They don't deliberately tell lies. It's just that by the way they work they're not very accurate. As the advance of technology comes up with more and more better methods of performing the calculations the accuracy will increase.
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L\'escargot.
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If that's the case why don't we hear from people saying that their fuel computer under-reads by 10-15%?
They always eem to be optomistic rather than pessimistic. Me, marketing ploy, cynical, never???
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If that's the case why don't we hear from people saying that their fuel computer under-reads by 10-15%?
What does it matter? The onboard "computer" fuel consumption reading will never affect my opinion of my car or of the manufacturer. I take the view that the "computers" are toys for my amusement only and accept the readings on that basis.
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L\'escargot.
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I agree to a point and I stated that I think the actual economy being delivered is good for a car of it's size. My point is that if something is fitted to a car, I believe that you should expect reasonable performance from it.
I know I'm taking it to extremes here but what if your speedo had huge inaccuracies?
My previous 3 cars all had fairly accurate fuel computers so obviously it can be done fairly easily.
Maybe I'm being a bit cynical but if I beleived the FC and told my friends that my S-max was delivering 51 MPG that would be great PR for Ford wouldn't it?
I know it's a small thing but the small things do count and some things are more important to some people that others.
Thanks anyway.
a900ss
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Well, VW''s figure for my 1.6 FSI Golf MKV state sa combined fuel consumption figure of 41.7 mpg and since I have had my car, during the last 28 months or so, I've got 41.5 mpg or thereabouts and this figure agrees, usually very closely, with that read out from the onboard computer.
I think that the worse deviation from my brim/brim calculations and the computer's readout have been of the order of 2% which I don't think is bad.
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If that's the case why don't we hear from people saying that their fuel computer under-reads by 10-15%?
Funny you should say that - the one in Mrs B's Panda Multijet is about 10% pessimistic - took it for a run to Cardiff and back via Oxford a few weeks ago and couldn't get the MPG readout above 51 mpg. Actual brim-to-brim was a nudge under 57 mpg, which although some way short of what the manufacturer and the motoring press claim it will do is still pretty damn good IMO. Didn't feel like I'd been running underneath it, either.
FWIW I never believe any trip computer - I just use the figure as a general guide and it's amazing what an incentive it is to behave when you're trying to make the numbers go as high as possible...
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A900SS's point is a fair one in one sense, though. I'll be taking a two-day test drive in a C4 (Grand) Picasso soon, and no doubt I'll be wondering how close it's getting to it's 45mpg Combined value, and that guide will come from the computer. When I do the same in an S-Max or anything else, I'll look at the computer there too, and if one is markedly lower than the other, it might - just might - influence my buying decision. Since manufacturers aren't constrained by construction and use regs (as they are with speedometers and odometers) they can be as cynical as they like on how high the computer reads. (I suppose a customer with an inaccurate computer might have some come-back under the Sale of Goods Act - fit for purpose and all that - but it's hardly grounds for rejecting the entire car.)
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If you have confidence in the accuracy of your fuel computer just carry out this simple test.
Immediately before you fill up note the number of miles (from your odometer) since the last fill and the number of miles the computer says you have left in your tank, and add the two together. This will give you the the (theoretical) capacity of your tank in miles. Immediately after you have filled up note how many miles the computer says you have left in your tank and compare this with the aforementioned calculated figure. Do this every time you fill up. Let us know the results.
Mine consistently comes to about 500 before filling up compared to about 440 afterwards!
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L\'escargot.
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I don't know how it works on our C5 but it is always optimistic. As the fuel gauge seems pretty accurate, isn't the easiest way to compute mpg simply to marry the odometer reading to the amount of fuel in the tank, or is this too simplistic?
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>sn't the easiest way to compute mpg simply to marry the odometer reading to the amount of fuel in the tank, or is this too simplistic?
Accurate? No. Adequate? I think so. I don't have a fuel computer, and I reckon 300 miles from full to half-full is about par. The orange feed-me light comes on reliably with about 10 litres left. When I fill up, I can usually guess to within two litres how much it'll take. Of course, if I'd paid £300 extra for the computer when I ordered the car...
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I don't know how it works on our C5 but it is always optimistic. As the fuel gauge seems pretty accurate isn't the easiest way to compute mpg simply to marry the odometer reading to the amount of fuel in the tank or is this too simplistic?
No. It seems like most fuel gauges go:
Full
Full
Full
A bit under full
Half way
Empty
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