merits and their shortcomings.


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## Fazerloz (Jan 22, 2016)

If anyone is interested about expansion of fuel. As a rule of thumb, the volume of a litre of petrol changes by approximately 1.2ml per 1°C, and diesel changes by approx. 0.8 ml per 1°C., the energy value per litre remains the same.  I will let you do the maths to see how much more your fuel grows on a tank full of fuel. This is why its not wise to fill and then park up especially in the summer.
As an aside I am personally more bothered over the increase in the addition of Ethanol into fuels, a real devil sat in your tank especially in older vehicles, and by that pretty much most things made before they started adding Ethanol a few years ago.


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## 2cv (Jan 22, 2016)

Ethanol in fuel is a real problem in older vehicles. Not only does it have a harmful effect on components, but it can cause weak running even in relatively recent vehicles with ECUs.
Apparently it can also affect fuel consumption. Another fantastic EU cock up, they've even tried 85% ethanol in a few places in France. At least here in Britain it's only 5 and 10% for now.


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## Fazerloz (Jan 22, 2016)

2cv said:


> Ethanol in fuel is a real problem in older vehicles. Not only does it have a harmful effect on components, but it can cause weak running even in relatively recent vehicles with ECUs.
> Apparently it can also affect fuel consumption. Another fantastic EU cock up, they've even tried 85% ethanol in a few places in France. At least here in Britain it's only 5 and 10% for now.



1.4 litres of Ethanol contains the same amount of energy as 1 litre of petrol.


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## RoadTrek Boy (Jan 22, 2016)

Just to make you lot feel better, at the moment I am averaging 9 - 11MPG, this is all fairly short runs and being in Torbay it's hills everywhere. 3950Kg 5.2L v8. Petrol.  :wacko::drive:


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## Fazerloz (Jan 22, 2016)

But it will sound sweet. Is that on the readout, if so don't forget to add your 20% for little American gallons. Just to make you feel better. :wave:


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## RoadTrek Boy (Jan 22, 2016)

I have a Scanguage fitted to give me a good idea, but the odometer is in Km and I work it out on fill ups.   But on a run coming down from London I managed 15MPG.


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## RoadTrek Boy (Jan 22, 2016)

swiftcamper said:


> Just a baby then , ours is 8.1 ,L v8 about a mile and a half to a litre of lpg.



That's roughly 6 to 7MPG, I take it that's on a run.


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