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Well isn't this nice....

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Old Aug 12th, 2019, 06:54   #1
Mkengineering
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Default Well isn't this nice....

Driving this morning and my MPG was reading this lovely number



Granted I was doing 52mph but either way still was nice too see hahha
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Old Aug 12th, 2019, 07:35   #2
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Even if slightly optimistic[and I'm not saying it is] that's pretty good going.Having said that just after I bought my V70 I got just over 40 mpg on a 250ml round trip at predominantly 60mph.
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Old Aug 12th, 2019, 10:07   #3
john.wigley
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You are both doing very well. I have never even approached 40 MPG in my V70. The OBC currently shows 30.3, and my spreadsheet figure over 10K+ miles is only 29.5. I didn't think that was too bad for a 2.4 litre, but it pales into insignificance when compared with your figures. I'm not a particularly hard driver, but don't do that many long runs these days. The car appears to run well and I don't appear to be leaking fuel, but clearly it is returning significantly less than comparable cars seem to manage.

I do relatively few miles these days (3 - 4K pa in the V70), so the cost of fuel is not the major factor in my motoring expenses, but it would still be a useful saving if I could reduce my consumption by maybe 10 - 20% to bring it into the mid 30s at least. On the plus side, the near zero depreciation more than compensates for spending a little more at the pumps.

As an aside, I've also owned 7 series cars which have returned significantly differing MPG figures over extended periods of comparable give and take driving. One car (carb) never did much more than 23, while another (FI) achieved 28 over 60k+ miles. Perhaps it depends on the individual car as much as the driver?

Regards, John.
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Old Aug 12th, 2019, 12:29   #4
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Yikes!
I have to admit I don't keep too close a check on my mpg (probably because I don't want to know the truth) but for the driving I do, mostly 10 miles each way to work and around Milton Keynes with all of its dual carriageways and roundabouts, I reckon on 20mpg. Keep remembering that the depreciation on a 20 year old V70 is negligible to non existent.
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Old Aug 12th, 2019, 20:07   #5
Dippydog
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When I achieved that mpg it was because I was sat at 60mph most of the journey due to following a step daughter whose Focus diesel estate would flicker its oil light at speeds above that.So granted it was something of a one off,most of my driving is around town where low 20's are more the norm.I don't obsess about fuel consumption[otherwise I wouldn't run a 2.4 V70,3.0 Omega and a 960] although I like to know what's achievable,but I keep an eye on the average shown as a possible indicator of problems.
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Old Aug 13th, 2019, 15:19   #6
Mkengineering
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Well I was just seeing what the black panther could achieve. But my normal mpg is around 25 to 27mpg on a long run
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Old Aug 14th, 2019, 16:11   #7
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These MPG figures on the dash tend to be horrendously optimistic, but worse on the TDI's than the petrols.

I get 37MPG on a filler-neck brim figure from my 10v petrol, and that tallies with a dash figure of 39.5MPG

The TDI was born to lie (there is a factor-modifier figure in the MSA15 control software!) so a dashboard figure of 63.2MPG on a long run is only achieving 55MPG, but that is fairly consistent for the roads around here.
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Old Aug 15th, 2019, 09:33   #8
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Hi all

I have started using fuelly.com, which is free, to track fuel consumption.

It works most easily if you fill up each time you refuel.

I have always wondered how (which sensors) the car can use to know how much fuel (gallons etc) have been consumed, and I therefore don't see how the onboard fuel calcs can be 100% accurate.

I don't think fuel gauge or injector timing provide enough info, and there is no fuel meter as far as I know.

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Old Aug 15th, 2019, 10:59   #9
john.wigley
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You make a very valid point, Steve. While I do not obsess over specific fuel consumption, I do record every drop of fuel that I put in my V70 against the mileage covered. (I imagine that 'fuelly.com' works on a similar principle.)

Since purchase, over almost 11k miles, the car has averaged 29.5 MPG calculated thus. The OBC, which indicates a running average of 30.3. therefore over reads by 0.8 MPG or 2.7%.

Like you, I do not fully understand how the car computes this figure, but assume that there must be a flow-meter in the system which compares the amount of fuel used with the distance travelled.

Out of interest, my car is of a similar specification to your '98 10V Auto, and has covered just under 130k miles.

Regards, John.
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Old Aug 15th, 2019, 20:31   #10
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The fuel flow is calculated from the (injector flow-rate x engine speed x strokes per rev)

For an electronic diesel engine, this is trivial. Injected fuel mass has been used as a basis figure since the early 1990's, all of the early combustion parameter mapping was done with the flow in (mg/stroke) as the "fuel axis" for all the 2D and 3D maps.

For a 5cyl Volvo engine, there are 2.5 strokes/rev.

So the fuel flow at 2000rpm on an engine injecting at 15mg/stroke is;

15 x 2000 x 2.5 = 75,000 mg/min

Divide that through by 1E6 to convert from mg to kg, and then multiply by 60 to go from minutes to hours, and you get;

75,000 x 60 / 1000000 = 4.5 kg/hr of fuel flow

The density of EN590 diesel is around 0.86 kg/litre, so if you divide that figure above by the density factor, you arrive at something like 5.25litres/hr.

The engine controller has this calculation done from second to second, and can pass this to the instrument pack in that form. All the instrument cluster has to do is to divide that figure by the vehicle speed in kph and then multiply the result by 100, and you arrive at a figure on the display of litres / 100km, which is the standardised way of representing fuel consumption in Europe. The iPack has a built-in conversion factor to go from litres/100km to mpg in one easy step, so depending on the display settings of the pack, the driver can see either format.
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