MPG claims + petrol v. diesel

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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.
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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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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.
 
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.

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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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.
 
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.
 
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.
 
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.
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1.4 litres of Ethanol contains the same amount of energy as 1 litre of petrol.
 
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::eek::drive:
 
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:
 
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. :cry: But on a run coming down from London I managed 15MPG. :)
 
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