OBC fuel economy accuracy?

[Russell]

Wonder how accurate does the e34 obc measure fuel economy. I tried a comparison with mine years ago and it it seemd to be close what you would find with a tank to tank comparison. Looks like some newer cars are lying to the owners. Perhaps all do, expecially since E10 fuel is almost everywhere.

Your Fuel Economy Gauge Is Fibbing — Edmunds.com

[genphreak]

I trust mine implicitly, but unlike that article, I accept +/-5% as more than reasonable.

I doubt the accuracy of people calculating at the pump over 2000km- you have to sample 10,000km or more to be accurate particularly if you fill at different pumps as each stops filling the tank at a different level.

BMW's econometers measure all the right things, they are not a half-arsed gauge. I wuld have thought most modern ones are good too. I do know that in any BMW, if your odometer is accurate, so is your econometer. I don't know about new car economy being accurtely reported, though modern 6, 7 speed and CV transmissions really do help city cycle economy. Older cars with autos start to use more fuel because the trans stops changing at quite the right times or you encounter slip where you shouldn't. Many engines are more efficient nowadays, but the Volumetric Efficiency of a combustion engine is still appallingly low, given how much the human race (ab)uses it on our poor little planet. A good and interesting article, but the amount of inaccuracy they found seems a bit churlish.