Average Mpg Readout

[Paul99]

Hi,

Jan 07 (facelift) TX3 5 door 2.0 litre diesel. Average mpg displayed on readout = 44.8mpg. Actual mpg calculated over 475 miles using 42.68 litres (9.39 gallons) calculates to 50.67 mpg. I'm pleased with this, but why the discrepency between the readout and the calculation? Is there any way to make the readout more accurate?

Thanks

[Jamesbelfast]

The onboard milegae calculator only extrapulates its readings based on engine and distance data. The distance calculation will not be 100% (odometers alone can be as much as 10% inaccurate. And as the system doesn't have a flow meter then there can be as much as a 25% discreptancy at times. It only takes the slightest inaccuracy in any of the data for the figures to influence the readings.

Even your own calculations may be subject to error.

I would say such systems are liars but they can be economical with the truth.:)

[Pat2u]

I have owned a good few toyota vehicle cruisers/ravs/avensis and more never ever had a true dash readout yet, so i ignore the dash.

I use my iPhone app which is more or less bang on from each fill up.

[Roker]

Before I retire my expertise was in calibration. (Not Cars) There are so many uncertainties in Toyota's calculation and yours, which affects the accuracy of the reading, neither reading will be exact. All the uncertainties total up to give an inaccuracy

Toyota is probably using the firing period of the injection to measure quantity vs distance, the injectors and tyre wear will effect this.

Your measurement for quantity will be inaccurate + again how are you measuring distance?

Temperature will also be a factor in both calculations.

Even the petrol pumps are not exact, there is aways an error or uncetainty right back to the standards laboratory the has the most accurate standard.

[Jamesbelfast]

Even GPS systems can't be gauranteed to be accurate. Most network systems available to the public only work in two dimensions so if you drive over a load of hills and dales................

Like all statistics you need a good number of readings to come to a reasonably acccurate conclusion.