If you trust your trip computer, try this simple test. Immediately before filling up, add the distance travelled since the last fill-up to the number of miles remaining in the tank as indicated by the computer. This will give the range of the tank. Immediately after filling up read the miles remaining in the tank (i.e. the range of the tank) on the computer and compare this with the "before fill-up" range. On my car the "before fill-up" figure is consistently about 60 miles greater than the "after fill-up" figure.
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How odd but I do wonder about the accuracy of these devices. I haven't checked "miles remaining" but mpg recorded for my new Hyundai 130 i.6 petrol for the first 1238 miles is 44.3, which seems good. By my own calculation, it is 36.51, which is not. I wonder which is right?
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Old Fabia was virtually spot on - new one reads about 5/6% optimisticly!
I doubt it is the case that tyre/wheel size might make a difference, but the old one was shod with 185/65/14s and new one with 195/50/15s - now where's that link where you can compare diameters of tyres...
Help!
Edited by b308 on 03/04/2008 at 14:15
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Never quite sure about how you do a manual reading - people talk of "brim to brim". Does that mean keep putting in fuel until you can see the whites of its eyes or until the pump automatically clicks off the first time?
If its the latter, how do you know all pumps will click at the same point? I ask because I don't know the mechanism that makes it click off anyway!
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Never known the Scenic's to be more than 1 mpg out. Which is depressing when it shows 38 mpg.
Cheers
DP
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I calculate mine on a brim-to-brim method, and shows the on-board computer to be about 5% optimistic.
I suppose there are different points on different pumps where it clicks off, but I can't imagine it would alter the figure more than about 0.1 of an mpg. bearing in mind that the pump will click off when fuel is in the filler neck, so only a fraction of a litre increases the fuel level to that point.
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The Picasso 1.6 Hdi is generally 7-9% optimistic on the trip computer. I have long term figures from brim to brim to back this up with long term and medium term averages. I will post this next time I am in the UK.
The miles remaining is VERY dependent on the the throttle setting at the time. It does not base the 'Miles to go' to the long term recorded consumption, merely the last few minutes!
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"It does not base the 'Miles to go' to the long term recorded consumption, merely the last few minutes!"
I think the Mazda6 does this - makes sense because if the longterm figure based on motorway cruising and you're stuck in town now you'd not want it being optimistic. But when it reads 8 miles left and you can fit in over 10 litres something is wrong ;-)
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The miles remaining is VERY dependent on the the throttle setting at the time. It does not base the 'Miles to go' to the long term recorded consumption merely the last few minutes!
I seem to recall reading in the user manual that the range is calculated based on the last 20 -30 miles fuel consumption on my lovely green vectra with trip computer. My various bangernomics big VXs have always been within about 1 mpg on the computer compared with long term brim to brim.
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Once I run my Mazda6 until it read miles remaining 8! But the fuel warning light had not come on and the needle was not in the red - but new car and I didn't know which to believe.
Filled it up to the brim and it had at least 10 litres left in it. So assuming say 38mpg I would have gotten over 80 more miles. Probably more than that even.
So when it now says range maybe 560-600 miles is that about 100 miles optimitistic?
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I find the trip computer on the old shape Passats and now on my A4 very accurate, at most .5 mpg optimistic over manual brim-brim calculations.
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