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Value of Fuel Consumption Indicators
During my research for this blog, I have read a great deal of contradictory information about the average real fuel consumption of several popular vehicles. We all know that the style of driving or the outdoor temperature has an effect on fuel consumption, so it is normal that different measurements of consumption vary from one driver to another or one region to another.However, to get precise consumption measurements, it is rare for consumers to go even as far as the driver’s seat. They simply take note of what the dashboard indicator displays. These indicators are very practical, but how precise are they? Good question.
First of all, you should know that the calculation of fuel consumption is based on the quantity of fuel injected in the engine and this quantity is extrapolated in terms of injector opening time and the flow that it can attain. Distance is measured by the odometer and this info comes most often from the rotation sensors on the wheels of the anti-lock braking system. These two measurements are in theory very precise.
Surprise! It seems that certain displays are a little too optimistic, a reality that I have observed on numerous occasions in my test drives. I regularly see significant differences in the order of 20% among certain manufacturers. And I am not alone: see this article from my British counterparts at the magazine Fifth Gear. In one case, the difference is 8%, while in another optimism exceeds 40%!
How can this be? This may be surprising to you, but I do not have the explanation for this particular case! But to get absolutely precise measurements, I know only one method: fill it up to the top, drive, fill it up again and calculate the average fuel consumption from the odometer values and the gas pump. This will be precise to the extent that the diameter of the tires is identical to that of the originals and correctly inflated as well.
To return to the differences observed, I know that the speedometers are almost all calibrated to indicate slightly more than reality, while odometers are all absolutely rigorous. In both cases, legal considerations dictate the precision: there can be no possible legal challenge for speed (in the case of highway driving infractions) and, in the case of distance, nobody can claim a warranty has ended too early, for example.
Note that there are also independent indicators like this one, but I would be interested in knowing know how precise it is, since these displays take their data from the same point (the engine computer) as the indicator mounted in standard model equipment.
So is it possible to be accurate? Why are fuel consumption indicators so unreliable? I am still waiting for an interesting explanation. Do you have one?
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