Don't believe everything computers tell you!

[Orcade-Ian]

Perhaps it's not just VW who are pulling the wool?


Christine and I have just returned from a great trip from Orkney to the Netherlands, Germany and Austria - not with the Daimler or the GoldWing, but with our Peugeot Partner Tepee.  I decided before this trip that I would do a bit of testing of various parameters which come up on the display and in particular the overall MPG figure.
We have been using a Garmin 60 csx GPS unit successfully for a few years now, so I thought I would use this to accurately log the distance travelled.  We fuelled up to the brim before we left and disregarded that fuel quantity. We kept all of the till receipts and filled up finally when we returned home and included that in the total.
On such a long trip with many visits to the fuel stations, any small discrepancy in total volume would be insignificant.
We travelled a total of 2960 miles according to the 12 channel GPS and we used 55 gallons of fuel, or 230 litres

This works out at 52.44 mpg, yet the digital display on the dash of the Peugeot read 55.3mpg.  That might not sound much of a discrepancy, but it's close to a 6% error. 

Is this just down to the difficulty in accurately measuring fuel flow and therefore specific fuel consumption, or are the dark forces at work here as well as at VW?

You (and they) can come up with all kinds of reasons, such as odometer error, tyre wear (incidentally ours were almost new before the trip) but the error is always in the same direction. Food for thought!
Ian

[Rozabikes Tim]

I have always find that sort of error on most my cars and vans when comparing computer to reality.

[Johnwebley]

advertised fuel figures are my pet hate,


 they are NOT done on a road run,but in a lab,and the vehicle ,all ancillaries are turned off,

 the figures achieved this way are a down right fraud,

in recent real world test,several vehicles failed to get within 30%

http://www.which.co.uk/cars/choosing-a-car/how-we-test-cars/how-we-test-mpg/

http://www.telegraph.co.uk/motoring/green-motoring/9241054/Fuel-economy-why-your-car-wont-match-the-official-mpg.html

[mike the bike]

I expect you had the radio on, headlamps, indicators occasionally and, of course, brake lights.  there were probably hills to contend with and the occasional traffic; limping along in first for a while, not to mention a boot full of your buckets and spades. These are realistic driving conditions so your figure isn't too far from their test track figures.

[Orcade-Ian]

Perhaps I didn't make it clear, this has nothing to do with ADVERTISED figures, what I'm illustrating is that the ACTUAL fuel consumption differs from the display figure on the dash.  Radio, indicators hills etc were a common factor in both figures.
Ian

[steff750]

why am i reading this?
computers dont make mistakes
not until you add the humans ,or more to the point real world conditions
this is just down to not being able to accurately measuring fuel consumption, driving conditions plus your heavy trotters,i bet the computer didnt tell you how many hills you went up or how many times you had to stop and start
i would check for fuel leaks to be on the safe side 

[mike the bike]

I see your point.  I would say that the computer is just making an educated guess.

[Bryanj]

Considering that construction and use regs say that the speedo has to be within 10% accurate that error is well within parameters. Normally they read on the high side, which would then show more miles so a better MPG

[Orcade-Ian]

Many thanks folk for the variety of interesting replies.  It would appear that most you have misunderstood or misread the original entry.  As both sets of figures, namely GPS distance plus fuel receipts as one set and distance recorded by the vehicle and average consumption shown on the computer as the other set, were recorded on the same 3000 mile trip, then no matter what load we were carrying (buckets and spades eh?) and no matter how heavy my right foot was and no matter how many hills or stop starts we encountered (or even if there was a fuel leak - now, really?) then those factors have no consequence in this COMPARISON of data sets, as they would apply EQUALLY to both sets.
I am well aware of the speedo error allowance but had hoped to open a sensible debate about misleading info from vehicles.  I also realise that test data given by vehicle manufacturers is obtained in ideal lab type conditions however that was not really in the discussion.
If we don't question the validity of data now and then, we run the risk of continuing to be deliberately misled.

[steff750]

You are starting to bore me know
this forum is about sohc motorcycles
not cars or computers
take your moans elsewhere
you are doing my head in

[Nurse Julie]

You are starting to bore me know
this forum is about sohc motorcycles
not cars or computers
take your moans elsewhere
you are doing my head in

That's a bit of a harsh reply. It was posted in the misc / open area which was totally appropriate and interesting reading to some of us. If you don't like what your seeing, don't bother reading it and certainly don't reply with comments like that. Go and take your strop out on someone else. Also, it would be considered courteous to actually donate to the running of this forum before you go sounding off but, have you donated .............NO

[JamesH]

Orcadian - how do you know you re-filled the tank to EXACTLY the same level before / after? Did you fill the tank until the filler spout was literally overflowing on both occasions?. I'm interested. Steff - what's up? Got out of bed the wrong side today or is it pissing down in Wales like it is here in Brighton?

[paul G]

 ;

You are starting to bore me know
this forum is about sohc motorcycles
not cars or computers
take your moans elsewhere
you are doing my head in

That's a bit of a harsh reply. It was posted in the misc / open area which was totally appropriate and interesting reading to some of us. If you don't like what your seeing, don't bother reading it and certainly don't reply with comments like that. Go and take your strop out on someone else. Also, it would be considered courteous to actually donate to the running of this forum before you go sounding off but, have you donated .............NO

 

[JamesH]

Sorry Orcadian, just re-read my question and I'm not being sarcastic, I'm actually genuinely interested.

I used to calibrate these vehicles in a former life so have a little knowledge here....

J

[MCTID]

Oooh some stroppy comments flying around on this post.....however I'll wade in as well as Ordcadian does make some valid points about a subject which affects us all.

My Sister In Law (an experienced Motorist) bought a very nice Chevrolet Cruze a few years ago. It looked very fetching in dark metallic blue with a smart interior and lots of toys. She thought she had got a really good deal including a generous part ex.

As it was a 1.6 litre Petrol engine, she expected 'reasonable' fuel consumption from a low mileage 3 year old car, and although she had researched the 'Official' fuel consumption figures for the Cruze, she was horrified at its real world return of around 16 - 18MPG.

Despite various discussions with the Dealer she cut her losses after a couple of months and moved on.